Consider the reaction ZnO plus 2HCl. What is the name of the salt produced during this reaction?
This question is asking us to identify the salt product from the reaction between zinc oxide and hydrochloric acid. A salt is an ionic compound made of cations and anions. Salts can be produced in many types of reactions with acids. A few examples include acid–base reactions, reactions between acids and metals, and reactions between acids and carbonate compounds.
In this reaction, hydrochloric acid is reacting with the base zinc oxide. Let’s have a look at an example of an acid–base reaction. When the base magnesium oxide reacts with hydrobromic acid, magnesium bromide and water are formed. The salt produced in this reaction is magnesium bromide. This salt is made up of magnesium cations, which originated from the basic reactant magnesium oxide. The salt also contains bromide ions, which originated from the acidic reactant hydrobromic acid. This reaction also forms water.
So in an acid–base reaction, the salt product is formed from the cations of the base and the anions of the acid. Using this pattern, let’s predict what salt would be formed from the reaction between zinc oxide and hydrochloric acid. We know that one product of this acid–base reaction would be water. To determine the name of the salt formed, let’s have a look at the ions it will be composed of. We know that the base zinc oxide will contribute its cations to the salt, which are zinc two plus cations. We know that the acid will contribute its anions, which are chloride ions. This compound is made of zinc two plus ions and chloride one minus ions.
In order to have a neutrally charged compound, we need two chloride ions for every one zinc ion, giving us the formula ZnCl2. This salt composed of zinc and chloride ions would be called zinc chloride. Therefore, the name of the salt produced during this reaction is zinc chloride.