Ans: Hydrogen is called the simplest element because it is composed of a proton and an electron.
2. What is hydrogen?
Ans: Hydrogen is the lightest gaseous element situated on first period and group IA of the periodic table.
3. How hydrogen is manufactured in the industry?
Ans: Hydrogen is manufactured in industry by the reaction of hydrocarbon with water vapour.
4. What is a catalyst?
Ans: A catalyst is a chemical substance which increases or decreases the rate of chemical reaction but never participates in the reaction.
5. What happens when magnesium is burnt?
Ans: When magnesium is burnt, magnesium metal reacts with oxygen present in air and magnesium oxide is formed.
6. Why is nitrogen gas filled in electric bulbs?
Ans: Nitrogen gas is filled in electric bulb because it does not react with oxygen and prevents burning.
7. What is nascent hydroge?
Ans: The hydrogen atom at the moment of birth which is highly reactive is called nascent hydrogen.
8. What is hydrogenation?
Ans: Hydrogenation is the process by which vegetable oil is changed into vanaspati ghee.
9. What are the methods applied for extracting hydrogen from water?
Ans: Hydrogen gas is extracted by the electrolysis of water and by the action of certain metals on water.
10. In which electrode is hydrogen gas collected ?
Ans: Hydrogen gas is collected in the cathode during the electrolysis of water.
11. Why is nickel used in the manufacture of hydrogen gas?
Ans: Nickel is used in the manufacture of hydrogen gas because it acts as a positive catalyst which increases the rate of production of hydrogen gas.
12. What happens when hydrogen is passed through a red hot copper oxide?
Ans: When hydrogen gas is passed through a red hot copper oxide, copper oxide is reduced to copper and water is produced.
13. What should be done to extract lead oxide?
Ans: Hydrogen gas should be passed through the heated lead oxide to extract lead.
14. Why do we use manganese dioxide while preparing oxygen gas?
Ans: Manganese dioxide is used while preparing oxygen gas because it is acts as a positive catalyst which helps in early releasing of oxygen from potassium chlorate at lower temperature.
15. State the principle of laboratory preparation of hydrogen gas.
Ans: Hydrogen gas can be prepared in laboratory by the action of dilute hydrochloric acid or sulphuric acid on zinc metal.
16. What is the position of oxygen in the periodic table?
Ans: Oxygen is situated in second period and group VIA of the periodic table.
17. How do aquatic animals get oxygen?
Ans: Aquatic animals absorb the dissolved oxygen in water for breathing.
18. Why is oxygen collected by downward displacement of water?
Ans: Oxygen is collected by downward displacement of water because it is slightly soluble in water and is less dense than water.
19. How do you understand by Haber’s process?
Ans: The process of manufacture of ammonia by the reaction of nitrogen and hydrogen in the ratio 1: 3 at 500°C temperature and 200 atm. pressure in the presence of iron catalyst and molybdenum promoter is known as Haber’s process.
20. Hydrogen is generally not found in air in free state. Why?
Ans: Since hydrogen is more reactive gas; it reacts with other elements very easily, so it is generally not found in free state.
21. Why granulated zinc is used instead of pure zinc during lab preparation of hydrogen gas?
Ans: It is because pure zinc reacts slowly with dilute sulphuric acid but granulated zinc reacts fast.
22. Why nitrogen gas is used for replacing fuels in tanks of aeroplanes?
Ans: It is because nitrogen gas being inactive gas prevents the formation of explosive mixture of fuel and air.
23. Why nitrogen gas is called an inactive gas?
Ans: Nitrogen gas is called an inactive gas because it is chemically inert gas and does not take part in chemical reaction.
24. Who discovered hydrogen gas ?
Ans: A British scientist, Henry Cavendish discovered Hydrogen gas in 1776.
25. Write any 4 physical properties of hydrogen.
Ans: The physical properties of hydrogen are as follows:
• It is colorless, odourlees and tasteless gas.
• It is lighter than air.
• It is slightly soluble in water.
• Its melting point is -259°C and boiling point is -253 °C.
26. What is the melting point of hydrogen ?
Ans: The melting point of hydrogen is -259°C.
27. Why is hydrogen gas collected by downward displacement of water ?
Ans: Hydrogen gas is collected by the downward displacement of water because it is lighter than the air.
28. What is water gas ?
Ans: The mixture of carbon monoxide and hydrogen gas is called water gas. It is used in industry as a source of heat.
29. Why is hydrogen gas not found in air ?
Ans: Hydrogen gas is not found in air because it is lighter than air and is very reactive so it takes part in chemical reaction to give rise to the different compounds.
30. Give any four precautions which we should follow during the laboratory preparation of hydrogen gas ?
Ans: Precautions which we should follow during the laboratory preparation of Hydrogen gas are as follows:
• Concentrated acid should not be used.
• Impure zinc should be used so that reaction occurs at fast rate.
• The apparatus should be made air tight.
• The end of funnel should be dipped inside the acid in thistle but the delivery tube should not be dipped as gases may escape out.
31. How do you test hydrogen gas ?
Ans: Hydrogen gas is highly combustible gas but not supporter of combustion. When a burning matchstick is brought near a test tube full of hydrogen gas then the fire goes out producing 'pop' sound and hydrogen gas gets burned with a blue flame. Thus, we can say that hydrogen gas does not help other substances to burn.
32. What is nascent hydrogen ?
Ans: The atomic form of hydrogen produced at the time of chemical reaction is known as nascent hydrogen. Nascent means newly born.
33. How is hydrogen manufactured from methane ?
Ans: In the industrial sector, hydrogen is produced by the reaction between hydrocarbon and water vapor.
For industrial purpose, hydrogen gas is prepared by reacting methane with water vapour at very high temperature in the presence of nickel powder, which acts as catalyst in a reaction.
CH₄ + H₂O
34. Define hydrogenation.
Ans: Under suitable conditions of temperature and pressure, unsaturated hydrocarbons directly combine with hydrogen gas to form saturated hydrocarbons. This process is known as hydrogenation.
35. What do you mean by a reduction reaction and a reducing agent ?
Ans: When dry hydrogen is passed over the heated oxides of metal like iron, copper and lead, metal gets separated and water is formed. So the removal of oxygen from their metal oxides is called reduction reaction and the hydrogen which brings the reduction is reducing agent.
36. What happens when:-
a) Hydrogen is passed over hot ferric oxide.
b) Hydrogen combines with chlorine.
c) Iron reacts with hydrochloric acid.
d) Hydrogen burns with oxygen.
Ans: a. Fe2O3 + 3H2 → 2Fe
b. H2 + Cl2 → 2HCl
c. Fe + 2HCl → FeCl2 + H2
d. When hydrogen is mixed in air, it burns with a pop sound and forms water. But pure hydrogen gas burns with light flame when mixed with oxygen to form water. 2H2 + O2 → 2H2O
37. Generally hydrogen is not found in the air in free state. Why ?
Ans: Hydrogen is more reactive gas. Therefore, it reacts with other elements moreover, it is the lightest gas. Therefore, it is generally not found in atmosphere.
38. Impure granulated zinc is used instead of pure zinc during lab preparation of hydrogen gas, why ?
Ans: Pure zinc reacts with dilute sulphuric acid slowly but the granulated zinc reacts with dilute sulphuric acid fast. Therefore, granulated zinc is used instead of pure zinc during lab preparation of hydrogen gas.
39. Many metals displace the hydrogen from the acids, why ?
Ans: It is because metal are more reactive or more electropositive than hydrogen.
40. Oxides of zinc, calcium and magnesium are not reduced by hydrogen, why ?
Ans: It is because the metals mentioned above are more reactive than hydrogen.
41. Zinc is mostly used for the laboratory preparation of hydrogen gas rather than others metals, why ?
Ans: It is because of the following facts:
• Metals like sodium and potassium reacts violently with acid.
• Calcium and magnesium are very expensive in comparison to zinc.
• Aluminium forms a protective coating of Al₂0₃ whereas iron reacts with acid very slowly and requires more heat.
42. What is the role of manganese dioxide in the preparation of oxygen gas in the laboratory ?
Ans: Manganese dioxide is used in a preparation of oxygen gas as a positive catalyst which accelerates the rate of chemical reaction.
43. What happens when the potassium permanganate is heated ?
Ans: When the potassium permanganate is heated, it gives rise to the manganese oxide and oxygen gas. The reaction occurs as follows:
2KMnO4
44. Enlist the physical properties of oxygen gas?
Ans: Physical properties of oxygen gas:
• It is a neutral gas doesn’t have any effect on the indicators.
• It is colorless odorless and tasteless gas.
• It is heavier than air.
• It is slightly soluble in water.
45. What is the position of oxygen in periodic table ?
Ans: Oxygen is the first member of the group VIA on the periodic table. It is located in period 2 and group 16.
46. What are the uses of oxygen ?
Ans: We used oxygen for respiration as fuel and welding and cutting of metals also.
47. What are the physical properties of oxygen ?
Ans: The physical properties of oxygen are:
• Oxygen is colorless, odourless and tasteless gas.
• It is slightly soluble in water.
• It is neutral to indicator.
48. How will you prepare oxygen gas in the laboratory ?
Ans: In a laboratory oxygen gas is prepare by heating the potassium chlorate and manganese dioxide acts as a catalyst.
49. What happens when burning charcoal is kept in gas jar containing oxygen ?
Ans: When burning charcoal is kept in the jar containing oxygen gas carbon dioxide is formed.
C + O2
50. What is rusting of iron ?
Ans: The process of forming rust when iron reacts with oxygen in the presence of moisture.
4Fe + 3O2 + xH2O → 2Fe2O3..xH2O
51. What do you mean by oxy-acetylene flame ?
Ans: The flame made by burning oxygen and acetylene and used for cutting and welding metals is called oxy-acetylene flame.
52. Some amount of oxygen is dissolved in water, why ?
Ans: It is because the solution of oxygen in water provides the source of oxygen for respiration for the aquatic animals.
53. What happens when an alkaline pyrogallol solution is added to an oxygen containing jar ?
Ans: When the alkaline pyrogallol solution is added to an oxygen containing jar, the oxygen gets dissolved in it giving rise to the dark brown color to the solution.
54. How can we prepare oxygen gas in laboratory without heat ?
Ans: Oxygen is prepared in the laboratory by the decomposition of hydrogen peroxide (H2O2) into water and oxygen in the presence of Manganese dioxide (MnO2) as catalyst.
55. What are the uses of oxygen ?
Ans: The three uses of oxygen are as follows:
• Living organisms use oxygen during respiration.
• Liquid oxygen is used as fuel in missile and rocket.
• Mountaineers carry oxygen cylinders and masks with them so that they can breathe easily at high altitude
56. What happens when the following elements and compounds burn in oxygen ? Write the chemical reaction.
a) Calcium
b) Phosphorus
c) Magnesium
d) Glucose
Ans: a. Calcium oxide is formed.
2Ca + O2
b. Phosphorous pentoxide is formed
4P + 5O2 → 2P2O5
c. When magnesium is burnt in air then magnesium oxide is formed. Magnesium reacts with air and forms magnesium oxide which is an alkali.
2Mg + O2 → 2MgO
d. Energy is released.
C₆H12O6 + 6O2 → 6CO2 + 6H2O + energy
57. What is the position of nitrogen in periodic table ?
Ans: Nitrogen has 5 electrons in its valence shell and it belongs to the VA group of periodic table. As there are two shells, it belongs to the 2nd period of the periodic table. It is non – metal.
58. How will you prepare nitrogen gas in industrial scale ?
Ans: In the industrial sector, ammonia is manufactured at the Haber's synthesis process. In this process, nitrogen and hydrogen are heated in the ratio of 1:3 in the presence of iron as catalyst and molybdenum as promoter at temperature of about 500°C, under high pressure of about 200 - 900 atmospheric pressure.
N2 + 3H2
59. What are the physical properties of nitrogen ?
Ans: Physical properties of nitrogen are as follows:
• It is colorless, odorless and tasteless.
• It is slightly lighter than air.
• It is not soluble in water.
60. What happens when a burning magnesium ribbon is inserted in a jar containing nitrogen gas ? Also write the chemical equation.
Ans: When the magnesium ribbon is inserted in the jar containing the nitrogen gas, it burns and produce the yellowish white color called magnesium nitride.
3Mg + N2
61. What is chemical nitrogen ?
Ans: The nitrogen obtained from the nitrogenous compound in its pure form is called chemical nitrogen.
62. What happens when nitrogen combines with oxygen at a high temperature ?
Ans: At very high temperature, nitrogen and oxygen combines with to form a nitric oxide.
N2 + O2
63. Describe the preparation of nitrogen by heating copper method in short.
Ans: At first, air is passed through lime water and then to conc. Sulphuric acid to make air free from carbon dioxide gas .Now the air contains nitrogen and oxygen which is passed over heated copper. As the nitrogen escapes away, oxygen reacts with copper to produce copper oxide.
2Cu + O2
64. What is nitrogen ?
Ans: Nitrogen is an inert gas which constitutes about 78% by the volume of the atmosphere.
65. What are the three uses of nitrogen ?
Ans: We use nitrogen gas for:
• Manufacturing nitric acid.
• Manufacturing of nitrogen rich fertilizer.
• Nitrogen gas is used to manufacture explosive.
66. Nitrogen gas is an inactive gas, why ?
Ans: Molecules of nitrogen gas are formed by the combination of two atoms of Nitrogen. These two atoms are held together by a very strong triple bond. Since huge amount of energy is required to break this bond, nitrogen does not take part in chemical reaction. Thus the nitrogen is an inactive gas.
67. Nitrogen gas is used for replacing fuels in fuel tank of aeroplanes, why ?
Ans: Nitrogen gas being inactive gas prevents the formation of explosive mixture of fuel and air. Therefore, it is used for replacing fuels in fuels tanks of aeroplanes.
68. What is Haber’s process ? Write with balanced chemical equation.
Ans: When a mixture of hydrogen and nitrogen in the ratio of 3:1 by volume is heated to about 450°C under the pressure of 200 - 600 atmosphere in the presence of finely divided iron as catalyst and Molybdenum (Mo) as promoter, ammonia gas is produced. This process is known as Haber’s process.
69. What is biocatalyst ?
Ans: Biocatalyst is the biochemical compound like enzyme that helps to increase or decrease the rate of chemical reaction.
70. What are isotopes ?
Ans: Isotopes are the elements having the same atomic number but different atomic masses.
71. What is combustion ?
Ans: Combustion is the process of burning hydrogen with oxygen to produce water.
72. Answer the following question after observing the figure .
a) Which gas is going to be prepared in the figure?
b) What are the mistakes in the arrangement? Correct the figure.
c) Write the formula equation for the preparation of the gas?
d) What happens when a burning match stick is held near the gas jar?
e) Give any three uses of the gas?
f) What happens when concentrated sulphuric acid is used instead of dilute sulphuric acid in it?
b. The end of thistle funnel must be under the acid in Woulfe’s bottle and delivery tube should not be dipped under the acid in Woulfe’s bottle.
c. Granulated Zn + H2SO4 → ZnSO4 + H2
d. When a burning matchstick is brought near a test tube full of hydrogen gas then the fire goes out producing pop sound forming blue flume.
e. The main uses of hydrogen are as follows:
• It is used as a reducing agent in industries and laboratory.
• It is used to fill in the balloons as it is the lightest gas but it is mixed with helium as hydrogen is highly inflammable.
• It is used to prepare chemical fertilizers.
f. If conc. sulphuric acid is used instead of dilute sulphuric acid, suphur dioxide is produced instead of hydrogen gas.
Zn + conc.H2SO4 → ZnO + H2O + SO2
Instead when the dilute H2SO4 is used, the following reaction occurs to form the hydrogen gas.
Zn + dil. H2SO4 → ZnSO4 + H2
73. How is hydrogen manufactured from electrolysis of water ?
Ans: The process of the decomposition of the water into oxygen and hydrogen gas when the electric current is passed through the water is called Electrolysis of water.
Fig: Electrolysis of water
When dil. H2SO4 is mixed with water
H2O(HOH) → H+ + OH-
At anode
OH- - → OH + e-
4OH → 2H2O + O2
At cathode
H+ + e- → H
4H → 2H2
Overall reaction is
2H2O → 2H2 + O2
Hence, hydrogen is formed at cathode and oxygen is formed at anode.
74. How is oxygen gas is prepared in laboratory by the actions of heat ? Draw a necessary labeled diagram and mention the chemical equation.
Ans: Laboratory preparation of oxygen gas:
For the manufacture of oxygen gas in the laboratory (by heating), potassium chlorate or potassium permanganate is heated in a herd test tube vigorously.
Small amount of potassium permanganate or potassium chlorate is taken in a hard test tube and heated vigorously. A burning matchstick is taken to the test tube and observed. We can see that at very high temperature of (360 – 370)oC oxygen is evolved. This is high temperature to maintain so manganese dioxide is taken on a different test tube along with potassium chlorate and is heated. Manganese dioxide acts as catalyst and this helps in formation of oxygen at (240-250)oC. The oxygen produced is collected in the gas jar by downward displacement of water.
KClO3 → 2KCl + 3O2
Fig. Arrangement of apparatus for the preparation of oxygen
75. Which chemical is used for reacting with NH4Cl to produce nitrogen gas in the laboratory ? Draw a neat and labeled diagram for the preparation of nitrogen gas in the laboratory. Mention the chemical equation.
Ans: Nitrogen gas is prepared in the laboratory by the mixture of sodium nitrate and ammonium chloride is heated. This results in the production of nitrogen which is collected in the gas jar by the downward displacement of water.
NaNO2 + NH4Cl → NaCl + 2H2O + N2
76. Write the composition of air.
Ans: Air is composed of mainly nitrogen (78.06%) and oxygen (21.97%), which occupy about 99% by volume of air. Other minor constituents include water vapor, dust particles along with other inert gases like neon, argon etc.