2 marksShort AnswerSection A

A compound ‘X’ on heating with excess conc. sulphuric acid at 443 K gives an unsaturated compound ‘Y’. ‘X’ also reacts with sodium metal to evolve a colourless gas ‘Z’. Identify ‘X’, ‘Y’ and ‘Z’. Write the equation of the chemical reaction of formation of ‘Y’ and also write the role of sulphuric acid in the reaction.

Q: A compound ‘X’ on heating with excess conc. sulphuric acid at 443 K gives an unsaturated compound ‘Y’. ‘X’ also reacts with sodium metal to evolve a colourless gas ‘Z’. Identify ‘X’, ‘Y’ and ‘Z’. Write the equation of the chemical reaction of formation of ‘Y’ and also write the role of sulphuric acid in the reaction.

The compounds and gas are identified as follows: - **X** is Ethanol ($CH_3CH_2OH$ or $C_2H_5OH$) - **Y** is Ethene ($CH_2=CH_2$ or $C_2H_4$) - **Z** is Hydrogen gas ($H_2$) ### Chemical Equation for the Formation of 'Y': $$CH_3CH_2OH \xrightarrow{\text{Hot conc. } H_2SO_4, 443\text{ K}} CH_2=CH_2 + H_2O$$ ### Role of Concentrated Sulphuric Acid: 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

The compounds and gas are identified as follows:

X is Ethanol ( $CH_3CH_2OH$ or $C_2H_5OH$ )
Y is Ethene ( $CH_2=CH_2$ or $C_2H_4$ )
Z is Hydrogen gas ( $H_2$ )

Chemical Equation for the Formation of 'Y':

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

Role of Concentrated Sulphuric Acid:

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

EthanolEtheneHydrogenDehydrating agentDehydration443 K

Marking Scheme

1Identification of X as Ethanol, Y as Ethene, and Z as Hydrogen gas (1 mark)
2Correct balanced chemical equation for the dehydration of ethanol (0.5 marks)
3Stating the role of concentrated sulphuric acid as a dehydrating agent (0.5 marks)

Hint

Think of an alcohol containing two carbon atoms that undergoes dehydration to form an alkene, and releases hydrogen gas when treated with active metals like sodium.

Quick Oral Answer

Q: What gas is evolved when sodium metal is dropped into ethanol? A: Hydrogen gas is evolved, which burns with a characteristic 'pop' sound.

Analysis & Explanation

This question tests the understanding of the chemical properties of ethanol, a key carbon compound. Ethanol undergoes dehydration (loss of a water molecule) when heated with excess concentrated sulphuric acid at $443\text{ K}$ to form ethene, an unsaturated hydrocarbon containing a carbon-carbon double bond. The reaction with sodium metal is a characteristic test for alcohols, where the acidic hydrogen of the hydroxyl group ( $-OH$ ) is replaced by sodium, releasing flammable hydrogen gas ( $H_2$ ).

Common Mistakes

1Writing the formula of ethene as ethane ( $C_2H_6$ ) instead of ethene ( $C_2H_4$ ).
2Forgetting to mention the temperature ( $443\text{ K}$ ) or the word 'concentrated' for sulphuric acid in the reaction conditions.
3Identifying gas 'Z' as carbon dioxide ( $CO_2$ ) or oxygen ( $O_2$ ) instead of hydrogen ( $H_2$ ).

Interesting Facts

Ethanol is a major constituent of all alcoholic beverages and is also used as an industrial solvent and increasingly as a biofuel blended with petrol.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2018?

This question carries 2 marks in the CBSE Class 10 Science 2018 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 2018 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2018 paper.