WBBSE Solutions For Class 10 Physical Science And Environment Physical And Chemical Properties Of Elements Electric Current And Chemical Reactions

Electric Current And Chemical Reactions Topic A Electrolyte And Electrolysis Synopsis

WBBSE Class 10 Physical and Chemical Properties Overview

1. Compounds, in their molten state or in solution undergo chemical decomposition to yield their respective ions and are called electrolytic substances or electrolytes. Acids such as HCI, H₂SO₄ etc., bases such as KOH, NaOH etc., and an aqueous solution of salts such as NaCI, KCI etc., are some examples of electrolytes.

On the other hand, compounds which do not conduct electricity in their molten state or in solution are called non-electrolytes. Sugar, wax, glucose, butter etc., are some examples of non-electrolytes.

2. Electrolytes which dissociate almost completely into their constituent ions in molten state or in solution and thus have high electrical conductivity are called strong electrolytes.

For example, HCI, NaOH, NaCI etc. are strong electrolytes. On the other hand, electrolytes that dissociate partially into their constituent ions in molten state or in solution and thus have low electrical conductivity are known as weak electrolytes. For example, CH₃COOH, NH₄OH etc., are weak electrolytes.

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3. Electrolytes dissociate spontaneously in solution to form cations and anions which are responsible for conduction of electricity. Undissociated molecules are non-conductors of electricity. In fact, electrons do not play any role in conduction of electricity through an electrolyte.

4. The number of cations and anions produced due to the dissociation of an electrolyte in a solution may not be equal but the total positive charge of the cations at any moment during the conduction of electricity must be equal to the total negative charge of the anions.

5. The fraction of total number of molecules of an electrolyte that ionise in molten or dissolved state under a particular condition is called the degree of dissociation of that electrolyte.

Obviously, the degree of dissociation of a strong electrolyte at any point is more (almost equal to one) than that that of a weak electrolyte (less than one). With the increase in the degree of dissociation, the conductance of the corresponding electrolyte also increases.

Understanding Electric Current in Chemistry

6. In solid metallic conductors, free electrons conduct electricity, but in case of electrolytic solutions, the ions produced due to dissociation of the electrolyte conduct electricity.

The metal atoms do not change their position while conducting electricity but the ions in the electrolytic solution change their positions while conducting electricity. Besides, the conductivity of a metallic conductor is almost 106 times than that of an electrolytic solution.

7. The process by which an electrolyte in its molten state or in solution undergoes chemical decomposition to form new substances due to passage of electricity is known as electrolysis.

8. The apparatus in which electrolysis is carried out is known as voltameter. The setup consists of a vessel (generally made of glass or fibre) in which the electrolytic solution (either molten or dissolved in a suitable solvent) is taken along with the corresponding
electrodes.

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Wbbse Class 10 Current Electricity Questions And Answers

9. The two metallic rods or plates that are partially immersed in the electrolytic solution are known as electrodes. Generally the metals which are good conductors of electricity such as platinum, copper, iron etc., are taken as electrodes.

10. Graphite, although being a non-metal is also used as an electrode because of its ability to conduct electricity. The electrode which is connected to the negative terminal of a battery is called the cathode while the other electrode which is connected to the positive terminal of the battery is known as the anode.

11. Electrolysis takes place when direct current (DC) is passed through an electrolyte in its molten or dissolved state with the help of the electrodes. The cations move towards the cathode and are converted into neutral atoms or radicals by accepting electrons i.e.,
reduction occurs at the cathode.

12. On the other hand, the anions move towards the anode and are converted into neutral atoms or radicals by releasing electrons i.e., oxidation occurs at the anode.

13. Pure water is a non-conductor of electricity. However, in the presence of a trace amount of acid or base, water can conduct electricity. Electrolysis of water produces hydrogen at the cathode and oxygen at the anode.

14. When an aqueous solution of CuSO₄ is electrolysed using copper electrodes, copper atoms from the anode are oxidised to Cu²⁺ ions which passes into the solution whereas Cu²⁺ ions from the solution are reduced to Cu atoms by accepting electrons and get deposited at the cathode. Consequently, the anode gradually dissolves into the solution while the cathode becomes thicker.

Electric Current And Chemical Reactions Topic A Electrolyte And Electrolysis Short And Long Answer Type Questions:

Question 1. What are electrolytes and nonelectrolytes? Give example.

Answer:

Electrolytes: An electrolyte is a compound which conducts electricity in molten state or in aqueous solution and thus dissociates to form ions in solution.

Example:
Acid: HCI, HNO₃, H₂SO₄, CH₃COOH etc.
Base: NaOH, KOH,Ca(OH)₂ etc.
Salt: NaCl, AICI₃, CuSO₄ etc.

Non-electrolytes: The compounds which do not conduct electricity in molten state or in solution are called non-electrolytes. Non-electrolytes do not form ions in molten state or in solution.

Example: pure water, glucose, urea etc.

Wbbse Class 10 Physical Science Solutions

Question 2. Discusscs.

Answer:

The important characteristics of electrolytic substance:

1. Electrolytes dissociate into ions in their molten state or in solution. The cations and anions produced due to ionization move randomly in the solution.
2. Due to the presence of ions, the solution of an electrolyte can conduct electricity.
3. The conductivity of an electrolytic solution depends on the following factors- nature of electrolyte, concentration of solution and temperature.

Question 3. Classify the following substances as electrolytes and non electrolytes-sugar solution, fused sodium chloride, liquid HCI, mercury, kerosene, fused KCI, aqueous solution of sodium chloride.

Answer:

Electrolytes	Non-electrolytes
Fused sodium chloride, fused KCI, and aqueous solution of sodium chloride.	Sugar solution, mercury, liquid HCI, kerosene.

Question 4. State the differences between electrolytes and non-electrolytes.

Answer:

The differences are listed below:

Electrolytes	Non-electrolytes
Almost all ionic compounds and some polar covalent compounds act as electrolytes.	Non-electrolytes are mainly covalent compounds.
Electrolytes are soluble in polar solvents, e.g. water.	Non-electrolytes are generally soluble in non-polar solvents. Exception— glucose, sugar etc.
They produce ions in a molten state or in solution.	They do not produce ions either in molten state or in solution.
These substances conduct electricity in molten state or in solution.	Solution of non-electrolytes are non-conductors of electricity.
These substances undergo chemical changes during electrolysis.	These are non-conductors, so do not undergo chemical change during electrolysis.

 

Wbbse Class 10 Physical Science Solutions

Question 5. Describe the major differences in conduction of electricity by a metallic conductor and a solution of an electrolyte.

Answer:

The major differences are:

Metallic conductor	Electrolyte
During the conduction of electricity through a metallic conductor only physical changes take place in the conductor.	During conduction of electricity, an electrolyte undergoes chemical change to produce new substances.
Free electrons conduct electricity.	Cations and anions produced by the electrolyte conduct electricity.
Metallic conductors conduct electricity both in solid or liquid states e.g. mercury.	Electrolytes conduct electricity only in molten state or in solution.
The atoms do not change their positions during the conduction of electricity.	Ions migrate towards the electrodes to conduct electricity.
With increasing temperature, resistance of metallic conductor increases and hence Hurtiwity decreases.	With increasing temperature electrolytes increases.
The conductivity of metalic conductors are higher than that of electrolytes.	Electrolytic solutions generally have low conductivity compared to metalic conductors.

Question 6. Discuss the factors on which tonductance of an electrolyte depends.

Answer:

Conductance of electrolyte depends on:

1. Nature of electrolyte: A strong electrolyte dissociates almost completely in solution and hence the solution contains large number of ions. So the conductance of strong electrolytes is generally higher. On the other hand, a weak electrolyte dissociates only partially and hence it produces less number of ions in the solution. Therefore, the solution of a weak electrolyte conducts less electricity.

2. Concentration of solution: Higher the concentration of a solution, more ions will be produced in the solution and hence the conductance will increase.

3. Temperature: With increasing temperature kinetic energy of ions increases and hence cations and anions move quickly towards the electrodes. This increases the conductance of the solution.

Question 7. What is degree of dissociation? How is conductance of an electrolyte related to its degree of dissociation?

Answer:

Degree of dissociation

1. The fraction of total number of moles of an electrolyte that dissociates in solution or in molten state is known as degree of dissociation of that electrolyte. Degree of dissociation of strong electrolytes is high and that of weak electrolytes is low.
2. With an increase in the degree of dissociation, the conductance of an electrolyte increases.

Wbbse Class 10 Physical Science Solutions

Question 8. Why do electrolytes conduct electricity only in solution or in molten state but not in solid state?

Answer: Electrolytic substances are generally crystalline solids at normal conditions. In a crystalline state, the cations and anions are strongly held together by the electrostatic force of attraction.

As the ions cannot move in a solid state they cannot conduct electricity. In solution, the ions are separated and the force of attraction becomes weak. Hence the mobility of the ions increases. As a result, the solution conducts electricity.

Question 9. Among mercury and acidified water which one is an electrolyte and why?

Answer: Although mercury conducts electricity in liquid state, yet it is not termed as an electrolyte. Because mercury is an element and no chemical changes occur during conduction of electricity through it.

On the other hand during electrical conduction of acidified water, it chemically decomposes and produces hydrogen and oxygen at cathode and anode respectively. That is why it is called an electrolyte.

Examples of Physical Properties of Elements

Question 10. Hydrogen chloride can not conduct electricity in its liquid state whereas sodium chloride can conduct electricity in its fused state—explain.

Answer: Being a covalent compound hydrogen chloride does not ionise in liquid state. it exists as a molecule and acts as a non-electrolyte. Hence liquid HCI can not conduct electricity.

On the other hand, sodium chloride is an ionic compound and ionises in the fused state to form Na^⊕ and Cl^Θ ions. Due to the presence of such ions, it is considered as an electrolyte and can conduct electricity.

Question 11. An aqueous solution of HCI conducts electricity although it is a covalent compound—explain. Why CCl₄ is not an electrolyte?

Answer:

1. Hydrogen chloride (HCI) is a covalent gaseous substance that can not conduct electricity. But in aqueous solution HCI ionises to form H₃O(hydronium ion) and Cl^– ion-

\(\mathrm{HCl}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_3 \mathrm{O}^{+}+\mathrm{Cl}^{-}\)

Due to presence of such ions aqueous solution of HCI conducts electricity.

2. Carbon tetrachloride (CCI₄), being a covalent compound does not dissociate into ions and hence can not conduct electricity.

Wbbse Class 10 Physical Science Solutions

Question 12. Define strong electrolyte and weak electrolyte. Give example.

Answer: The electrolytes which dissociates almost completely in solution are called strong electrolytes. Acids like HCI, H₂SO₄ bases like NaOH, KOH and salts like NaCI, KCI, CaCl₂ etc act as strong electrolytes.

The electrolytes which dissociate partially in solution and most of the molecules remain undissociated are called weak electrolytes etc., Weak acids like H₂CO₃, HCOOH, CH₃COOH etc.., and weak bases like NH₄OH, Mg(OH)₂ etc., are examples of weak electrolyte.

Question 13. State the differences between a strong electrolyte and a weak electrolyte.

Answer:

The major differences are listed below:

Characteristic	Strong Electrolyte	Weak
Conductance	These substances are good conductors of electricity.	Conductance is relatively low as compared to strong electrolytes.
Number of ions in solution	These substances dissociate almost completely in solution and hence produce large number of ions.	These substances dissociate only partially and hence the number of ions produced in solution is relatively less.
Nature	These are generally ionic compounds. Example—NaCI, NaOH etc.  Exception—HCI is a covalent compound. However it is a strong electrolyte.	These are generally covalent compounds. Example—ammonia (NH3); acetic acid (CH3COOH) etc.
Constituent particles in solution	The solution only contains ions.	The solution contains ions as well as undissociated molecules.

Question 14. Explain why NaOH is a strong electrolyte but NH₄OH is a weak electrolyte.

Answer: In molten state or in aqueous solution, NaOH dissociates almost completely to give Na⁺ and OH^– ions. Due to the presence of greater number of ions in the solution, the conductivity of NaOH solution is high. Hence, NaOH is a strong electrolyte.

\(\mathrm{NaOH} \rightarrow \mathrm{Na}^{+}+\mathrm{OH}^{-}\)

On the other hand, NH₄OH dissociates partially in solution and most of the molecules remain undissociated. As a result, the number of ions present in NH₄OH solution is less. Hence, it is a weak electrolyte.

\(\mathrm{NH}_4 \mathrm{OH} \rightleftharpoons \mathrm{NH}_4^{+}+\mathrm{OH}^{-}\)

Wbbse Class 10 Physical Science Solutions

Question 15. A metal undergoes physical changes during conduction of electricity—explain with example.

Answer:

A metal undergoes physical changes during conduction of electricit

When electricity is passed through a metallic conductor, it becomes hot. This is known as heating effect of electricity. Sometimes the metal glows due to conduction of electricity.

For example, if electricity is passed through a tungsten filament of an electric bulb, the filament gets illuminated and radiates light. When the flow of electricity is stopped, the filament comes back to its initial state. Thus, it is a physical change.

Question 16. What is electrode? What is cathode and anode?

Answer:

Electrode: Two metallic (eg: Cu or Ag) or non-metallic (eg: graphite, gas carbon) rods that are partially immersed in the electrolytic solution or fused electrolyte are known as electrodes. When the electrodes are connected with the battery electricity passes through the electrolytes.

Cathode: The electrode which is connected with the -ve end of a battery is called cathode. During electrolysis reduction occurs here.
Anode:The electrode which is connected with the +ve end of a battery is termed as anode. During electrolysis oxidation occurs here.

Question 17. Define electrolysis. Is electrolysis of fused wax possible?

Answer:

Electrolysis:

The process by which an electrolyte in its molten state or in solution dissociates into its constituent ions on passing electricity through it, is known as electrolysis. Electrolysis of fused wax is not possible as wax is not an electrolyte.

Question 18. Write the differences between cathode and anode.

Answer:

The major differences between cathode and anode are listed below:

Cathode	Anode
Cathode is connected to the negative end of the battery.	Anode is connected to the positive end of the battery.
Cations are released at cathode.	Anions are released at anode.
At the cathode, cations are reduced to free atom by accepting electrons.	At anode, anions give up electrons and are oxidised to free atoms or radicals.

Question 19. Is electrolysis of an element possible? Justify.

Answer:

During electrolysis, a substance is decomposed to produce new substances when electricity is passed through the molten state or solution of the substance in an appropriate solvent. In solution, the process of electrolysis takes place due to the presence of cations and anions formed by the dissociation of the electrolyte.

Obviously, the electrolyte must produce oppositely charged ions in solution Elements do not dissociate into oppositely charged ions. Hence electrolysis of an element is not possible.

Question 20. Describe the ionic theory of electrolysis.

Answer:

The ionic theory of electrolysis:

Electrolytes dissociate into ions in a molten state or in solution. When electricity is passed through the solution, cations move towards the cathode and anions move towards the anode. At the cathode, cations accept electrons and form neutral atoms or radicals.

Similarly anions, at the anode, give up electrons to form neutral atoms or radicals. For example, when molten NaCI is electrolysed using a graphite anode and iron cathode, chlorine gas is produced at anode and metallic sodium is deposited at cathode.

\(\mathrm{NaCl} \rightarrow \mathrm{Na}^{+}+\mathrm{Cl}^{-}\)

At cathode: \(\mathrm{Na}^{+}+e \rightarrow \mathrm{Na}\)

At anode: \(\mathrm{Cl}^{-} \rightarrow \mathrm{Cl}+e ; \mathrm{Cl}+\mathrm{Cl} \rightarrow \mathrm{Cl}_2\)

Question 21. During electrolysis, the solution of an electrolyte contains large number of cations and anions. Yet the solution remains neutral—explain.

Answer: Electrolytes dissociate into cations and anions in their molten state or in solution. The number of cations present in the solution at any moment may not be equal to the number of anions. But the total positive charge carried by the cations and total negative charge of the anions are equal. For example, dissociation of one molecule of Na₂SO₄ gives two Na⁺ ions and one 4SO^2- ion.

Here, total positive charge = 2 x (+1) = +2 and total negative charge = 1 x (-2) = -2 . Again, during electrolysis, the number of electrons accepted by the cations per second at cathode is equal to the number of electrons lost by the anions per second at anode. Thus, at any moment, total positive charge in the solution is equal to total negative charge and hence electrical neutrality of the solution is maintained.

Chemical Properties of Metals vs. Nonmetals

Question 22. Electrolysis is basically a redox reaction—justify the statement.

Answer: According to the electronic theory of oxidation and reduction, oxidation is a process of loss of one or more electrons by an atom or ion and reduction is the gain of one or more electron(s) by an atom or ion.

When electricity is passed through the solution of an electrolyte, cations produced due to dissociation of the electrolyte move towards the cathode while anions move towards the anode. At the cathode, cations accept electrons and form neutral atoms or radicals.

So, we can say that the cations are reduced at the cathode. Similarly anions, at the anode, give up electrons to form neutral atoms or radicals. So, anions undergo oxidation at anode. Therefore, we can say that electrolysis is an oxidation-reduction reaction or redox reaction.

Question 23. Discuss the principle of electrolysis of acidified water using platinum electrodes with equations.

Answer:
Principle: Pure water is a non-conductor of electricity. But if a few drops of acid (H₂SO₄) is added to water, it becomes a good conductor. In this condition, water molecules ionize to produce H⁺ and OH^– ions.

\(\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}^{+}+\mathrm{OH}^{-}\)

Electrolyte: Water containing trace amount of H₂SO₄.
Electrodes: Cathode and anode made of platinum.

Cathode reaction: When electricity is passed through acidified water, H⁺ ions move towards the cathode. At cathode, an H⁺ ion accepts one electron and forms H-atom. H-atoms being unstable, combine with each other to form diatomic H₂ molecules. As a result, hydrogen gas is liberated at cathode.

\(\mathrm{H}^{+}+e \rightarrow \mathrm{H}, \mathrm{H}+\mathrm{H} \rightarrow \mathrm{H}_2 \uparrow\)

Anode reaction: On passing electricity, OH^– ions move towards the anode. At anode, each OH^– ion releases an electron to form OH radical. These OH radicals then combines together to form H₂O and oxygen (O₂). As a result oxygen gas is liberated at the anode.

\(\mathrm{OH}^{-} \rightarrow \mathrm{OH}+e, 4 \mathrm{OH} \rightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2 \uparrow\)

At a given temperature and pressure, the volume of hydrogen gas produced at the cathode is twice the volume of oxygen gas produced at the anode.

Question 24. How do you identify the gases formed by the electrolysis of water?

Answer: The gases formed at the cathode and anode can be identified in the following way:

1. When a burning stick is introduced into the gas accumulated at the cathode, the fire in the stick extinguishes but the gas burns with a bluish flame. This indicates that the gas is hydrogen.
2. When a burning stick without a flame is introduced into the gas accumulated at the anode, the stick catches fire and burns strongly with a flame but the gas itself does not burn. This indicates that the gas formed at anode is oxygen.

Question 25. Describe the electrolysis of CuSO₄ solution using platinum electrode.

Answer: The ionisation process occurred in aqueous solution of CuSO₄ is:

\(\mathrm{CuSO}_4 \rightarrow \mathrm{Cu}^{2+}+\mathrm{SO}_4^{2-}\) \(\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}^{+}+\mathrm{OH}^{-}\)

Since the tendency of accepting electron is greater in case of Cu²⁺ ion than H⁺ ion, Cu²⁺ ions move towards Pt-cathode, during electrolysis and deposited as metallic Cu by accepting two electrons at the cathode.

On the other hand tendency of losing electron is greater in case of OH^– ion than 4SO^2- ion.
Hence OH^– ions moves towards Pt-anode and get neutralised by losing electron to form OH radical. These OH radicals react with each other to form H₂O and O₂.

Reaction at cathode: \(\mathrm{Cu}^{2+}+2 e \rightarrow \mathrm{Cu}\)

Reaction at anode: \(\mathrm{OH}^{-} \rightarrow \mathrm{OH}+e ;\), \(4 \mathrm{OH} \rightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2 \uparrow\)

H⁺ and 4SO^2- ions remain in the solution. Hence the residual solution becomes acidic in nature.

Question 26. Describe the process, of electrolysis of aqueous solution of copper sulphate (CuSO₄) using copper electrodes.

Answer:

Electrolyte: An aqueous solution of copper sulphate (CuSO₄).
Electrode: Both cathode and anode are made of copper.
In aqueous solution, CuSO₄ dissociates into Cu²⁺ and 4SO^2- ions. Water molecules also dissociate partially to produce H⁺ and OH^– ions.

\(\mathrm{CuSO}_4 \rightleftharpoons \mathrm{Cu}^{2+}+\mathrm{SO}_4^{2-}\) \(\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}^{+}+\mathrm{OH}^{-}\)

Cathode reaction: When electricity is passed through the solution, both Cu²⁺ and H⁺ ions are migrated towards the cathode. As tendency of Cu²⁺ ions to discharge at cathode is more than H⁺ ions, it accepts 2 electrons to form Cu-atom. The produced atoms are deposited at cathode and hence the mass of cathode increases.

\(\mathrm{Cu}^{2+}+2 e \rightarrow \mathrm{Cu} \text { (reduction) }\)

 

Anode reaction: Though both the anions present in the solution are migrated towards the anode, neither of them is discharged, instead, Cu-atoms from the anode are oxidised to Cu²⁺ ions, which dissolves in the solution. Thus, the anode plate begins to erode gradually.

\(\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+}+2 e \text { (oxidation) }\)

At any instant, the amount of Cu deposited at cathode is equal to the amount of Cu dissolved in the solution from anode. Hence, the concentration of Cu²⁺ ions in solution does not change.

Question 27. During electroplating, DC of low intensity should be applied for longer period of time. Explain. What will happen if AC is applied instead Of DC?

Answer: During electroplating, DC current of low intensity is applied for a longer period of time. Due to low supply of current, the solution does not become hot. At the same time, it helps in the formation of a uniform coating over the article.

If AC is applied instead of DC, the electrodes continuously change their nature. As a result, movement of ions in solution is restricted and electrolysis does not take place. Hence, alternating current is not suitable for electroplating.

Applications of Electric Current in Chemical Processes

Question 28. During electrolysis of CuSO₄ solution using Cu-electrodes, the mass of anode gradually decreases while the mass of cathode increases. Explain.

Answer: Aqueous solution of CuSO₄ contains Cu²⁺ and H⁺ ions as cations and 4SO^2- and OH^– ions as anion. When aqueous solution of CuSO₄ is electrolysed using Cu-electrodes, the Cu²⁺ ions are preferably discharged over H⁺ ions at the cathode. Consequently Cu²⁺ ions accept electrons to form Cu-atoms, which deposit over the cathode.

Hence, the mass of the cathode increases. On the other hand, the copper rod acts as an anode. At the anode, each copper atom loses two electrons to form Cu²⁺ ions, which go into the solution. So, the anode is gradually dissolved into the solution and its mass decreases.

Cathode reaction:\(\mathrm{Cu}^{2+}+2 e \rightarrow \mathrm{Cu}\)

Anode reaction: \(\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+}+2 e\)

Question 29. Does the concentration of the solution change during electrolysis of CuSO₄ solution using Gu-electrodes?

Answer: During electrolysis of an aqueous solution of CuSO₄ using Cu-electrodes, at any moment the amount of copper deposited at cathode is equal to the amount of copper brought into solution from the anode. Hence, the concentration of Cu²⁺ ions in solution remains the same. So, the colour of the solution also does not change.

Cathode reaction: \(\mathrm{Cu}^{2+}+2 e \rightarrow \mathrm{Cu}\)

Anode reaction: \(\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+}+2 e\)

Electric Current And Chemical Reactions Topic A Electrolyte And Electrolysis Very Short Answer Type Questions Choose The Correct Answer

Question 1. Electrolytes conduct electricity in

1. Solid state
2. Molten state
3. Aqueous solution
4. Both 2 and 3

Answer: 4. Both 2 and 3

Question 2. An example of a strong electrolyte is

1. H₂CO₃
2. HNO₃
3. NH₄OH
4. HCOOH

Answer: 2. HNO₃

Question 3. An example of an inorganic salt which acts as a weak electrolyte is

1. KNO₃
2. ZnCl₂
3. CaCl₂
4. Ca₃(PO₄)₂

Answer: 4. Ca₃(PO₄)₂

Question 4. The aqueous solution of a weak electrolyte contains

1. Only molecules
2. Only ions
3. Both ions and molecules
4. None of these

Answer: 3. Both ions and molecules

Question 5. The solution of a non-electrolyte contains

1. Only molecules
2. Only ions
3. Both ions and molecules
4. None of these

Answer: 1. Only molecules

Question 6. Which of the following is a non-electrolyte?

1. Acetic acid
2. Carbonic acid
3. Chloroform
4. Formic acid

Answer: 3. Chloroform

Question 7. With the rise in temperature, the conductance of a metallic conductor

1. Increases
2. Decreases
3. Remains unchanged
4. May either increase or decrease

Answer: 2. Decreases

Question 8. When an aqueous solution of an electrolyte is heated, the velocity of ions in the solution

1. Decreases
2. Increases
3. Either decreases or increases
4. Remains unchanged

Answer: 2. Increases

Question 9. The conductance of metallic conductors when compared to that of electrolytes is

1. Low
2. High
3. Either low or high
4. Equal

Answer: 2. High

Question 10. During electrolysis, the temperature of the electrolyte

1. Increases
2. Decreases
3. Shows no change
4. Either increases or decreases

Answer: 1. Increases

Question 11. Which of the following compounds containing-OH group acts as an electrolyte?

1. Phenol (C₆H₅OH)
2. Methanol (CH₃OH)
3. Ethanol (C₂H₅OH)
4. 2-propanol (CH₃CHOHCH₃)

Answer: 1. Phenol (C₆H₅OH)

Question 12. Which of the following compounds does not conduct electricity in its solid state?

1. NaCI
2. PbBr₂
3. Ice
4. All of these

Answer: 4. All of these

Question 13. Aqueous solution of which of the following compounds contains both ions and molecules of the compound?

1. NaCI
2. CH₃COOH
3. CH₃CH₂OH
4. CHCI₃

Answer: 2. CH₃COOH

Question 14. Which of the following compounds is not an electrolyte?

1. NaCI
2. H₂SO₄
3. KOH
4. Glucose

Answer: 4. Glucose

Question 15. Which of the following compounds is an electrolyte?

1. Urea (H₂NCONH₂)
2. Ethanol (C₂H₅OH)
3. Acetic acid (CH₃COOH)
4. Distilled water

Answer: 3. Acetic acid (CH₃COOH)

Question 16. Which of the following pairs of bases acts as weak electrolytes?

1. Mg(OH)₂,Fe(OH)₂
2. KOH, NH₄OH
3. NaOH, Mg(OH)₂
4. NaOH, KOH

Answer: 1. Mg(OH)₂,Fe(OH)₂

Question 17. The ratio of the mass of hydrogen to oxygen produced during electrolysis of water, is

1. 1:8
2. 2:1
3. 2:3
4. 3:1

Answer: 1. 1:8

Question 18. The ions discharged at the anode during the electrolysis of dilute and concentrated HCI are respectively

1. OH^–   & Cl^– 
2. Cl^–  & OH^–  
3. Cl^–  in both cases
4. OH^– in both cases

Answer: 1. OH^–   & Cl^– 

Question 19. The relative tendency of an ion to discharge at a particular electrode depends on the

1. Position of the ion in the electrochemical series
2. Concentration of the ion in the solution
3. Nature of the electrode
4. All of these

Answer: 4. All of these

Question 20. During electrolysis of CuS04 solution using Pt-electrode

1. The anode gradually dissolves into the solution while cathode becomes thicker
2. The anode becomes thicker while the cathode gradually dissolves into the solution
3. Both cathode and anode become thicker
4. Both cathode and anode remain unchanged

Answer: 4. Both cathode and anode remain unchanged

Question 21. Which has the maximum tendency to get reduced at the cathode?

1. K⁺
2. Na⁺
3. H⁺
4. Ag⁺

Answer: 4. Ag⁺

Question 22. Which of the following cations does not exist in free state in its aqueous solution?

1. H⁺
2. Na⁺
3. K⁺
4. Cu²⁺

Answer: 1. H⁺

Question 23. The metal which can be extracted by electrolysis of its molten salt is

1. Fe
2. AI
3. Cu
4. Ag

Answer: 2. AI

Question 24. Electrolysis of which of the following aqueous solutions will discharge the corresponding metal at the cathode?

1. NaCl
2. KCI
3. CuSO₄
4. AICI₃

Answer: 3. CuSO₄

Question 25. When CuSO₄ solution is electrolysed using copper electrodes, blue colour of solution

1. Deepens
2. Fades
3. Remains unchanged
4. Becomes colourless

Answer: 3. Remains unchanged

Question 26. When CuSO₄ solution is electrolysed using Pt-electrodes, product obtained at anode is

1. Cu
2. Cu²⁺
3. O₂
4. H₂

Answer: 3. O₂

Question 27. When CuSO₄ solution is electrolysed using either copper or Pt-electrodes, the product obtained at the cathode is

1. H₂
2. Cu
3. O₂
4. Cu²⁺

Answer: 2. Cu

Question 28. Aqueous solution of which one is an weak electrolyte?

1. CH₃COOH
2. NaOH
3. H₂SO₄
   
4. NaCl

Answer: 1. CH₃COOH

Question 29. Which one of the following can conduct electricity?

1. Fused NaCl
2. Liquid HCI
3. Solid NaCl
4. Aqueous solution of glucose

Answer: 1. Fused NaCl

Question 30. Which of the following is an electrolyte?

1. Mercury
2. Aqueous solution of sugar
3. Salt solution
4. Bromine water

Answer: 3. Salt solution

Question 31. 1.12 L of a gas is formed at cathode in the electrolysis of water. The amount of gas formed at anode at same temperature and pressure will be

1. 5.6 L
2. 11.2 L
3. 22.4 L
4. 44.8 L

Answer: 1. 5.6 L

Question 32. Which of the following reaction occurs at anode during the electrolysis of CuSO₄ using Cu-electrode?

1. \(4 \mathrm{OH}^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2+4 e\)
2. \(\mathrm{Cu}^2+2 e \rightarrow \mathrm{Cu}\)
3. \(2 \mathrm{H}^{+}+2 e \rightarrow \mathrm{H}_2\)
4. \(\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+}+2 e\)

Answer: \(\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+}+2 e\)

Question 33. The container or the vessel where electrolysis is done is termed as

1. Voltameter
2. Ammeter
3. Thermometer
4. Voltmeter

Answer: 1. Voltameter

Question 34. During electrolysis the reaction occurs at anode is

1. Oxidation
2. Reduction
3. Substitution
4. None of these

Answer: 1. Oxidation

Question 35. Which of the following is formed at cathode during electrolysis of aqueous NaCI solution?

1. Na
2. H₂
3. Cl₂
   
4. O₂

Answer: 2. H₂

Question 36. Which of the following is formed at anode during electrolysis of water?

1. H₂S
2. H₂
3. O₂
4. H₂O₂

Answer: 3. O₂

Wbbse Class 10 Current Electricity Questions And Answers

Question 37. During electrolysis of CuSO₄  solution using Cu-electrode

1. No change in concentration of CuSO₄ occurs
2. Concentration of CuSO₄ in solution increases
3. Concentration of CuSO₄ in solution first increases and then decreases
4. Concentration of CuSO₄ in solution first decreases and then increases.

Answer: 1. No change in concentration of CuSO₄ occurs

Question 38. Which of the following energy conversion takes place during electrolysis?

1. Chemical energy → electrical energy
2. Chemical energy → sound energy
3. Electrical energy → chemical energy
4. Electrical energy → light energy

Answer: 3. Electrical energy → chemical energy

Question 39. Nature of the current used in electrolysis is

1. DC
2. AC
3. DC or AC
4. Not specific

Answer: 1. DC

Question 40. The nature of the residual solution during electrolysis of aqueous solution of CuS04 using Pt-electrode is

1. Neutral
2. Acidic
3. Basic
4. Firstly acidic and then basic

Answer: 2. Acidic

Question 41. Which of the following is not a characteristic of electrolysis?

1. DC is used in electrolysis
2. Ions of the electrolyte conduct electricity
3. Metallic ions are reduced and non metallic ions are oxidised
4. Oxidation takes place at cathode and reduction takes place at anode

Answer: 4. Oxidation takes place at cathode and reduction takes place at anode

Question 42. During electrolysis, electricity is conducted by

1. Free electrons
2. Ions
3. Metal
4. Non-metal

Answer: 2. ions

Electric Current And Chemical Reactions Topic A Electrolyte And Electrolysis Answer In brief

Question 1. What do you mean by conductors of electricity?
Answer:

Conductors of electricity

Substances through which electricity can pass are called conductors of electricity. For example—different metals.

Question 2. What do you mean by non-conductors of electricity or insulators?
Answer:

Non-conductors of electricity or insulators

Substances through which electricity cannot pass are called non-conductors of electricity or insulators. For example—wood, glass etc.

Question 3. Name a non-metallic solid element which is a non-conductor of electricity.
Answer: Sulphur.

Question 4. Between NaCI and HCI, which one is a nonelectrolyte in its pure state?
Answer: HCI.

Common Misconceptions About Electric Current and Reactions

Question 5. Name an organic compound which can conduct electricity in its aqueous solution. Or, Give example of a compound whose aqueous solution is an weak electrolyte.
Answer: Acetic acid (CH₃COOH)

Wbbse Class 10 Current Electricity Questions And Answers

Question 6. Name a liquid which can conduct electricity though it is not an electrolyte.
Answer: Mercury.

Question 7. Name an compound.
Answer: Silica (SO₂)

Question 8. Name a liquid element which is a nonconductor of electricity.
Answer: Bromine.

Question 9. Name a non-metallic substance which can conduct electricity but does not ionise. Or, Give example of a non electrolytic conductor of electricity.
Answer: Graphite.

Question 10. State whether an aqueous solution of sugar containing small amount of salt will conduct electricity or not.
Answer: An aqueous solution of sugar cannot conduct electricity but an aqueous solution of salt is an electrolyte. Hence, the aqueous solution of sugar containing a pinch of salt will conduct electricity.

Question 11. Give an example of a non-metallic cation.
Answer: Ammonium ion (NH₄⁺).

Question 12. Give an example of a liquid non-electrolyte compound which is soluble in water.
Answer: Ethyl alcohol.

Question 13. What are the constituents of the solution of a strong electrolyte?
Answer: The solution of a strong electrolyte contains cations and anions formed by the dissociation of the electrolyte. As a strong electrolyte dissociates completely, there is no undissociated molecules of the electrolyte in the solution.

Question 14. What are the constituents of the solution of a weak electrolyte?
Answer: The solution of a weak electrolyte contains cations and anions formed by the dissociation of the electrolyte along with the undissociated molecules of the electrolyte.

Question 15. Identify the strong electrolytes and weak electrolytes from the given compounds— fused NaOH, aqueous solution of KCl, H₂CO₃, CH₃COOH, HCN, ZnSO₄ solution, Al(OH)₃.
Answer:
Strong electrolytes: Fused NaOH, aqueous solution of KCl, and ZnSO₄ solution.
Weak electrolytes: H₂CO₃,CH₃COOH, HCN, Al(OH)₃.

Question 16. Give an example of a weak electrolytic salt.
Answer: Sodium carbonate (Na₂CO).

Question 17. Is the number of cations and anions formed due to the dissociation of an electrolyte always equal?
Answer: The number of cations in the solution of an electrolyte may or may not be equal to the number of anions. For example, in case of NaCI, it is same whereas, for Na₂SO₄, it is not.

Wbbse Class 10 Current Electricity Questions And Answers

Question 18. How the degree of dissociation of an weak electrolyte can be increased?
Answer: Degree of dissociation of a weak electrolyte can be increased up to a certain limit by diluting the solution of the weak electrolyte.

Question 19. Liquids like benzene, chloroform do not conduct electricity. Why?
Answer: Chloroform or benzene exists in liquid state, but they do not dissociate into cations and anions. Thus, they cannot conduct electricity.

Question 20. Though HCI is a covalent compound, it acts as a strong electrolyte in aqueous solution. Explain with reasons.
Answer: HCI is a covalent compound. But, HCI molecule is polar and it ionises in polar solvent like water to produce hydronium ion (H₃O⁺) and chloride ion (Cl^–  ).

\(\mathrm{HCl}+\mathrm{H}_2 \mathrm{O} \rightleftharpoons \mathrm{H}_3 \mathrm{O}^{+}+\mathrm{Cl}^{-}\)

Due to the presence of these ions in aqueous solution, HCI acts as a strong electrolyte.

Question 21. What is a voltameter?
Answer:

Voltameter

The apparatus in which the electrolysis of an electrolyte is carried out is known as a voltameter. It consists of a vessel (generally made of glass or fibre) in which the electrolytic solution is taken along with the corresponding electrodes.

Question 22. What is electrolytic dissociation?
Answer:

Electrolytic dissociation

Electrolytic substances dissociate spontaneously in molten state or in solution partially or completely to form their constituent ions. This phenomenon is known as electrolytic dissociation.

Question 23. Which type of current is used in electrolysis?
Answer: Direct current or DC.

Question 24. In which direction does the current flow through the electrolytic solution during electrolysis?
Answer: During electrolysis, electric current flows from the battery to the anode and again passes into the battery through the cathode.

Question 25. State whether electrolysis will take place if alternating current (AC) is passed through an electrolytic solution?
Answer: No, electrolysis will not take place.

Question 26. Which energy is responsible for chemical reaction occurring during electrolysis?
Answer: Electrical energy.

Question 27. Which is responsible for conducting of electricity during electrolysis of electrolytes?
Answer: Corresponding cations and anions of the electrolyte.

Question 28. Where do the cations migrate during electrolysis?
Answer: Towards the cathode.

Question 29. Where do the anions migrate during electrolysis?
Answer: Towards the anode.

Question 30. Mention the volumetric ratio of the gases produced at the cathode and anode during electrolysis of acidified water.
Answer: 2:1.

Wbbse Class 10 Current Electricity Questions And Answers

Question 31. Which metal is used as cathode during electrolysis of water?
Answer: Platinum (Pt) metal.

Question 32. Between Na+ and Na, which one is more stable?
Answer: Na⁺ ion.

Question 33. Which substance is formed at anode during electrolysis of concentrated NaCI solution?
Answer: Chlorine gas.

Question 34. Which one of OH^– and Na⁺ ion will be neutralised at anode?
Answer: OH^– ion.

Question 35. Which one of Cu²⁺ and H⁺ ion has the higher tendency to be neutralised at cathode?
Answer: Cu²⁺ ion.

Question 36. What can be observed during electrolysis of CuSO₄ using Cu-electrode?
Answer: Cu-anode gets thinner while Cu-cathode gets thicker.

Question 37. What happens to the colour of the solution when an aqueous solution of CuSO₄ is electrolysed using Pt-electrodes?
Answer: The blue colour of the solution gradually fades away.

Question 38. What happens to the colour of the solution when an aqueous solution of CuSO₄ is electrolysed using Cu-electrodes?
Answer: The blue colour of the solution remains unchanged.

Question 39. Which ions are present in an aqueous solution of CuSO₄?
Answer: Cu²⁺, 4SO^2-, H⁺ and OH^–.

Electric Current And Chemical Reactions Topic A Electrolyte And Electrolysis Fill In The Blanks

Question 1. Electrolytic compounds are generally ________ in nature.
Answer: Ionic

Question 2. Generally, ________ compounds are non-electrolytes.
Answer: Covalent

Question 3. The gas produced at _____ during electrolysis of water burns with a bluish flame.
Answer: Cathode

Question 4. The conductivity of water increases on the addition of a small amount of _______ or ______
Answer: Acide, base

Question 5. _______ is a non-metal that can be used as electrode.
Answer: Graphite

Question 6. At the cathode, cations get _______ by accepting _______
Answer: Reduced, electron

Question 7. At the anode, anions get _______ by releasing ________
Answer: Oxidised, electron

Wbbse Class 10 Current Electricity Questions And Answers

Question 8. At the electrodes, ions lose their _______
Answer: Charge

Question 9. _______ is a covalent compound which acts as an electrolyte in its aqueous solution.
Answer: Hcl

Question 10. Strong electrolytes dissociate _______ to produce ions in aqueous solutions.
Answer: Completely

Question 11. In aqueous solution, very few molecules of a weak electrolyte undergo _______
Answer: Dissociation

Question 12. NaCI does not conduct electricity in _______ state.
Answer: Solid

Question 13. Electrolytes dissociate into their corresponding _______ in polar solvents.
Answer: Ions

Question 14. ________ are responsible for conduction of electricity through metals.
Answer: Free electrons

Question 15. _______ are not transferred during conduction of electricity through metals.
Answer: Atoms

Question 16. The ions ______ from one part of the solution to another part during electrolysis.
Answer: Move

Wbbse Class 10 Current Electricity Questions And Answers

Question 17. The _______ of the electrolyte is maintained at any instant during electrolysis.
Answer: Electrical neutrality

Question 18. The tendency of H⁺ ions to be discharged at the cathode is _______ than that of Na⁺.
Answer: Greater

Question 19. Electrolysis of a dilute aqueous solution of NaCI using mercury electrodes produces _______ at the cathode.
Answer: Sodium-amalgam

Question 20. In an electrolytic cell, _______ energy is converted into ________ energy.
Answer: Chemical, Electrical

Question 21. Electrolysis is a _______ process.
Answer: Redox

Question 22. In an electrolytic cell, the electric current flows from _______ to _______ within the electrolyte.
Answer: Cathode, anode

Question 23. HCI does not conduct electricity in _______ solvents.
Answer: Non-polar

Question 24. If an electrolyte is added to pure water, then its electrical conductivity ______ compared to that of pure water.
Answer: Increase

Question 25. During electrolysis of CuSO₄ solution using Cu electrodes, the ________ gets gradually eroded while the ________ becomes thicker.
Answer: Anode, cathode

Question 26. HCOOH is ________ electrolyte.
Answer: Weak

Question 27. Na⁺ is deposited at ______
Answer: Cathode

Wbbse Class 10 Current Electricity Questions And Answers

Question 28. _________ gas is formed at anode during electrolysis of water.
Answer: Oxygen

Question 29. _______ is formed at anode during electrolysis of copper sulfate solution using Cu-electrode.
Answer: Cu²⁺

Electric Current And Chemical Reactions Topic A Electrolyte And Electrolysis State Whether True Or False

Question 1. Electrolytes conduct electricity in solid state.
Answer: False

Question 2. H₂CO₃ is a strong electrolyte.
Answer: False

Question 3. The solution of a weak electrolyte contains both ions and molecules.
Answer: True

Question 4. With the rise in temperature, the conductance of an aqueous solution of an electrolyte remains unchanged.
Answer: False

Question 5. Distilled water conducts electricity.
Answer: False

Question 6. HCI is an electrolyte in its pure state.
Answer: False

Question 7. During electrolysis of acidified water, H2 gas is produced at the cathode.
Answer: True

Question 8. Electrolysis takes place if alternating current (AC) is passed through the solution.
Answer: False

Question 9. Reduction takes place at cathode whereas oxidation takes place at anode.
Answer: True

Question 10. Copper is an example of an inert electrode.
Answer: False

Wbbse Class 10 Current Electricity Questions And Answers

Question 11. During electrolysis of CuSO₄ solution using Cu electrodes, the anode gets gradually eroded while the cathode gets thicker.
Answer: True

Question 12. When CuSO₄ solution is electrolysed using Pt-electrodes, the blue colour of the solution remains unchanged.
Answer: False

Question 13. Mercury can conduct electricity but it is a non-electrolyte.
Answer: True

Question 14. The number of cations and anions present in an electrolyte is always equal.
Answer: False

Question 15. Voltameter is used to measure the potential difference between any two points of an electrical circuit.
Answer: False

Question 16. Lower the position of a metal in the electrochemical series, lower will be the tendency of the cations of that metal to get discharged at the cathode.
Answer: False

Question 17. Electrolytes conduct electricity through electron during electrolysis.
Answer: False

Question 18. CH₃COOH is a strong electrolyte.
Answer: False

Question 19. NH₄OH is weak electrolyte.
Answer: True

Wbbse Class 10 Current Electricity Questions And Answers

Question 20. H₂ gas is formed at cathode during electrolysis of aqueous solution of NaCI.
Answer: True

Question 21. O₂ gas is formed at cathode during electrolysis of water.
Answer: False

Question 22. Mass of the cathode gradually increases during electrolysis of copper sulfate solution (aqueous) using copper electrode.
Answer: True

Electric Current And Chemical Reactions Topic B Application Of Electrolysis Synopsis

1. The process of electrolysis is used in the extraction of metals, refining of metals and in electroplating.
2. When a molten mixture of alumina, cryolite and fluorspar is electrolysed using graphite as anode and gas carbon as cathode, pure aluminium is deposited at the cathode.

Electrorefining of copper is carried out by taking an aqueous solution of CuSO₄ containing small amount of H₂SO₄ as the electrolyte in a container coated with lead, the impure copper rod as anode and a thin plate of pure copper as cathode.

3. During electroplating, the object on which electroplating is to be done is taken as the cathode, a plate of pure metal to be deposited on the object is taken as the anode and an aqueous solution of a salt of the metal to be deposited is taken as the electrolyte.

Electric Current And Chemical Reactions Topic B Application Of Electrolysis Short And Long Answer Type Questions

Question 1. Mention the practical uses of electrolysis.

Answer:

Practical uses of electrolysis

1. Strong electro-positive metals like Na, K, Ca, Mg, Al etc are extracted using electrolysis.
2. Electrolysis is used in the purification process of some metals like Cu, Ag and Al.
3. Electrolysis is used in the industrial preparation of several substances like oxygen, chlorine, sodium hydroxide etc.
4. Electrolysis is used in the process of electroplating.

Question 2. What do you mean by the term ‘extraction of metal’? Which type of metals can be extracted by electrolytic reduction and why?

Answer:

‘Extraction of metal

1. Separation of a metal from its ores using a series of physical and chemical processes is known as extraction of metal. The processes are employed to obtain the pure metal by removing the impurities present in the ore of the metal.
2. Highly reactive metals like Na, K, Ca, Al, Mg etc., are extracted from their ores by electrolytic reduction. The oxides of these metals are highly stable and hence carbon reduction process is not suitable for extraction of these metals. Thus, they are extracted by electrolysis of their molten chloride salts or sometimes their molten oxides (e.g. Al).

Physical Science Class 10 West Bengal Board

Question 3. Describe the process of extraction of aluminium from alumina by electrolytic method.

Answer:

The process of extraction of aluminium from alumina by electrolytic method

Electrolyte used: A molten mixture of pure alumina (Al₂O₃), cryolite (Na₃AIF₆) and fluorspar ( CaF₂) is used as the electrolytic solution.

Voltameter and electrodes: An iron tank is used as container in which the electrolyte is taken. The inner walls of the container are lined with gas carbon which acts as cathode. Some graphite rods are partially immersed into the solution. These rods act as anode.

Process: In the tank, a molten mixture of the electrolyte containing 60% cryolite (Na₃AIF₆), 20% pure alumina(Al₂O₃) and 20% fluorspar (CaF₂) is taken. The melting point of pure alumina is 2050°C, but in the mixture the melting point decreases considerably to 900°C.

The surface of the electrolytic mixture is covered with powdered coke to prevent the oxidation and resulting corrosion of the graphite anode. Aluminium is liberated at the cathode in molten state which deposits at the bottom of the vessel from where it is taken out through the outlet. At anode, oxygen is produced. The aluminium thus obtained is about 99.95% pure.

Visual Representation of Chemical Reactions with Electric Current

Electrolytic dissociation: \(\begin{aligned}
& \mathrm{Al}_2 \mathrm{O}_3 \rightleftharpoons 2 \mathrm{Al}^{3+}+3 \mathrm{O}^{2-} \\
& \text { (molten) }
\end{aligned}\)

Cathode reaction: \(\mathrm{Al}^{3+}+3 e \rightarrow \mathrm{Al}\)

Anode reaction: \(3O^{2-} \rightarrow 3O+6 e\); \(3 \mathrm{O}+3 \mathrm{O} \rightarrow 3 \mathrm{O}_2 \uparrow\)

Question 4. Why is cryolite and fluorspar added to alumina during the extraction of aluminium by electrolytic method?

Answer: During electrolysis of aluminium by electrolytic method, cryolite and fluorspar are added to pure alumina because of the following:

1. Alumina has a melting point of about 2050°C. At such a high temperature, most of the aluminium produced is wasted due to evaporation. Also, it requires a large amount of electricity to carry out the reaction. When cryolite and fluorspar are added to pure alumina the melting point of the mixture drops to 900°C . Hence, the cost of production decreases.

2. Fluorspar decreases the viscosity of the solution. Therefore, ions can move freely in solution and the conductivity increases.

Word Problems Involving Electric Current and Chemical Reactions

Question 5. Electrolysis of acidified solution of CuS04 deposits Cu at cathode. But, electrolysis of acidified solution of an Al-salt does not deposit Al at cathode. Explain with reasons.

Answer: Acidified solution of CuSO₄ contains Cu²⁺ and H⁺ ions as cations. Tendency of Cu²⁺ ions to get discharged at cathode is more than that of H⁺ ions. Hence, Cu²⁺ ions migrate preferentially to cathode and accept electrons to form Cu-atoms.

On the other hand, aqueous solution of an Al-salt contains Al³⁺ and H⁺ ions. But, the tendency of H⁺ ions to get discharged at cathode is more than that of Al³⁺ ions. So, H⁺ ions migrate preferentially towards cathode and are reduced to H-atom. Hence, Al-atoms are not discharged at cathode.

Question 6. What do you mean by electrorefining of metals? Discuss the principle of electrolytic refining.

Answer:

Electrorefining of metals:

The process of removal of impurities from a metal extracted from its ore and its conversion to pure metal by electrolysis is known as electro-refining of metal.

Physical Science Class 10 West Bengal Board

In electrolytic refining, a block of impure metal is taken as an anode and a plate or rod of pure metal is taken as cathode. An aqueous solution of a salt of that metal is taken as an electrolyte. On electrolysis, metal atoms at anode are oxidized to ions and dissolve into solution. The cations of the metal are discharged at cathode and deposited on the cathode in pure state.

Question 7. Briefly describe the electrolytic refining of copper.

Answer:
Electrolyte: Aqueous solution of copper sulphate (CuSO₄) mixed with dilute H₂S0₄.
Electrodes: A thin plate of pure copper is used as the cathode and a plate of impure copper is used as the anode.

Process: The electrolyte is taken in a container lined with lead and electricity is passed through the solution. At anode (impure Cu block), Cu- atoms are oxidised to Cu^{2 +} ions and dissolves into the solution.

These Cu^{2 +} towards the cathode (pure Cu plate) and each accepts 2 electrons to form Cu-atom. The produced atoms are deposited at the cathode. The copper obtained in this method is almost 99.99% pure.

Electrolytic dissociation: \(\mathrm{CuSO}_4 \rightleftharpoons \mathrm{Cu}^{2+}+\mathrm{SO}_4^{2-}\)

Cathode reaction: \(\mathrm{Cu}^{2+}+2 e \rightarrow \mathrm{Cu}\)

Anode reaction: \(\mathrm{Cu} \rightarrow \mathrm{Cu}^{2+}+2 e\)

Question 8. What is important.

Answer:
1. During the electrorefining of copper, the more electropositive metals (Fe, Ni, Zn etc.) present as impurities in the impure copper anode, move into the solution and the less electropositive metals (Au, Ag, Pt etc.) deposit with other impurities below the anode as mud. This is known as anode mud.
2. Anode mud contains precious metals like gold, silver, platinum etc.

Physical Science Class 10 West Bengal Board

Question 9. What is electroplating? Describe the principle.

Answer:

Electroplating:

1. The process of formation of a uniform coating of a less reactive metal (such as iron, copper etc.) over a relatively more reactive metal (such as silver, gold, nickel etc.) by electrolytic method is known as electroplating.

2. The article which is to be electroplated is taken as cathode and a pure block of the metal which is to be used as coating is taken as anode. A solution of a water-soluble salt of the metal which is used as coating is taken as electrolytic solution.

For example, while a silver article is electroplated with gold, the silver article is taken as cathode, a block of pure gold is taken as anode and an aqueous solution of potassium aurocyanide is taken as the electrolytic solution.

Question 10. What are the purposes of electroplating?

Answer:

The purposes of electroplating:

1. A reactive metal or its alloys are easily attacked by atmospheric oxygen, water vapour or C02 and undergo corrosion. To prevent corrosion, the article is electroplated by a less reactive metal.
2. The physical appearance can be made more attractive by electroplating. For example, when silver jewellery are electroplated with gold, they become more attractive and beautiful.
3. Metal surface can be made more rigid and corrosion of metal due to friction can be avoided by electroplating.

Question 11. What precautions should be during electroplating?

Answer:

Precautions should be taken during electroplating

1. The concentration of metal ions in electrolytic solution should be high.
2. The solution should be of high conductivity.
3. The salt (electrolyte) should be stable, i.e., it should not react with air.
4. There should be considerable rate of dissolution at the anode so that concentration of the solution remains constant.
5. Direct current (DC) of low intensity should be applied to the solution for a longer period of time.
6. The metal surface on which the electroplating is to be done should be smooth and clean.

Wbbse Class 10 Current Electricity Questions And Answers

Question 12. Name the electrodes arid electrolytic solution used in electroplating an article with the following metals:
1. Copper, 2. Silver, 3. Tin, 4. Nickel, 5. Chromium, 6. Gold.

Answer: Answers are given in the given table:

The metal used for electroplating	Cathode	Anode (metal plate)	Electrolyte (aqueous solution)
1. Copper	The article which is to be electroplated	A thin plate of pure copper	Copper sulphate (CuSO4)
2. Silver		A thin plate of pure silver	Potassium argentocyanide K[Ag(CN)2]
3. Tin		A thin plate of pure tin	Stannous chloride ( SnCI2)
4. Nickel		A thin plate of pure nickel	Nickel sulphate (NiSO4)
5. Chromium		A thin plate of pure chromium	Chromic sulphate [Cr2(SO4)3] and chromic acid (H2CrO4)
6. Gold		A thin plate of pure gold	Potassium aurocyanide K[Au(CN)2]

 

Electric Current And Chemical Reactions Topic B Application Of Electrolysis Very Short Answer Type Questions Choose The Correct Answer

Question 1. The process of electrolysis is applied in

1. Electroplating
2. Electrorefining
3. Extraction of metals
4. All of these

Answer: 4. All of these

Physical Science Class 10 West Bengal Board

Question 2. During electroplating by nickel, the electrolyte used is

1. Ni Br₂ solution
2. NiSO₄.(NH₄)₂SO₄.6H₂O solution with small amount of H₂SO₄
   
3. Molten nickel oxide (NiO)
4. NiCI₂ solution

Answer: 2. NiSO₄.(NH₄)₂SO₄.6H₂O solution with small amount of H₂SO₄

Question 3. The objective of electroplating is to

1. Protect metallic object from weathering
2. Make the metallic object more attractive
3. Increase the metallic mass of the object
4. Both A and B

Answer: 4. Both A and B

Question 4. During the electroplating of an object by silver, a pure silver plate is used as the

1. Cathode
2. Anode
3. Either anode or cathode
4. Electrolyte

Answer: 2. Anode

Question 5. During electroplating, electrical conductivity of electrolytic solution used should be

1. High
2. Low
3. Moderate
4. Of any value

Answer: 1. High

Wbbse Class 10 Current Electricity Questions And Answers

Question 6. During electroplating

1. The cathode is eroded
2. The anode is eroded
3. Neither cathode nor anode is eroded
4. Both the electrodes are eroded.

Answer: 2. The anode is eroded

Question 7. Which is not present in the anode mud deposited during electrorefining of copper?

1. Au
2. Ag
3. Pt
4. Fe

Answer: 4. Fe

Question 8. During electrorefining of copper, the electrolyte used is

1. Pure CuSO₄ 
2. Aqueous solution of pure CuSO₄ 
3. Mixture of aqueous solution of CuS04 and small amount of H₂SO₄
4. None of these

Answer: 3. Mixture of aqueous solution of CuSO₄ and small amount of H₂SO₄

Question 9. Which of the following is used as cathode to electroplate iron substances with copper?

1. Iron substance
2. Copperplate
3. Carbon substance
4. Nickel substance

Answer: 1. Iron substance

Question 10. Which of the following is used as cathode to electroplate on a substance with gold (gold plating)?

1. Pure gold plate
2. The substance on which gold plating is to be done
3. Platinum plate
4. Copperplate

Answer: 2. The substance on which gold plating is to be done

Question 11. Which of the following is used as anode in the electrorefining of copper?

1. Copper
2. Graphite
3. Platinum
4. Steel

Answer: 1. Copper

Physical Science Class 10 West Bengal Board

Question 12. Which one of the following is used as anode to electroplate a spoon of silver by gold?

1. Pt
2. Ag
3. Au
4. Graphite

Answer: 3. Au

Question 13. Which of the following metal is obtained from anode mud?

1. Au
2. Mg
3. Al
4. Na

Answer: 1. Au

Question 14. Which of the following metal can not be extracted by electrolysis?

1. Na
2. Zn
3. Al
4. K

Answer: 2. Zn

Question 15. On which of the following metal can anodizing be done?

1. Iron
2. Aluminium
3. Copper
4. Zinc

Answer: 2. Aluminium

Question 16. Which of the following is used as anode to electroplate iron with nickel?

1. Iron
2. Nickel sulfate
3. Nickel
4. NiSO₄ + H₂SO₄

Answer: 3. Nickel

Electric Current And Chemical Reactions Topic B Application Of Electrolysis Answer In Brief

Question 1. Mention some important practical applications of electrolysis.
Answer:

Some of the important practical applications of electrolysi are:

1. Electroplating, electrorefining and
2. Metal extraction by electrolytic reduction.

Question 2. Which compounds are used as cathode and anode during the extraction of aluminium from bauxite?
Answer: Graphite as anode and gas carbon as cathode.

Question 3. Which substances are added to alumina during extraction of aluminium by electrolytic reduction?
Answer: Cryolite (AIF₃ • 3NaF) and fluorspar (CaF₂)

Physical Science Class 10 West Bengal Board

Question 4. Name a metal which is extracted by electrolytic process.
Answer: Aluminium.

Question 5. What is the melting point of the electrolytic mixture containing alumina, cryolite and fluorspar?
Answer: 900°C.

Wbbse Class 10 Current Electricity Questions And Answers

Question 6. Name a metal other than aluminium which is extracted by electrolytic reduction.
Answer: Sodium.

Question 7. How many electrons are exchanged between the cathode and anode during aluminium extraction?
Answer: 6 electrons are exchanged between the cathode and anode during aluminium extraction.

Cathode:\(2 \mathrm{Al}^{3+}+6 e \rightarrow 2 \mathrm{Al}\)

Anode: \(3O^{2-} \rightarrow 3O+6 e\)

Question 8. What are the products obtained during aluminium extraction form alumina?
Answer: Aluminium metal is obtained at cathode and oxygen gas is obtained at anode.

Question 9. State the composition of the electrolytic mixture used in the extraction of aluminium by electrolytic method.
Answer: 20% alumina (AI₂O₃),60% cryolite (Na₃AIF₆) and 20% fluorspar (CaF₂).

Question 10. Name the electrolyte used during electroplating of a metallic object by gold?
Answer: Potassium aurocyanide, K[Au(CN)₂].

Physical Science Class 10 West Bengal Board

Question 11. As which electrode the impure copper rod is taken during the purification of copper in electrolytic method?
Answer: A thick slab of impure copper is taken as an anode.

Question 12. Name an element present in anode mud.
Answer: Gold (Au).

Question 13. What should be used as the electrolyte to electroplate an iron spoon with chromium?
Answer: A mixture of chromic sulphate solution and a little amount of chromic acid i.e., Cr₂(SO₄)₃ + H₂CrO₄.

Question 14. Name the electrolyte used during electroplating of copper on any subject.
Answer: Aqueous copper sulphate solution along with a little amount of sulfuric acid.

Question 15. What substance do you take as electrolyte to electroplate a silver spoon with gold?
Answer: Potassium aurocyanide (K[Au(CN)₂]) .

Question 16. What should be the electrolyte for the electroplating of an iron spoon by nickel?
Answer: A mixture of nickel sulphate and a little amount of boric acid.

Question 17. What can be taken as cathode while electroplating a copper spoon with silver?
Answer: The copper spoon.

Electric Current And Chemical Reactions Topic B Application Of Electrolysis Fill In The Blanks

Question 1. During electroplating, metal plate with which the electroplating is to be done is taken as the ________
Answer: Anode

Question 2. During electroplating, the object on which the plating is to be done is taken as the ________
Answer: Cathode

Question 3. During electroplating, a _______ electric current should be passed through the solution for ______ period of time.
Answer: Small,long

Question 4. Highly _________ renderer metals are extracted from their ores by electrolytic reduction method.
Answer: Electropositive

Question 5. Almost ________ pure copper is obtained by electrorefining.
Answer: 99.9%

Physical Science Class 10 West Bengal Board

Question 6. To reduce the melting point of the electrolyte in aluminium extraction _______ are mixed with alumina.
Answer: Cryolite,fluorspar

Question 7. The electrolyte used in Al-extraction melts at ______
Answer: 900C

Question 8. ______ metal can be purified by electrolytic method.
Answer: Copper

Question 9. By electroplating coating of ______ metal is done on ______ reactive metal.
Answer: Less, more

Question 10. During silver plating rod of pure _______ is used as anode.
Answer: Silver

Electric Current And Chemical Reactions Topic B Application Of Electrolysis State Whether True Or false

Question 1. During extraction of aluminium from bauxite, graphite is used as anode and gas carbon is used as cathode.
Answer: True

Question 2. During electroplating of an object by nickel, the electrolyte used is NiCI₂ solution.
Answer: False

Question 3. In case of electrorefining, a rod of impure metal is taken as anode while a rod of pure metal is taken as cathode.
Answer: True

Question 4. Less reactive metals are generally extracted from their ores by electrolytic reduction.
Answer: False

Question 5. Ag, Au, Pt etc, metals can be found in anode mud.
Answer: True

Question 6. Coating of more reactive metal is done on less reactive metal by electroplating.
Answer: False

Question 7. The substance on which electroplating is to be done is used as cathode.
Answer: True

Physical Science Class 10 West Bengal Board

Question 8. Gold plate is used as cathode electroplating silver jewellery by gold.
Answer: False

Electric Current And Chemical Reactions Miscellaneous Type Questions Match The Columns

Question 1.

Column A	Column B
Liquid non-conductor	1. Hg
Solid conductor	2. Sulphur
Solid non-conductor	3. Br2
Liquid conductor	4. Graphite

 

Answer:
Liquid non-conductor: 3. Br₂
Solid conductor: 4. Graphite
Solid non-conductor:  2. Sulphur
Liquid conductor:  1. Hg

Question 2.

Column A	Column B
Non-metallic electrode	1. Pure water
Anode	2. K[Ag(CN)2]
Electroplating by gold	3. Graphite
Non-conductor	4. Oxidation occurs

 

Answer:
Non-metallic electrode: 2. K[Ag(CN)₂]
Anode: 4. Oxidation occurs
Electroplating by gold: 1. Pure water
Non-conductor: 3. Graphite

WBBSE Solutions for Class 10 Physical Science and Environment