1 markMCQSection A

Select washing soda from the following:

Acids, Bases and Salts

Salts and their derivatives

Options

(a)

\mathrm{NaHCO}_3

(b)

\mathrm{Na}_2\mathrm{CO}_3 \cdot 5\mathrm{H}_2\mathrm{O}

(c)

\mathrm{Na}_2\mathrm{CO}_3 \cdot 10\mathrm{H}_2\mathrm{O}

(d)

\mathrm{NaOH}

Official Answer

The correct option is (c). Washing soda is sodium carbonate decahydrate, represented by the chemical formula $Na_2CO_3 \cdot 10H_2O$ .

Washing sodaSodium carbonate decahydrateNa2CO3.10H2O

Marking Scheme

1Identification of the correct option (c) (1 mark)

Hint

Washing soda is a sodium carbonate salt containing ten molecules of water of crystallization.

Quick Oral Answer

The chemical formula of washing soda is sodium carbonate decahydrate, written as $Na_2CO_3 \cdot 10H_2O$ .

Analysis & Explanation

Washing soda is a sodium-derived salt obtained by recrystallization of sodium carbonate. Its chemical formula is $Na_2CO_3 \cdot 10H_2O$ (sodium carbonate decahydrate), where the $10H_2O$ represents the ten molecules of water of crystallization.

Option (a) is incorrect because $NaHCO_3$ is the chemical formula for baking soda (sodium hydrogencarbonate).
Option (b) is incorrect because washing soda specifically contains ten molecules of water of crystallization ( $10H_2O$ ), not five ( $5H_2O$ ).
Option (d) is incorrect because $NaOH$ is sodium hydroxide (caustic soda), which is a strong base, not a carbonate salt.

Common Mistakes

1Confusing washing soda ( $Na_2CO_3 \cdot 10H_2O$ ) with baking soda ( $NaHCO_3$ ).
2Selecting the incorrect number of water molecules of crystallization (e.g., choosing $5H_2O$ instead of $10H_2O$ ).

Interesting Facts

The ten water molecules in washing soda are not 'wet' water; they are part of the crystal structure (water of crystallization) that gives the salt its crystalline shape.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2023?

This question carries 1 mark in the CBSE Class 10 Science 2023 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Acids, Bases and Salts" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Salts and their derivatives" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2023 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2023 paper.