Q4.32P - Chemistry: Molecular Nature Of Matter And Change

Question

When each of the following pairs of aqueous solutions is mixed, does a precipitation reaction occur? If so, write balanced molecular, total ionic, and net ionic equations:

 (a) Potassium carbonate + barium hydroxide

 (b) Aluminium nitrate + sodium phosphate

 

Step-by-Step Solution

Answer

(a) A precipitation reaction occurs. The precipitate formed is barium carbonate.

(b) A precipitation reaction occurs. The precipitate formed is Aluminium phosphate. 

Step 1: Rules to determine the charge on the ions

We note the ions present in the reactants for each pair of solutions and write the cation-anion combinations if any of them are insoluble or soluble. For the molecular equation, we predict the products:

1. All common metal hydroxides are insoluble, except those of Group 1A (1) and the larger members of Group 2A (2) (beginning with ${\mathrm{Ca}}^{2+}$ ).

2. All common carbonates $\left({\text{CO}}_{\text{3}}^{\text{2-}}\right)$ and phosphates $\mathbf{\left(}{\mathbf{\text{PO}}}_{\mathbf{\text{4}}}^{\mathbf{\text{3-}}}\mathbf{\right)}$ are insoluble, except those of Group 1A (1) and  ${\mathbf{\text{NH}}}_{\mathbf{\text{4}}}^{\mathbf{\text{+}}}\mathbf{.}$

3. All common sulfides are insoluble except those of Group 1A (1), Group 2A (2), and ${\mathbf{\text{NH}}}_{\mathbf{\text{4}}}^{\mathbf{\text{+}}}\mathbf{.}$

 

Step 2: Write the equation of potassium carbonate and barium hydroxide

The balanced molecular reaction is:

$\left(\mathrm{a}\right){\mathrm{K}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)+\mathrm{Ba}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)\to {\mathrm{BaCO}}_3\left(\mathrm{s}\right)+2\mathrm{KOH}\left(\mathrm{aq}\right)$

The total ionic equation is:

 ${\text{2K}}^{\text{+}}\left(\text{aq}\right){\text{\hspace{0.17em}+CO}}_{\text{3}}^{\text{-2}}\left(\text{aq}\right){\text{+Ba}}^{\text{+2}}{\text{(aq)+2OH}}^{\text{-}}\text{(aq)}\to {\text{\hspace{0.17em}2K}}^{\text{+}}{\text{(aq)+2OH}}^{\text{-}}{\text{(aq)+BaCO}}_{\text{3}}\left(\text{s}\right)$

The net ionic equation is:

${\mathrm{Ba}}^{2+}\left(\mathrm{aq}\right)+\left({{\mathrm{CO}}_3}^{2-}\right)\left(\mathrm{aq}\right)\to {\mathrm{BaCO}}_3\left(\mathrm{s}\right)$

 Barium carbonate is insoluble in water and forms precipitate.

Step 3: Write the equation of aluminium nitrate and sodium phosphate

The balanced molecular reaction is:

$\left(\mathrm{b}\right)\mathrm{Al}{\left({\mathrm{NO}}_3\right)}_3\left(\mathrm{aq}\right)+{\mathrm{Na}}_3{\mathrm{PO}}_4\left(\mathrm{aq}\right)\to 3{\mathrm{NaNO}}_3\left(\mathrm{aq}\right)+{\mathrm{AlPO}}_4\left(\mathrm{s}\right)$

The total ionic equation is:

 ${\mathrm{Al}}^{3+}\left(\mathrm{aq}\right)+3{{\mathrm{NO}}_3}^{-}\left(\mathrm{aq}\right)+3\mathrm{Na}\to \left(\mathrm{aq}\right)+{\mathrm{PO}}_4^{-3}\left(\mathrm{aq}\right){\mathrm{AlPO}}_4\left(\mathrm{s}\right)+3{\mathrm{Na}}^{+}\left(\mathrm{aq}\right)+3{{\mathrm{NO}}_3}^{-}\left(\mathrm{aq}\right)$

The net ionic equation is:

${\mathrm{Al}}^{3+}\left(\mathrm{aq}\right)+{\mathrm{PO}}_4^{3-}\left(\mathrm{aq}\right)\to {\mathrm{AlPO}}_4\left(\mathrm{s}\right)$

 

Alumunium phosphate is insoluble in aqueous solution and forms precipitate.