Question

Write the net ionic equation to show the formation of a precipitate (insoluble salt) when the following solutions are mixed. Write none if no insoluble salt forms. (12.3)
a.Pb(NO3)2(aq) + NaBr(aq)

Answer 1

Answer:

Pb²⁺(aq) + 2Br⁻(aq) ⟶ PbBr₂(s)  

Explanation:

A. Molecular equation

Pb(NO₃)₂(aq) + 2NaBr(aq) ⟶ PbBr₂(?) + 2NaNO₃(?)

To predict whether there is a precipitate, we must remember some solubility rules:

1. Salts containing Na⁺ are soluble  
2. Salts containing Br⁻ are generally soluble. An important exception to this rule is that PbBr₂ is insoluble.

Thus, the molecular equation is

Pb(NO₃)₂(aq) + 2NaBr(aq) ⟶ PbBr₂(s) + 2NaNO₃(aq)

B. Ionic equation

We write all the soluble substances as ions.

Pb²⁺(aq) + 2NO₃⁻(aq) + 2Na⁺(aq) + 2Br⁻(aq) ⟶ PbBr₂(s) + 2Na⁺(aq) + 2NO₃⁻(aq)

C. Net ionic equation

To get the net ionic equation, we cancel the ions that appear on each side of the ionic equation.

Pb²⁺(aq) + 2NO₃⁻(aq) + 2Na⁺(aq) + 2Br⁻(aq) ⟶ PbBr₂(s) + 2Na⁺(aq) + 2NO₃⁻(aq)

The net ionic equation is

Pb²⁺(aq) + 2Br⁻(aq) ⟶ PbBr₂(s)