Question

A reaction will NOT occur when all the reactants and products in the ionic equation are spectator ions because no change occurs such as the formation of a precipitate or molecular compound. Which of the following combinations (as reactants) will NOT undergo chemical change when mixed?
A. Mg(NO3)2(aq) and NaOH(aq)
B. HCl(aq) and NaOH(aq)
C. NaNO3(aq) and KI(aq)

Answer 1

Answer: The correct answer is Option A and C.

Explanation:

Net ionic equation of any reaction does not include any spectator ions.

Spectator ions are defined as the ions which does not get involved in a chemical equation. They are found on both the sides of the chemical reaction when it is present in ionic form.

For the given options:

• Option A: $Mg(NO_3)_2(aq.)\text{ and }NaOH(aq.)$

The chemical equation for the reaction of magnesium nitrate and sodium hydroxide is given as:

$Mg(NO_3)_2(aq.)+2NaOH(aq.)\rightarrow Mg(OH)_2(aq.)+2NaNO_3(aq.)$

Ionic form of the above equation follows:

$Mg^{2+}(aq.)+2NO_3^-(aq.)+2Na^+(aq.)+2OH^-(aq.)\rightarrow Mg^{2+}(aq.)+2OH^-(aq.)+2Na^+(aq.)+2NO_3^-(aq.)$

As, all the ions are present on both the sides of the reaction. Thus, it will not be present in the net ionic equation and are spectator ions.

Hence, the chemical reaction does not take place.

• Option B: $HCl(aq.)\text{ and }NaOH(aq.)$

The chemical equation for the reaction of hydrochloric acid and sodium hydroxide is given as:

$HCl(aq.)+NaOH(aq.)\rightarrow NaCl(aq.)+H_2O(l)$

Ionic form of the above equation follows:

$H^{+}(aq.)+Cl^-(aq.)+Na^+(aq.)+OH^-(aq.)\rightarrow Na^{+}(aq.)+Cl^-(aq.)+H_2O(l)$

As, sodium and hydroxide ions are present on both the sides of the reaction. Thus, it will not be present in the net ionic equation and are spectator ions.

The net ionic equation for the above reaction follows:

$H^+(aq.)+OH^-(aq.)\rightarrow H_2O(l)$

Hence, the chemical reaction take place.

• Option C: $NaNO_3(aq.)\text{ and }KI(aq.)$

The chemical equation for the reaction of sodium nitrate and potassium iodide is given as:

$NaNO_3(aq.)+KI(aq.)\rightarrow KNO_3(aq.)+NaI(aq.)$

Ionic form of the above equation follows:

$Na^{+}(aq.)+NO_3^-(aq.)+K^+(aq.)+I^-(aq.)\rightarrow K^{+}(aq.)+NO_3^-(aq.)+Na^+(aq.)+I^-(aq.)$

As, all the ions are present on both the sides of the reaction. Thus, it will not be present in the net ionic equation and are spectator ions.

Hence, the chemical reaction does not take place.

Thus, the correct answer is Option A and C.

Answer 2

I think the correct answer from the choices listed above is option C. The substances that do not undergo chemical change when mixed are the substances  NaNO3(aq) and KI(aq). They form spectator ions. Hope this answers the question.