Write one chemical equation each for the chemical reaction in which the following have taken place : (i) Change in colour (ii) Change in temperature (iii) Formation of precipitate Mention colour change/temperature change (rise/fall)/compound precipitated along with equation.

Chemical Reactions and Equations

Characteristics of Chemical Reactions

Official Answer

Based on the NCERT text, here are the chemical equations and observations:

(i) Change in colour: Heating of Ferrous sulphate crystals.

$2\text{FeSO}_4(\text{s}) \xrightarrow{\text{Heat}} \text{Fe}_2\text{O}_3(\text{s}) + \text{SO}_2(\text{g}) + \text{SO}_3(\text{g})$

Observation: The green colour of ferrous sulphate crystals changes to reddish-brown (ferric oxide).

(ii) Change in temperature: Reaction between Quick lime and water.

$\text{CaO}(\text{s}) + \text{H}_2\text{O}(\text{l}) \rightarrow \text{Ca}(\text{OH})_2(\text{aq}) + \text{Heat}$

Observation: Rise in temperature (Exothermic reaction), making the container warm.

(iii) Formation of precipitate: Reaction between Barium chloride and Sodium sulphate.

$\text{BaCl}_2(\text{aq}) + \text{Na}_2\text{SO}_4(\text{aq}) \rightarrow \text{BaSO}_4(\text{s}) + 2\text{NaCl}(\text{aq})$

Observation: Formation of a white insoluble substance (precipitate) of Barium sulphate.

Ferrous sulphatereddish-brownQuick limeexothermicBarium sulphateprecipitateinsoluble

Marking Scheme

11 mark for colour change: correct equation and mentioning green to reddish-brown.
21 mark for temperature change: correct equation and mentioning rise in temperature/heat evolved.
31 mark for precipitate: correct equation and mentioning insoluble barium sulphate.

Hint

Recall Activity 1.4 for temperature change and Activity 1.5 for color change from your textbook.

Quick Oral Answer

A change in temperature occurs in exothermic reactions like adding water to lime. A precipitate is an insoluble solid formed in a reaction, like white barium sulphate.

Analysis & Explanation

Chemical reactions are characterized by observable changes. (i) In the thermal decomposition of ferrous sulphate, the loss of water of crystallization and formation of ferric oxide causes a color shift from green. (ii) The reaction of calcium oxide with water is highly exothermic, releasing energy as heat. (iii) A double displacement reaction between two salt solutions often results in an insoluble solid called a precipitate, as seen with barium sulphate.

Common Mistakes

1Writing the equation without state symbols (though often accepted, state symbols make it more informative).
2Confusing exothermic (heat release) with endothermic (heat absorption).
3Not specifying the actual color change (e.g., just saying 'color changes').

Interesting Facts

The chemical formula for marble is also $\text{CaCO}_3$ , which is related to the product formed when slaked lime reacts with $\text{CO}_2$ on walls.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2024?

This question carries 3 marks in the CBSE Class 10 Science 2024 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 "Characteristics of Chemical Reactions" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2024 paper?

This is a Short Answer question from Section C in the CBSE Class 10 Science 2024 paper.