Chapter 3 Some Common Gases Short Answer Type Questions
Question 1. Why the use of LED is advantageous for laboratory use over common bulbs?
Answer:
LED is advantageous over common bulbs because:
1. it has a long life;
2. during repeated use they do not get fused easily and they can glow even when a very small current is flowing through the electric circuit. So it can detect very small currents flowing through an electrical circuit.
Question 2. How oxygen was formed on earth?
Answer:
Oxygen was formed on earth:
The earth was created approximately 4500 million years ago. The atmosphere of the earth was composed of main hydrogen, ammonia, nitrogen, carbon dioxide, hydrogen sulphide and methane.
The abundance of oxygen was very very low. About 2500 million years ago, a type of bacteria, called cyanobacteria emerged in the sea.
With the help of sunlight and special protein, they started splitting water to form oxygen. As a result the amount of oxygen in the atmosphere gradually started to rise and approximately 500 million years ago, the amount of oxygen attained the present level.
Question 3. Why the presence of oxygen in the atmosphere is a must for us?
Answer:
The presence of oxygen in the atmosphere is a must for us:
The presence of oxygen in the atmosphere is a must for us. Because it is essential for respiration. Respiration is a process by which energy is liberated from intracellular glucose in a very efficient way.
Read And Learn More WBBSE Solutions For Class 8 School Science Short Answer Type Questions
This liberated 20 energy is used for various biochemical and biophysical processes continuously occurring in our body so that we can remain alive.
Question 4. Do all organisms on the earth require oxygen? No, not all organisms require oxygen for their survival. Answer: There are some areas in the earth where oxygen cannot penetrate.
Answer:
For example, in the depth of marshes or into the sludge of urban sewers, oxygen is totally absent. Some bacteria still live there, which are known as obligate anaerobes.
They produce energy within their bodies by using a different mechanism, which does not require the involvement of oxygen.
Question 5. Is the presence of oxygen always beneficial for us?
Answer:
Energy is liberated from glucose in presence of oxygen in a very efficient way within our bodies.
But, along with the generation of energy vital for maintaining all our biophysical and biochemical processes, it forms some harmful chemicals such as hydrogen peroxide (H2O2) and superoxide ions (O2).
They can cause great damage to cellular DNA even when they are present in small amounts.
Question 6. How hydrogen peroxide and superoxide ions formed in our body are removed?
Answer:
Hydrogen peroxide (H2O2) and superoxide ions (O2) are very harmful to our bodies.
They can cause great damage to cellular DNA even when they are present in small amounts. Certain enzymes present within the living cells of our body can destroy these species.
For example, the enzyme, catalase, can break down hydrogen peroxide into oxygen and water.
Question 7. Why manganese dioxide is used during the preparation of oxygen from potassium chlorate?
Answer:
During the preparation of oxygen from potassium chlorate, MnO2 acts as a positive catalyst. If KCIO3 is heated alone, oxygen is produced at a temperature higher than 610°C.
In presence , of little amount of \(\mathrm{MnO}_2, \mathrm{KClO}_3\) decomposes at about 250°C to produce oxygen.
⇒ \(2 \mathrm{KClO}_3+\left[\mathrm{MnO}_2\right] \stackrel{\text { heat }(\Delta)}{\longrightarrow} 2 \mathrm{KCl}+3 \mathrm{O}_2+\left[\mathrm{MnO}_2\right]\)
Question 8. “Oxygen is chemically very reactive”—Briefly explain.
Answer:
“Oxygen is chemically very reactive”:
Oxygen is chemically very reactive and forms compounds with practically all elements. except for inert gases (such as helium, neon, argon etc.).
It combines with most of the elements except halogens (i.e. fluorine, chlorine, bromine, iodine, etc.) and a few noble metals (such as gold, platinum, etc.).
The reactivity of oxygen increases at high temperatures and in presence of a suitable catalyst. The compound produced in this reaction is called oxide.
Question 9. Discuss briefly the use of oxygen for medical purposes.
Answer:
The use of oxygen for medical purposes:
Oxygen is frequently used for medical purposes. For example, if patients suffer from asthma, pneumonia, etc. then they are supplied oxygen artificially (via gas cylinders).
For patients who are rendered unconscious due to inhalation of poisonous gas, the inhalation of carbogen (which is a mixture of 95% oxygen and 5% COJ is prescribed. A mixture of oxygen and nitrous oxide is used for anaesthesia.
Question 10. Briefly discuss the importance of oxygen in respiration.
Answer:
The importance of oxygen in respiration:
Respiration is a process by which complex foodstuffs, such as glucose is oxidized in living organisms and heat energy is liberated.
Except for some lower animals and plants, most animals and plants consume the oxygen present in the air for the oxidation of complex foodstuffs. We inhale air and use the oxygen present in it for respiration.
As a result, carbonaceous food kinds of stuff are converted into CO2. For example, during respiration in our body, glucose is oxidized to CO2 and H20.
Energy is liberated during this process which is utilized in different physicochemical processes occurring in our bodies.
⇒ \(\mathrm{C}_6 \mathrm{H}_{12} \mathrm{O}_6+6 \mathrm{O}_2 \rightarrow 6 \mathrm{CO}_2+6 \mathrm{H}_2 \mathrm{O}+\text { heat energy }\)
Question 11. When a balloon filled with hydrogen gas is released, it moves upwards—Why?
Answer:
When a balloon filled with hydrogen gas is released, it moves upwards:
Hydrogen is the lightest gas and air is nearly 14.4 times heavier than hydrogen. When a balloon filled with hydrogen gas is released, it goes up and touches the roof of the room where this experiment is being carried out.
This happens because the balloon filled up with hydrogen gas is lighter than the air displaced by it.
Question 12. Discuss briefly the “adsorption” of hydrogen.
Answer:
“Adsorption” of hydrogen:
Some metals like palladium, platinum, iron, nickel, etc. can adsorb hydrogen at normal temperatures. Palladium adsorbs the largest volume of hydrogen at 0°C.
This is known as occlusion. In this case, hydrogen is attached to the surface of these metals and is called adsorbed hydrogen.
When heated, the adsorbed hydrogen is released. Experimentally it has been found that adsorbed hydrogen is more, reactive than normal hydrogen.
Question 13. Why pure zinc is not used in the preparation of hydrogen gas?
Answer:
This is because pure zinc reacts very slowly with dilute sulphuric acid or dilute hydrochloric acid. Thus the production of hydrogen gas will be extremely small in quantity.
[In fact, the reaction of zinc with dilute acids (such as HCI or H2SO4) is an electrochemical process. The impurities like iron, lead, etc.
which are commonly present in commercial zinc forms tiny, local electrochemical cells. The impurities act as the positive pole of a tiny electrochemical cell and zinc acts as a negative pole and the dilute acid acts as the electrolyte.
Due to the formation of so many tiny, local, electrochemical cells, the rate of production of hydrogen increases
Question 14. Why concentrated H2S04 is not used in the preparation of hydrogen gas?
Answer:
This is because the acid produces sulphur dioxide gas during the reaction with zinc.
Also, when the acid is decomposed, it produces atomic oxygen (or nascent oxygen) \(\left[\mathrm{H}_2 \mathrm{SO}_4 \rightarrow \mathrm{H}_2 \mathrm{O}+\mathrm{SO}_2+\mathrm{O}\right]\) which combines with hydrogen (produced in the process) to form water.
Question 15. Why concentrated hydrochloric acid is not used in the preparation of hydrogen gas?
Answer:
This is because concentrated HCI is highly volatile and hence plenty of HCI vapour mixes with the hydrogen gas produced during the process.
Moreover, zinc reacting with HCI produces insoluble ZnCI2 which forms a coating on the metallic zinc and thus stops the further reaction.
Question 16. Why strong or moderately strong nitric acid is not used in the preparation of hydrogen gas?
Answer:
The acid decomposes even at room temperature to produce oxygen [4HNO3→4NO2 + 2H2O+ O2. This oxygen will thus combine with the hydrogen gas produced in the process to form water.
Question 17. Show that occluded hydrogen is a more powerful reducing agent than ordinary hydrogen.
Answer:
Ferric chloride is not reduced when hydrogen is bubbled through an aqueous solution (yellow-coloured) of the salt.
But, if a small quantity of spongy palladium, containing occluded hydrogen, is dipped into a solution of ferric chloride and heated,
it is immediately reduced to ferrous chloride as is shown by the change of the yellow colour of the solution into almost colourless (or light green).
FeCl3+H2(molecularhydrogen)→NoreactionFeCl3+[H](occludedhydrogen)→FeCl2+HCl.(yellow)(Colurless)