Reaction scheme: 1. A + H2O --(electrolysis)--> X (caustic soda) + Y↑ (anode) + Z↑ (cathode) 2. A (molten) --(electrolysis)--> M (cathode) + Y↑ (anode) 3. M + CH3COOH → P + Z↑ 4. CH3COOH + Q --(conc. H2SO4)--> R 5. R + X → P + Q A Derive the names of A, Y, Z, M, P & R B Improvise an activity to test Z. C Name the process in which compounds X, Y & Z are formed from A. Justify your response.

ScienceCBSE Class 10 · Sample paper, session 2024-25 · 4 marks · Case-based

CBSE Class 10 Science sample paper 2024-25: question 37

From the official CBSE sample question paper for 2024-25, section E, question 37, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q37 · 4 marks · Case-basedCompetency-basedAcids, Bases and Salts

Reaction scheme:
1. A + H2O --(electrolysis)--> X (caustic soda) + Y↑ (anode) + Z↑ (cathode)
2. A (molten) --(electrolysis)--> M (cathode) + Y↑ (anode)
3. M + CH3COOH → P + Z↑
4. CH3COOH + Q --(conc. H2SO4)--> R
5. R + X → P + Q

A
Derive the names of A, Y, Z, M, P & R
0 marks
B
Improvise an activity to test Z.
0 marks
OR
C
Name the process in which compounds X, Y & Z are formed from A. Justify your response.
0 marks

Figure in the paper: Boxed reaction scheme of five reactions as listed in the stem. (Visually impaired version: A. Distinguish between ethanol and ethanoic acid experimentally. B. Give the IUPAC name of the first member of Alkene which is formed by addition of conc. sulphuric acid to it. Illustrate with a chemical equation. OR C. 'All combustion reactions are oxidation but all oxidation reactions are not combustion.' Justify.) See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

Open one hint at a time and try again before the next.

Hint 1

Caustic soda is NaOH. Which common salt solution gives NaOH on electrolysis?

Hint 2

At the cathode a positive ion or H⁺ is reduced; at the anode chloride ions are oxidised. Molten salt has no water.

Hint 3

An acid + an alcohol with conc. H₂SO₄ gives a sweet-smelling compound, and NaOH splits that compound back up.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

A. In reaction 1, electrolysis of an aqueous salt gives caustic soda (NaOH). This happens with brine, so A = sodium chloride (NaCl).
½ mark
In reaction 1:
$2NaCl (aq) + 2 H_{2} O (l) electrolysis 2NaOH (aq) + C l_{2} (g) + H_{2} (g)$
Chlorine is released at the anode, so **Y = chlorine gas ( $C l_{2}$ )**.
½ mark
Hydrogen is released at the cathode, so **Z = hydrogen gas ( $H_{2}$ )**.
½ mark
In reaction 2, electrolysis of molten NaCl gives sodium at the cathode (and $C l_{2}$ at the anode), so M = sodium metal (Na).
½ mark
In reaction 3, sodium reacts with ethanoic acid:
$2Na + 2C H_{3} COOH \to 2C H_{3} COONa + H_{2}$
So **P = sodium ethanoate ( $C H_{3} COONa$ )**.
½ mark
In reaction 4, an acid reacts with an alcohol Q (ethanol) in the presence of conc. $H_{2} S O_{4}$ . This is esterification:
$C H_{3} COOH + C_{2} H_{5} OH conc. H_{2} S O_{4} C H_{3} COO C_{2} H_{5} + H_{2} O$
So R = ethyl ethanoate (an ester).
Check with reaction 5: $C H_{3} COO C_{2} H_{5} + NaOH \to C H_{3} COONa + C_{2} H_{5} OH$ , which gives P and Q ✓.
½ mark
B. Activity to test Z (hydrogen):
1. Put zinc granules with dilute sulphuric acid in a test tube fitted with a cork and a delivery tube.
2. Pass the gas evolved into soap solution, so that soap bubbles filled with the gas form.
3. Bring a burning candle near a gas-filled bubble.
The gas burns with a pop sound, which confirms it is hydrogen:
$Zn + H_{2} S O_{4} \to ZnS O_{4} + H_{2}$
1 mark
C. (Alternative to B) The process is the chlor-alkali process. It is named after its products: chlorine and an alkali, sodium hydroxide (with hydrogen as a by-product). They are formed when electricity is passed through aqueous NaCl (brine).
1 mark

Answer: A: A = sodium chloride, Y = chlorine, Z = hydrogen, M = sodium, P = sodium ethanoate, R = ethyl ethanoate (ester); B: hydrogen from Zn + dil. H₂SO₄ burns with a pop sound; OR C: chlor-alkali process, named after its products chlorine and alkali (NaOH)

Where the marks are

Identifies A as sodium chloride (0.5 mark)
Identifies Y as chlorine gas (0.5 mark)
Identifies Z as hydrogen gas (0.5 mark)
Identifies M as sodium metal (0.5 mark)
Identifies P as sodium ethanoate (0.5 mark)
Identifies R as ethyl ethanoate/ester (0.5 mark)
B: Describes an activity in which hydrogen burns with a pop sound (1 mark), OR C: Names the chlor-alkali process and justifies the name from its products (1 mark)

Revise the chapter

Chapter: Acids, Bases and Salts (notes, formulas, where marks are lost and every past question)

Practise this chapterBoard-style questions from Acids, Bases and Salts, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: every question, by section.

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CBSE Class 10 Science sample paper 2024-25: question 37

Hints

Step-by-step solution

Revise the chapter

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