Question

What are the spectator ions when hydrochloric acid reacts with sodium hydroxide?

a) Na + and H +

b) Cl – and OH –

c) H + and OH –

d) Na + and Cl –

Answer 1

The answer is option (d) Na⁺ and Cl^-

Firstly Spectator ions are the ions which exist in the same form on both the reactant and product side of the chemical reaction. These ions are unchanged on both sides of the reaction and will not affect the equilibrium. Also these ions don't undergo chemical change at all and are not included in net ionic equation.

The reaction when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) is

HCl (aq) + NaOH (aq) ---> NaCl(aq) + H₂O (l)

Consider the first reactant: HCl (aq) ----> H⁺ (aq) + Cl^- (aq)

Consider the second reactant: NaOH (aq) -----> Na⁺ (aq) + OH^- (aq)

Consider the first product: NaCl (aq) ----> Na⁺ (aq) +  Cl^- (aq)

Now the complete ionic equation for HCl (aq) + NaOH (aq) ---> NaCl(aq) + H₂O (l) is

H⁺ (aq) + Cl^- (aq) + Na⁺ (aq) + OH^- (aq) -----> Na⁺ (aq) + Cl^- (aq) + H₂O (l)

The common ions on both reactant and product side are Na⁺ and Cl^- ions. These are the spectator ions.

The net ionic equation is: H⁺ (aq) + OH^- (aq) ----->  H₂O (l)

So the answer is (d) Na⁺ and Cl^-