Video Transcript
Salts can be made by reacting various metal compounds with acids. With which acid would sodium hydroxide react to produce sodium chloride?
This question deals with the production of a salt. A salt is an ionic compound made of cations and anions. Salts can be produced through various types of reactions involving acids. A few examples of these types of reactions would be an acid–base reaction, the reaction between an acid and a metal, or a reaction between an acid and a carbonate compound. The question tells us that the compound reacting with an acid would be sodium hydroxide, which is a base, not a metal or carbonate compound. So we know the reaction taking place will be an acid–base reaction.
Let’s have a look at what occurs in an acid–base reaction. In this type of reaction, we can expect an acid to react with a base to form a salt and water. An example of this would be the reaction between sulfuric acid, or H2SO4, aqueous and potassium hydroxide, or two KOH, aqueous to form the soluble salt potassium sulfate, or K2SO4, aqueous and water.
Let’s have a closer look at this pattern so we can determine how sodium chloride, with a chemical formula of NaCl, can be formed from a reaction with our base, sodium hydroxide, with the chemical formula NaOH, and an acid whose chemical formula we do not yet know. We can see the salt formed in this example contains potassium cations, which originated from the base. So the salt formed in an acid–base reaction receives its cation from the reactant behaving as a base, while the anion of the salt, which in this case is the sulfate ion, originates from the substance behaving as an acid. So, in an acid–base reaction, the salt formed will acquire its anion from the substance behaving as an acid.
Using this pattern, let’s predict the acid that would react with sodium hydroxide to produce sodium chloride. We know that our base, sodium hydroxide, will be a reactant in this equation, with the soluble salt sodium chloride being a product, in addition to water. To find the chemical formula of our unknown acid, let’s use the chemical formula of our salt. We know that the sodium cations present in sodium chloride originated from our base, sodium hydroxide. Therefore, the chloride ions present in our salt must have originated from our acid. So our unknown acid must contain chloride ions.
To complete the chemical formula for our unknown acid, we can use the definition of a Brønsted–Lowry acid, which is a substance that does or can lose protons in a reaction, where protons in this definition refers to hydrogen ions. Therefore, our acid also contains hydrogen ions. So the chemical formula for our acid can be rewritten as HCl. HCl is the chemical formula for hydrochloric acid.
Therefore, the acid that would react with sodium hydroxide to produce sodium chloride is hydrochloric acid.
