Q4.50 - Chemistry: Molecular Nature Of Matter And Change

Question

Question: Zinc hydroxide is insoluble in water but dissolves when a nitric acid solution is added. Why? Write balanced total ionic and net ionic equations, showing nitric acid as it actually exists in water and the reaction as a proton-transfer process.

Step-by-Step Solution

Answer

Answer

 

Zinc hydroxide is insoluble in water but dissolves when a nitric acid solution is added because it is an acid-base reaction and nitrate ions readily displace$OH$ ions from zinc hydroxide.

 

Step 1: Determine different types of equations to represent aqueous ionic reactions

The molecular equation reveals the least about the species in solution and is actually somewhat misleading because it shows all the reactants and products as if they were intact undissociated compounds.

The total ionic equation is a much more accurate representation of the reaction because it shows all the soluble ionic substances dissociated into ions.

The net ionic equation is the most useful because it omits the spectator ions and shows the actual chemical change taking place.

 

Step 2: Write the net ionic equation of the reaction between zinc hydroxide and nitric acid

Balanced molecular reaction:

 $\mathrm{Zn}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+2{\mathrm{HNO}}_3\left(\mathrm{aq}\right)\to \mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_2\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

The total ionic equation:

 $\mathrm{Zn}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)+2{\mathrm{NO}}_3^{-}\left(\mathrm{aq}\right)\to {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)+2{\mathrm{NO}}_3^{-}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

The net ionic equation:

 $\mathrm{Zn}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)+2{\mathrm{H}}^{+}\left(\mathrm{aq}\right)\to {\mathrm{Zn}}^{2+}\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$