Allied solutions

Allied solutions

Grade 8

Chemical Reactions | Exercise

Question 1

Q1) State what is a chemical reaction. A chemical reaction is often accompanied by external indications or characteristics which include - (a) Colour change (b) Effervescence or gas evolved © Evolution or absorption of heat (d) Formation of a precipitate. With reference to each of the above indications, state the external indication seen during - (i) addition of dilute acid to active metal (ii) Addition of dilute hydrochloric acid to silver nitrate (iii) Addition of water to quicklime (iv) Thermal decomposition of mercury oxide.

Solution:

A chemical reaction is a chemical change where substances react with each other to form a new substance.

(i) addition of dilute acid to an active metal - The test tube becomes hot and hydrogen gas is evolved, which means heat is produced.

(ii) Addition of dilute hydrochloric acid to silver nitrate - A white coloured precipitate is formed which is AgCl

(iii) Addition of water to quicklime - The solution boils and heat is produced accompanied by a hissing sound.

(iv) Thermal decomposition of mercury oxide - The colour of mercury changes from red to silvery, that is metallic.

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Question 1

Q1) State what is a chemical reaction. A chemical reaction is often accompanied by external indications or characteristics which include - (a) Colour change (b) Effervescence or gas evolved © Evolution or absorption of heat (d) Formation of a precipitate. With reference to each of the above indications, state the external indication seen during - (i) addition of dilute acid to active metal (ii) Addition of dilute hydrochloric acid to silver nitrate (iii) Addition of water to quicklime (iv) Thermal decomposition of mercury oxide.

Solution:

A chemical reaction is a chemical change where substances react with each other to form a new substance.

(i) addition of dilute acid to an active metal - The test tube becomes hot and hydrogen gas is evolved, which means heat is produced.

(ii) Addition of dilute hydrochloric acid to silver nitrate - A white coloured precipitate is formed which is AgCl

(iii) Addition of water to quicklime - The solution boils and heat is produced accompanied by a hissing sound.

(iv) Thermal decomposition of mercury oxide - The colour of mercury changes from red to silvery, that is metallic.

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subject-cta
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