Identify the spectator ions for the reaction that occurs when aqueous solutions of lithium sulfide and copper (ii) nitrate are mixed.

a. cu2 + and no3-

b. li + and cu2+

c. li + and no3-

d. s2 - and cu2+

e. no spectator ions are present.

The answer: c) Li⁺ and NO₃⁻

Firstly, we have to show molecular equation (all compounds are showed as neutral molecules) for the reaction:

Li₂S (aq) + Cu (NO₃) ₂ (aq) ⇒ CuS (s) + 2LiNO₃ (aq)

Then, the reaction has to be written as an ionic equation:

2Li⁺ (aq) + S²⁻ (aq) + Cu²⁺ (aq) + 2NO₃⁻ (aq) → CuS (s) + 2Li⁺ (aq) + 2NO₃⁻ (aq)

Soluble ionic compounds Li₂S and Cu (NO₃) ₂ are shown as dissociated ions. As you can see on both side of the equation we have Li⁺ and NO₃⁻ ions. They do not participate in the reaction, and they are called spectator ions. All the above is an ionic equation.

Finally, when we cancel out spectator ions, it remains just ions and molecules involved in the reaction and we get the net ionic equation:

S²⁻ (aq) + Cu²⁺ (aq) → CuS (s)