2 marksShort AnswerSection A

Write the structural formula of ethanol. What happens when it is heated with excess of conc. H₂SO₄ at 443 K? Write the chemical equation for the reaction stating the role of conc. H₂SO₄ in this reaction.

Q: Write the structural formula of ethanol. What happens when it is heated with excess of conc. H₂SO₄ at 443 K? Write the chemical equation for the reaction stating the role of conc. H₂SO₄ in this reaction.

### 1. Structural Formula of Ethanol $$\begin{array}{ccccc} \text{H} & & \text{H} & & \\ | & & | & & \\ \text{H}-\text{C} & - & \text{C} & - & \text{O}-\text{H} \\ | & & | & & \\ \text{H} & & \text{H} & & \end{array}$$ (or represented as $CH_3-CH_2-OH$) ### 2. Reaction with Excess Conc. $H_2SO_4$ at $443\text{ K}$ When ethanol is heated with excess concentrated sulphuric acid at $443\text{ K}$, it undergoes dehydration (removal of water) to form ethene (an unsaturated hydrocarbon). ### 3. Chemical Equation $$CH_3CH_2OH \xrightarrow{\text{Hot conc. } H_2SO_4, 443\text{ K}} CH_2=CH_2 + H_2O$$ ### 4. Role of Conc. $H_2SO_4$ Concentrated sulphuric acid acts as a **dehydrating agent** in this reaction, as it removes a water molecule from ethanol.

Carbon and its Compounds

Chemical Properties of Carbon Compounds

Official Answer

1. Structural Formula of Ethanol

$\begin{array}{ccccc} \text{H} & & \text{H} & & \\ | & & | & & \\ \text{H}-\text{C} & - & \text{C} & - & \text{O}-\text{H} \\ | & & | & & \\ \text{H} & & \text{H} & & \end{array}$

(or represented as $CH_3-CH_2-OH$ )

2. Reaction with Excess Conc. $H_2SO_4$ at $443\text{ K}$

When ethanol is heated with excess concentrated sulphuric acid at $443\text{ K}$ , it undergoes dehydration (removal of water) to form ethene (an unsaturated hydrocarbon).

3. Chemical Equation

$CH_3CH_2OH \xrightarrow{\text{Hot conc. } H_2SO_4, 443\text{ K}} CH_2=CH_2 + H_2O$

4. Role of Conc. $H_2SO_4$

Concentrated sulphuric acid acts as a dehydrating agent in this reaction, as it removes a water molecule from ethanol.

ethanol structural formulaethenedehydrationdehydrating agentCH2=CH2443 K

Marking Scheme

1Correct structural formula of ethanol: 0.5 mark
2Statement of what happens (formation of ethene): 0.5 mark
3Balanced chemical equation with conditions: 0.5 mark
4Stating the role of conc. $H_2SO_4$ as a dehydrating agent: 0.5 mark

Hint

Heating ethanol with concentrated acid at $443\text{ K}$ removes a water molecule to form an alkene.

Quick Oral Answer

When ethanol is heated with excess concentrated sulphuric acid at $443\text{ K}$ , it gets dehydrated to form ethene. Here, concentrated sulphuric acid acts as a dehydrating agent.

Analysis & Explanation

Ethanol ( $CH_3CH_2OH$ ) contains an $-OH$ group. When treated with a strong dehydrating agent like concentrated $H_2SO_4$ at a high temperature of $443\text{ K}$ ( $170^\circ\text{C}$ ), an intramolecular elimination reaction occurs. A hydrogen atom from the methyl carbon and the hydroxyl group from the adjacent carbon are eliminated as a water molecule ( $H_2O$ ), creating a double bond between the two carbon atoms to form ethene ( $CH_2=CH_2$ ).

Common Mistakes

1Writing the temperature incorrectly (e.g., $413\text{ K}$ instead of $443\text{ K}$ , which yields ether instead of ethene).
2Forgetting to specify that the sulphuric acid must be concentrated and hot.
3Drawing the structure of ethane instead of ethene as the product.

Interesting Facts

Concentrated sulphuric acid has a very strong affinity for water, so much so that it can tear apart hydrogen and oxygen atoms from organic molecules to form water, leaving behind carbon or unsaturated compounds.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2017?

This question carries 2 marks in the CBSE Class 10 Science 2017 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 "Chemical Properties of Carbon Compounds" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2017 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2017 paper.