An acid 'X' present in tamarind when mixed with 'Y', produces a mixture 'Z'. 'Z' on addition to a dough when heated makes cakes soft and spongy. 'Y' is prepared from common salt and helps in faster cooking. (i) Write the common names of 'X', 'Y' and 'Z', and the chemical formula of 'Y'. (ii) How is 'Y' prepared and how does it help in making cakes soft and spongy? Illustrate the reaction with suitable chemical equation. (iii) Write the name and chemical formula of a mild base other than 'Y' used as an antacid.

(i) X tartaric acid, Y baking soda (NaHCO_3), Z baking powder; (ii) NaCl + H_2O + CO_2 + NH_3 → NH_4Cl + NaHCO_3; NaHCO_3 + H^+ → CO_2 + H_2O + sodium salt, and the released CO_2 makes the cake spongy; (iii) Magnesium hydroxide, Mg(OH)_2.

ScienceCBSE Class 10 · Board exam 2024, set 31/5/1 · 5 marks · Long answer

CBSE Class 10 Science 2024: question 34(b)

Set in the CBSE Class 10 board exam of 2024, paper 31/5/1, section D, question 34(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q34(b) · 5 marks · Long answerAcids, Bases and Salts

An acid 'X' present in tamarind when mixed with 'Y', produces a mixture 'Z'. 'Z' on addition to a dough when heated makes cakes soft and spongy. 'Y' is prepared from common salt and helps in faster cooking.

(i)
Write the common names of 'X', 'Y' and 'Z', and the chemical formula of 'Y'.
1 mark
(ii)
How is 'Y' prepared and how does it help in making cakes soft and spongy? Illustrate the reaction with suitable chemical equation.
2 marks
(iii)
Write the name and chemical formula of a mild base other than 'Y' used as an antacid.
2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/5/1.

Hints

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

Hint 1

Baking powder is a mixture of a mild edible acid and a sodium salt that gives off a gas.

Hint 2

Y is made from brine, ammonia and $C O_{2}$ . Which gas, released in the dough, would puff up the cake?

Hint 3

For the antacid, recall the 'milk' sold in chemist shops for acidity.

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.

(i) X = tartaric acid (the acid in tamarind).
½ mark
Y = baking soda.
½ mark
Z = baking powder (baking soda + tartaric acid).
½ mark
Chemical formula of Y: $NaHC O_{3}$ (sodium hydrogencarbonate).
½ mark
(ii) Preparation: common salt (brine) reacts with water, carbon dioxide and ammonia:
$NaCl + H_{2} O + C O_{2} + N H_{3} \to N H_{4} Cl + NaHC O_{3}$
1 mark
In the dough, on heating/wetting, baking soda reacts with the acid of baking powder:
$NaHC O_{3} + H^{+} \to C O_{2} + H_{2} O + Sodium salt of acid$
½ mark
The $C O_{2}$ gas released forms bubbles in the dough, which make the cake rise and become soft and spongy. The tartaric acid neutralises the bitter sodium carbonate that would otherwise form.
½ mark
(iii) Mild base used as an antacid: magnesium hydroxide (milk of magnesia), $Mg (OH)_{2}$ .
1 mark

Answer: (i) X tartaric acid, Y baking soda ( $N a H C O_{3}$ ), Z baking powder; (ii) $N a C l + H_{2} O + C O_{2} + N H_{3} \to N H_{4} C l + N a H C O_{3}$ ; $N a H C O_{3} + H^{+} \to C O_{2} + H_{2} O$ + sodium salt, and the released $C O_{2}$ makes the cake spongy; (iii) Magnesium hydroxide, $M g (O H)_{2}$ .

Where the marks are

Names X as tartaric acid (½ mark)
Names Y as baking soda (½ mark)
Names Z as baking powder (½ mark)
Gives the formula $N a H C O_{3}$ (½ mark)
Writes the preparation equation from NaCl, $H_{2} O$ , $C O_{2}$ and $N H_{3}$ (1 mark)
Writes the reaction of $N a H C O_{3}$ with acid giving $C O_{2}$ (½ mark)
Explains that the $C O_{2}$ released makes the cake soft and spongy (½ mark)
Names magnesium hydroxide with formula $M g (O H)_{2}$ (1 mark)

Revise the chapter

Chapter: Acids, Bases and Salts (notes, formulas, where marks are lost and every past question)
Topic: Baking Soda, Washing Soda and Plaster of Paris

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 paper2024 board paper, set 31/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.

CBSE Class 10 Science 2024: question 34(b)

Hints

Step-by-step solution

Revise the chapter

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