Distinguish between a saturated and an unsaturated hydrocarbon by flame test. List the products of combustion reaction of a saturated hydrocarbon.

Q: Distinguish between a saturated and an unsaturated hydrocarbon by flame test. List the products of combustion reaction of a saturated hydrocarbon.

### Distinction by Flame Test 1. **Saturated Hydrocarbons:** When burnt in air, saturated hydrocarbons undergo complete combustion and burn with a **clean, blue, non-sooty flame**. 2. **Unsaturated Hydrocarbons:** When burnt in air, unsaturated hydrocarbons undergo incomplete combustion due to a higher percentage of carbon, burning with a **yellow, smoky, sooty flame**. ### Products of Combustion of a Saturated Hydrocarbon When a saturated hydrocarbon (such as methane, $\mathrm{CH_4}$) undergoes complete combustion in the presence of oxygen, the products formed are: - Carbon dioxide ($\mathrm{CO_2}$) - Water vapour ($\mathrm{H_2O}$) - Heat and light $$\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + Heat\ and\ Light}$$

Carbon and its Compounds

Saturated and Unsaturated Carbon Compounds

Official Answer

Distinction by Flame Test

Saturated Hydrocarbons: When burnt in air, saturated hydrocarbons undergo complete combustion and burn with a clean, blue, non-sooty flame.
Unsaturated Hydrocarbons: When burnt in air, unsaturated hydrocarbons undergo incomplete combustion due to a higher percentage of carbon, burning with a yellow, smoky, sooty flame.

Products of Combustion of a Saturated Hydrocarbon

When a saturated hydrocarbon (such as methane, $\mathrm{CH_4}$ ) undergoes complete combustion in the presence of oxygen, the products formed are:

Carbon dioxide ( $\mathrm{CO_2}$ )
Water vapour ( $\mathrm{H_2O}$ )
Heat and light

$\mathrm{CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + Heat\ and\ Light}$

clean blue flamesooty flameyellow flamecarbon dioxidewaterheat and lightcomplete combustion

Marking Scheme

1Distinction between saturated and unsaturated hydrocarbons using flame test (clean blue flame vs. yellow sooty flame) (1 mark)
2Listing the products of combustion of a saturated hydrocarbon (Carbon dioxide, water, heat, and light) (1 mark)

Hint

Think about the difference in the soot produced during combustion and write down the standard products of burning a fuel like methane.

Quick Oral Answer

Saturated hydrocarbons burn with a clean blue flame, while unsaturated ones burn with a yellow sooty flame. The products of complete combustion are carbon dioxide, water, heat, and light.

Analysis & Explanation

Saturated hydrocarbons contain only single covalent bonds and have a lower carbon-to-hydrogen ratio, allowing them to burn completely in the presence of atmospheric oxygen to produce a clean blue flame. Unsaturated hydrocarbons contain double or triple bonds and have a higher carbon content by mass. The oxygen in the air is insufficient for their complete combustion, leaving unburnt carbon particles that glow yellow and escape as black soot.

Common Mistakes

1Confusing the flame colors of saturated and unsaturated hydrocarbons.
2Forgetting to mention 'heat and light' as products of a combustion reaction.

Interesting Facts

If the air holes of a gas burner are blocked, even saturated hydrocarbons (like LPG) start burning with a yellow, sooty flame because of a limited supply of oxygen, which blackens the bottoms of cooking vessels.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2024?

This question carries 2 marks in the CBSE Class 10 Science 2024 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Saturated and Unsaturated Carbon Compounds" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2024 paper?

This is a Very Short Answer question from Section B in the CBSE Class 10 Science 2024 paper.