Question

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

Answer 1

(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