Write the chemical reaction where the following changes are observed.

(a) Gas is evolved

(b) Colour change is noticed

(c) Precipitate is formed

(d) Physical state is changed

[4 marks]

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Solution

(a) Reaction between baking soda and vinegar. Baking soda on reaction with vinegar produces carbon dioxide.

The chemical equation for the overall reaction is:

$N a H C O_{3 (s)}$ + $C H_{3} C O O H_{(l)}$ $\to$ $C O_{2 (g)}$ + $H_{2} O_{(l)}$ + $N a_{(a q)}^{+}$ + $C H_{3} C O O^{-} (a q)$

with s = solid, l = liquid, g = gas, aq = aqueous or in water solution

Another common way to write this reaction is:

$N a H C O_{3}$ + $H C_{2} H_{3} O_{2}$ $\to$ $N a C_{2} H_{3} O_{2}$ + $H_{2} O$ + $C O_{2}$ [1 mark]

(b) Change in colour: Reaction between lead nitrate solution and potassium iodide solution.

$P b (N O_{3})_{2 (a q)}$ + $2 K l$ $\to$ $P b l_{2 (s)}$ + $2 K N O_{3 (a q)}$

In this reaction, colour changes from colourless to yellow. [1 mark]

(c) Formation of precipitate: Action of barium chloride on sodium sulphate.

$B a C l_{2 (a q)}$ + $N a_{2} S O_{4 (a q)}$ $\to$ $B a S O_{4 (s)}$ + $2 N a C l_{(a q)}$

$B a S O_{4 (s)}$ - ppt. [1 mark]

(d) Physical state

Change in temperature: Action of dilute sulphuric acid on zinc.

$Z n_{(s)}$ + $H_{2} S O_{4 (a q)}$ $\to$ $Z n S O_{4 (a q)}$ + $H_{2}$

In this reaction, heat is evolved. [1 mark]

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Write the chemical reaction where the following changes are observed. (a) Gas is evolved (b) Colour change is noticed (c) Precipitate is formed (d) Physical state is changed [4 marks]

Write the chemical reaction where the following changes are observed.

(a) Gas is evolved

(b) Colour change is noticed

(c) Precipitate is formed

(d) Physical state is changed

[4 marks]