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

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

The chemical equation for the overall reaction is:

$NaHC{O}_{3\left(s\right)}$ + $C{H}_{3}COO{H}_{\left(l\right)}$ $\to$ $C{O}_{2\left(g\right)}$ + $H_2{O}_{\left(l\right)}$ + $N{a}_{\left(aq\right)}^{+}$ + $C{H}_{3}CO{O}^{-}\left(aq\right)$

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

Another common way to write this reaction is:

$NaHC{O}_3$ + $H{C}_2{H}_3{O}_2$ $\to$ $Na{C}_2{H}_3{O}_2$ + $H_{2}O$ + $C{O}_2$

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

$Pb(N{O}_3{)}_{2\left(aq\right)}$ + $2Kl$ $\to$ $Pb{l}_{2\left(s\right)}$ + $2KN{O}_{3\left(aq\right)}$

In this reaction, colour changes from colourless to yellow.

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

$BaC{l}_{2\left(aq\right)}$ + $N{a}_{2}S{O}_{4\left(aq\right)}$ $\to$ $BaS{O}_{4\left(s\right)}$ + $2NaC{l}_{\left(aq\right)}$

$BaS{O}_{4\left(s\right)}$- ppt

(d) Physical state

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

$Z{n}_{\left(s\right)}$ + $H_{2}S{O}_{4\left(aq\right)}$ $\to$ $ZnS{O}_{4\left(aq\right)}$ + $H_2$

In this reaction, heat is evolved