List the important products of the Chlor-alkali process. Write one important use of each.

Acids, Bases and Salts

Washing Soda

Official Answer

Washing soda is prepared by the recrystallization of sodium carbonate.

Chemical Equation:

$Na_2CO_3(s) + 10H_2O(l) \rightarrow Na_2CO_3 \cdot 10H_2O(s)$

Type of Salt:

It is a basic salt.

Type of Hardness of Water Removed:

It is used to remove permanent hardness of water.

RecrystallizationSodium carbonate decahydrateBasic saltPermanent hardnessWater of crystallization

Marking Scheme

1Stating that washing soda is prepared by the recrystallization of sodium carbonate. (0.5 marks)
2Writing the balanced chemical equation: $Na_2CO_3 + 10H_2O \rightarrow Na_2CO_3 \cdot 10H_2O$ (1 mark)
3Identifying the salt as a basic salt. (0.5 marks)
4Identifying that it removes permanent hardness of water. (1 mark)

Hint

Recall that washing soda is sodium carbonate decahydrate ( $Na_2CO_3 \cdot 10H_2O$ ) and is a basic salt used to treat hard water.

Quick Oral Answer

Q: What is the chemical formula of washing soda? A: The chemical formula of washing soda is $Na_2CO_3 \cdot 10H_2O$ . Q: Why does washing soda turn red litmus blue? A: Because it is a basic salt formed from a strong base ( $NaOH$ ) and a weak acid ( $H_2CO_3$ ), and its aqueous solution is alkaline.

Analysis & Explanation

Washing soda ( $Na_2CO_3 \cdot 10H_2O$ ) is a sodium salt containing ten molecules of water of crystallization. When anhydrous sodium carbonate (soda ash) is treated with water, it undergoes recrystallization, which is a highly controlled hydration process. Because it is formed from a strong alkali ( $NaOH$ ) and a weak acid ( $H_2CO_3$ ), its aqueous solution undergoes hydrolysis to yield hydroxide ions ( $OH^-$ ), making it basic. It is highly effective in removing permanent hardness of water caused by dissolved chlorides and sulfates of calcium and magnesium by precipitating them as insoluble carbonates.

Common Mistakes

1Writing the chemical formula of washing soda as $Na_2CO_3$ instead of $Na_2CO_3 \cdot 10H_2O$ .
2Confusing permanent hardness with temporary hardness.
3Classifying washing soda as an acidic or neutral salt.

Interesting Facts

Anhydrous sodium carbonate ( $Na_2CO_3$ ) is commonly known as 'soda ash'.

Washing soda is widely used in the glass, soap, and paper industries, as well as a cleaning agent for domestic purposes.

Spotted a mistake or something unclear?

Tell us — we fix reported answers fast.

Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2020?

This question carries 3 marks in the CBSE Class 10 Science 2020 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 "Washing Soda" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2020 paper?

This is a Short Answer question from Section B in the CBSE Class 10 Science 2020 paper.