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Some GasesSolved Questions· Unit 16
Science & Technology · Chapter 16
30 solved questions

Chapter 16: Gases

Every question in this chapter, answered and explained — step-by-step solutions drawn live from the chapter library across 7 question sections.

Very Short Answer Questions8Short Answer Questions6Give Reason Questions4Differentiate Between1Numerical / Reaction-Based Problems5Application / Conceptual Questions3Additional SEE Practice3
01

Very Short Answer Questions

8
1SEE Boardqb-q0

Write the chemical formula and molecular weight of carbon dioxide.

Ans.Chemical formula: CO2; Molecular weight: 44.
2SEE Boardqb-q1

Write the chemical formula and molecular weight of ammonia.

Ans.Chemical formula: NH3; Molecular weight: 17.
3SEE Boardqb-q2

Who discovered carbon dioxide, and when?

Ans.Van Helmont discovered carbon dioxide in 1630 AD by burning wood.
4SEE Boardqb-q3

Name the substance formed when CO2 is cooled below -78°C.

Ans.It forms a solid called dry ice.
5SEE Boardqb-q4

Why is carbon dioxide collected by upward displacement of air?

Ans.Because carbon dioxide is heavier than air, it sinks and is collected by upward displacement of air.
6SEE Boardqb-q5

Why is ammonia collected by downward displacement of air?

Ans.Because ammonia is lighter than air, it rises and is collected by downward displacement of air.
7SEE Boardqb-q6

What is carbogen and what is it used for?

Ans.Carbogen is a mixture of 95% oxygen and 5% carbon dioxide, used for artificial respiration in patients suffering from pneumonia.
8SEE Boardqb-q7

What is the ratio of ammonium chloride to calcium hydroxide used in the laboratory preparation of ammonia?

Ans.2:1 (ammonium chloride : calcium hydroxide).
02

Short Answer Questions

6
1SEE Boardqb-q8

Write any three physical properties of carbon dioxide gas.

Ans.
  1. (i) It is colourless and odourless.
  2. (ii) It is 1.5 times heavier than air.
  3. (iii) It turns moist blue litmus paper red and is slightly soluble in water, forming carbonic acid.
2SEE Boardqb-q9

Write any four uses of carbon dioxide gas.

Ans.
  1. (i) Used in soft drinks.
  2. (ii) Used by plants for photosynthesis.
  3. (iii) Used in fire extinguishers.
  4. (iv) Used to make dry ice for preserving food.
3SEE Boardqb-q10

Write any four uses of ammonia gas.

Ans.
  1. (i) Used to make fertilizers like ammonium sulphate and urea.
  2. (ii) Used to manufacture nitric acid.
  3. (iii) Used as a refrigerant/cooling agent.
  4. (iv) Used as a cleansing agent to remove oil and grease stains.
4SEE Boardqb-q11

What is the lime tower used for in the preparation of ammonia gas?

Ans.The lime tower is filled with calcium oxide (CaO), which absorbs moisture from the ammonia gas passing through it, giving pure and dry ammonia gas.
5SEE Boardqb-q12

What is the greenhouse effect?

Ans.The process of trapping solar energy inside a greenhouse (or the Earth's atmosphere by greenhouse gases), which increases the temperature inside it, is called the greenhouse effect.
6SEE Boardqb-q13

What is acid rain?

Ans.Rain water that becomes more acidic (pH about 3 to 5) because gases like sulphur dioxide, carbon dioxide, and nitrous oxide dissolve in atmospheric water vapour to form acids, which then fall with rain, is called acid rain.
03

Give Reason Questions

4
1SEE Boardqb-q14

Carbon dioxide can be collected in an open glass jar.

Ans.Carbon dioxide can be collected in an open glass jar because it is heavier than air and neither reacts with air nor escapes upward easily; it simply settles and fills the jar by upward displacement of air.
2SEE Boardqb-q15

The bottle of liquid ammonia should be placed in cold water or ice for some time before opening its lid.

Ans.Liquid ammonia is under high pressure inside the bottle. Cooling it in cold water or ice reduces this pressure, preventing the ammonia solution from spilling out suddenly when the lid is opened.
3SEE Boardqb-q16

The end of the delivery tube should not be dipped into the acid while preparing carbon dioxide.

Ans.If the delivery tube's end is dipped into the acid, the acid or the gas pressure could push liquid back up the tube and block the flow of gas, so the delivery tube must stay above the acid level while the thistle funnel's end must remain dipped in the acid to keep the system airtight.
4SEE Boardqb-q17

Ammonia gas is not collected by the displacement of water.

Ans.Ammonia gas is highly soluble in water, so if collected by downward displacement (or upward displacement) of water, most of the gas would simply dissolve into the water instead of collecting in the jar. Therefore it is collected by downward displacement of air.
04

Differentiate Between

1
1SEE Boardqb-q18

Carbon Dioxide Gas and Ammonia Gas

Carbon Dioxide (CO2)Ammonia (NH3)
Acidic gas; turns moist blue litmus red.Basic gas; turns moist red litmus blue.
Heavier than air; collected by upward displacement of air.Lighter than air; collected by downward displacement of air.
Prepared from limestone and dilute HCl.Prepared from ammonium chloride and calcium hydroxide.
05

Numerical / Reaction-Based Problems

5
1SEE Boardqb-q19

Write the balanced chemical equation for the laboratory preparation of carbon dioxide gas.

Ans.CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g).
2SEE Boardqb-q20

Write the balanced chemical equation for the laboratory preparation of ammonia gas.

Ans.2NH4Cl(s) + Ca(OH)2(s) → CaCl2(s) + 2H2O(l) + 2NH3(g).
3SEE Boardqb-q21

Write the balanced chemical equation of the reaction inside a fire extinguisher.

Ans.2NaHCO3 + H2SO4 → Na2SO4 + 2H2O + 2CO2.
4SEE Boardqb-q22

Write the balanced chemical equation for the formation of urea from ammonia and carbon dioxide.

Ans.NH3(g) + CO2(g) --1500°C, pressure--> NH2-CO-NH2(s) + H2O(l).
5SEE Boardqb-q23

Write the balanced chemical equations showing how limewater first turns milky and then becomes colourless with excess carbon dioxide.

Ans.Ca(OH)2(aq) + CO2(g) → CaCO3(s) [milky] + H2O(l); on passing excess CO2: CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq) [colourless].
06

Application / Conceptual Questions

3
1SEE Boardqb-q24

What happens when carbon dioxide is passed through lime water for some time, and then for a long time? Explain with balanced chemical reactions.

Ans.When passed for some time, carbon dioxide reacts with calcium hydroxide (lime water) to form insoluble calcium carbonate, which turns the lime water milky white: Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l). When carbon dioxide is passed for a long time, the calcium carbonate further reacts to form soluble calcium bicarbonate, and the milky white colour disappears: CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq).
2SEE Boardqb-q25

What happens when a burning magnesium ribbon is inserted into a jar full of carbon dioxide gas? Write the balanced chemical reaction.

Ans.The burning magnesium continues to burn brightly inside the carbon dioxide, because magnesium is reactive enough to take oxygen from CO2. It forms white magnesium oxide powder and black carbon powder, proving that CO2 contains carbon: 2Mg(s) + CO2(g) → 2MgO(s) + C(s).
3SEE Boardqb-q26

What happens when ammonia gas is mixed with water? What happens when ammonia reacts with hydrochloric acid?

Ans.When mixed with water, ammonia dissolves to form ammonium hydroxide, a base: NH3(g) + H2O(l) → NH4OH(aq). When ammonia reacts with hydrochloric acid, it forms ammonium chloride, seen as dense white fumes: NH3(g) + HCl(aq) → NH4Cl(aq).
07

Additional SEE Practice

3
1SEE Boardqb-q27

Why does a burning matchstick get extinguished when brought near the mouth of a gas jar containing carbon dioxide?

Ans.Carbon dioxide is neither combustible nor a supporter of combustion, so it cuts off the oxygen supply needed for burning, extinguishing the matchstick.
2SEE Boardqb-q28

State two effects of the greenhouse effect on the environment.

Ans.Any two: increase in global temperature; melting of Himalayan snow and glaciers; rising sea levels causing coastal flooding; decrease in agricultural productivity; imbalance in ecosystems.
3SEE Boardqb-q29

Name two gases responsible for acid rain and the acids they form.

Ans.Sulphur dioxide (SO2) forms sulphuric acid (H2SO4); carbon dioxide (CO2) forms carbonic acid (H2CO3). (Nitrous oxides also form nitric acid, HNO3.)
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