Carbon. Class 8 chemistry. Long Q&A

10. Question: Carbon dioxide occurs both in the free state and in the combined state. State three methods how carbon dioxide is added to the atmosphere.

Answer: Three methods are:

- Through respiration by living organisms

- Combustion of fossil fuels

- Volcanic eruptions and natural decomposition of organic matter

11. Question: In the laboratory preparation of carbon dioxide by action of a dilute acid on a metallic carbonate give:

a) A balanced equation for the preparation 

b) A reason for i) use of a wash bottle containing conc. H2SO4 ii) Not collecting the prepared gas over water iii) Not using dilute sulphuric acid as a reactant in the preparation.

Answer:

a) CaCO3 + 2HCl → CaCl2 + H2O + CO2

b) Reasons:

i) Wash bottle with conc. H2SO4: To dry the gas

ii) Not collected over water because CO2 is slightly soluble in water

iii) Dilute H2SO4 isn't used because CaSO4 formed is insoluble and coats unreacted carbonate

12. Question: How would you prove experimentally that a) Carbon dioxide does not support combustion b) Is slightly acidic in nature.

Answer:

a) Insert a burning splint into a jar of CO2 - it will extinguish

b) Bubble CO2 through water with universal indicator - color changes to slightly pink/red

13. Question: Starting from carbon dioxide how would you obtain a) A weak acid b) A fertilizer c) A highly poisonous gas d) Black particles of carbon. [Give balanced equations for the same]

Answer:

a) CO2 + H2O → H2CO3 (carbonic acid)

b) CO2 + 2NH3 + H2O → NH4HCO3 (ammonium bicarbonate)

c) CO2 + C → 2CO

d) CO2 + 2Mg → 2MgO + C

14. Question: State how you would convert carbon dioxide to a metallic carbonate using a basic oxide e.g. sodium oxide. [Give a balanced equation]

Answer: CO2 + Na2O → Na2CO3

15. Question: 'When carbon dioxide is bubbled into lime water, the lime water turns milky and when bubbled in excess the milkiness disappears'. Give balanced equations to support the statement.

Answer:

First reaction: Ca(OH)2 + CO2 → CaCO3↓ + H2O

Excess CO2: CaCO3 + H2O + CO2 → Ca(HCO3)2 (soluble)

16. Question: Explain the term 'dry ice'. State its application. Give three reasons why carbon dioxide finds application in fire extinguishers.

Answer:

- Dry ice is solid form of CO2

- Applications: Refrigeration, creating special effects (fog)

- Reasons for use in fire extinguishers:

1. Heavier than air, forms blanket over fire

2. Doesn't support combustion

3. Cooling effect when expanding

17. Question: Using a magnesium ribbon, how would you prove that a given gas jar contains carbon dioxide.

Answer: Burn Mg in the gas jar - if white ash (MgO) and black carbon particles form, it confirms CO2:

2Mg + CO2 → 2MgO + C

18. Question: State the function of conc. sulphuric acid in the laboratory preparation of carbon monoxide from oxalic acid.

Answer: It acts as a dehydrating agent, removing water from oxalic acid.

19. Question: Give reasons why carbon monoxide is considered a highly poisonous gas. State why it is dangerous i) To sleep in a closed room with a fuel burning ii) To be in the vicinity of smokers.

Answer: It's dangerous because it:

- Combines with hemoglobin forming stable carboxyhemoglobin

- Prevents oxygen transport in blood

- Is dangerous in closed rooms/near smokers as it's colorless, odorless, and highly toxic

20. Question: Convert carbon monoxide to carbon dioxide using two different methods.

Answer:

Method 1: 2CO + O2 → 2CO2

Method 2: CO + H2O → CO2 + H2 (water gas shift reaction)

21. Question: State how carbon monoxide finds application in i) The metallurgy of iron ii) Preparation of an alcohol. [Give balanced equations for the same]

Answer:

i) Metallurgy: CO acts as reducing agent

CO + Fe2O3 → 2Fe + 3CO2

ii) Alcohol preparation:

CO + 2H2 → CH3OH (methanol)