Question 273 marksShort AnswerSection C

$Silver chloride kept in a china dish turns grey in sunlight. (a) Write the colour of silver chloride when it was kept in the china dish. (b) Name the type of chemical reaction taking place and write the chemical equation for the reaction. (c) State one use of the reaction. Name one more chemical which can be used for the same purpose.$

Q: Silver chloride kept in a china dish turns grey in sunlight. (a) Write the colour of silver chloride when it was kept in the china dish. (b) Name the type of chemical reaction taking place and write the chemical equation for the reaction. (c) State one use of the reaction. Name one more chemical which can be used for the same purpose.

(a) The colour of silver chloride when kept in the china dish is **white**. (b) The type of chemical reaction taking place is a **photolytic decomposition reaction** (or photochemical decomposition). The balanced chemical equation is: $$2\text{AgCl(s)} \xrightarrow{\text{Sunlight}} 2\text{Ag(s)} + \text{Cl}_2\text{(g)}$$ (c) **Use of the reaction**: This reaction is used in **black and white photography**. **Another chemical** that can be used for the same purpose is **silver bromide** ($\text{AgBr}$).

Chemical Reactions and Equations

Decomposition Reaction

Official answer

2\text{AgCl(s)} \xrightarrow{\text{Sunlight}} 2\text{Ag(s)} + \text{Cl}_2\text{(g)}

white

photolytic decomposition

silver chloride

silver bromide

black and white photography

sunlight

Marking scheme

1. $State the initial colour of silver chloride as white: 0.5 mark$
2. $Identify the reaction as photolytic decomposition: 0.5 mark$
3. $Write the balanced chemical equation with state symbols: 1 mark$
4. $State the use (black and white photography) and name silver bromide: 1 mark$

Hint

$Refer to Activity 1.8 in the textbook. Think about what happens to silver halides when exposed to sunlight.$

Quick oral answer

$Silver chloride is initially white and turns grey in sunlight due to photolytic decomposition into silver metal and chlorine gas. This reaction, along with the decomposition of silver bromide, is used in black and white photography.$

Common mistakes

1. $\text{Cl}_2$
2. $Forgetting to balance the chemical equation.$
3. $Not mentioning 'sunlight' over the reaction arrow.$

Analysis and explanation

When white silver chloride is exposed to sunlight, it absorbs light energy and decomposes into grey-coloured silver metal and chlorine gas. This is a classic example of photolytic decomposition, where a single reactant breaks down into simpler substances in the presence of light. Silver bromide behaves similarly and is also used in photographic films.

Interesting facts

$Transition lenses in eyeglasses use a similar photochemical principle, where silver halides embedded in the glass react to sunlight, darkening the lenses to protect your eyes!$

Question details

Q27 of 39 questions

Board: CBSE
Class: Class 10
Subject: Science
Year: 2023
Section: Section C
Marks: 3
Type: Short Answer
Chapter: Chemical Reactions and Equations
Topic: $Decomposition Reaction$
Bloom's level: Remembering
Syllabus topic: $Decomposition reactions (Photolytic decomposition)$

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Frequently asked questions

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

$This question carries 3 marks in the CBSE Class 10 Science 2023 examination.$

$Which chapter does this question come from in Science?$

$This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.$

$What topic does this question cover in Science?$

$This question covers the topic "Decomposition Reaction" from CBSE Class 10 Science.$

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

$This is a Short Answer question from Section C in the CBSE Class 10 Science 2023 paper.$