Q4.34P - 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) Sodium sulfide + nickel (II) sulfate 

(b) Lead (II) nitrate + potassium bromide

Step-by-Step Solution

Answer

(a) Yes, pairs of aqueous solutions are mixed, does a precipitation reaction.

(b) Yes, pairs of aqueous solutions are mixed, does a precipitation reaction.

Step 1: Rules to determine the charge on the ions

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 ${\mathbf{\text{Ca}}}^{\mathbf{\text{2+}}}$ ).

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

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

4. All common chlorides $\mathbf{\left(}{\mathbf{\text{Cl}}}^{\mathbf{\text{-}}}\mathbf{\right)}\mathbf{\text{,}}$ bromides  $\mathbf{\left(}{\mathbf{\text{Br}}}^{\mathbf{\text{-}}}\mathbf{\right)}\mathbf{\text{,}}$and iodides $\mathbf{\left(}{\mathbf{\text{I}}}^{\mathbf{\text{-}}}\mathbf{\right)}\mathbf{\text{,}}$ are soluble, except those of ${\mathbf{\text{Ag}}}^{\mathbf{\text{+}}}{\mathbf{\text{,\hspace{0.17em}Pb}}}^{\mathbf{\text{2+}}}{\mathbf{\text{,\hspace{0.17em}Cu}}}^{\mathbf{\text{+}}}{\mathbf{\text{,\hspace{0.17em}and\hspace{0.17em}Hg}}}_{\mathbf{\text{2}}}^{\mathbf{\text{2+}}}\mathbf{\text{.}}$

Step 2: Write the equation of sodium sulfide and nickel (II) sulfate

The balanced molecular reaction is:

${\mathbf{\text{(a) Na}}}_{\mathbf{\text{2}}}{\mathbf{\text{S(aq) + NiSO}}}_{\mathbf{\text{4}}}\mathbf{\text{(aq)}}\mathbf{\to }{\mathbf{\text{NiS(s) + Na}}}_{\mathbf{\text{2}}}{\mathbf{\text{SO}}}_{\mathbf{\text{4}}}\mathbf{\text{(aq)}}$

The total ionic equation is:

${\mathbf{\text{2Na}}}^{\mathbf{\text{+}}}{\mathbf{\text{(aq) + S}}}^{\mathbf{\text{2-}}}{\mathbf{\text{(aq) + Ni}}}^{\mathbf{\text{2+}}}{\mathbf{\text{(aq) + SO}}}_{\mathbf{\text{4}}}^{\mathbf{\text{2-}}}\mathbf{\text{(aq)}}\mathbf{\to }{\mathbf{\text{NiS(s) + 2Na}}}^{\mathbf{\text{+}}}{\mathbf{\text{(aq) + SO}}}_{\mathbf{\text{4}}}^{\mathbf{\text{2-}}}\mathbf{\text{(aq)}}$

The net ionic equation is:

${\mathbf{\text{Ni}}}^{\mathbf{\text{2+}}}{\mathbf{\text{(aq) + S}}}^{\mathbf{\text{2-}}}\mathbf{\text{(aq)}}\mathbf{\to }\mathbf{\text{NiS(s)}}$

Step 3: Write the equation of lead (II) nitrate and potassium bromide

The balanced molecular reaction is:

${\mathbf{\text{(b) Pb(NO}}}_{\mathbf{\text{3}}}{\mathbf{\text{)}}}_{\mathbf{\text{2}}}\mathbf{\text{(aq) + 2KBr(aq)}}\mathbf{\to }{\mathbf{\text{KNO}}}_{\mathbf{\text{3}}}{\mathbf{\text{(aq) + PbBr}}}_{\mathbf{\text{2}}}\mathbf{\left(}\mathbf{\text{s}}\mathbf{\right)}$

The total ionic equation is:

${\mathbf{\text{Pb}}}^{\mathbf{\text{2+}}}{\mathbf{\text{(aq) + 2NO}}}_{\mathbf{\text{3}}}^{\mathbf{\text{-}}}{\mathbf{\text{(aq) + 2K}}}^{\mathbf{\text{+}}}{\mathbf{\text{(aq) + 2Br}}}^{\mathbf{\text{-}}}\mathbf{\text{(aq)}}\mathbf{\to }{\mathbf{\text{2K}}}^{\mathbf{\text{+}}}{\mathbf{\text{(aq) + 2NO}}}_{\mathbf{\text{3}}}^{\mathbf{\text{-}}}{\mathbf{\text{(aq) + PbBr}}}_{\mathbf{\text{2}}}\mathbf{\text{(s)}}$

The net ionic equation is:

${\mathbf{\text{Pb}}}^{\mathbf{\text{2+}}}{\mathbf{\text{(aq) + 2Br}}}^{\mathbf{\text{-}}}\mathbf{\text{(aq)}}\mathbf{\to }{\mathbf{\text{PbBr}}}_{\mathbf{\text{2}}}\mathbf{\text{(s)}}$