Question

What is the salt produced when sodium hydroxide (NaOH) reacts with sulfuric acid (H2SO4)?

Na2S
Na2H2
Na2SO3
Na2SO4

Answer 1

@Ciarán95 ?

Answer 2

Let's look at the reactants we are using here:
- sodium hydroxide is a base...we can identify this from the fact that it contains the OH- hydroxide ion (A base will dissociate in solution to produce OH- ions in the solution, according to the definition).
- sulfuric acid, as the name clearly suggests, is an acid. This is because it has two H+ ions to donate and, by definition, an acid will dissociate in solution to produce H+ ions in the solution.

So, we are dealing with a very straightforward reaction between an acid and a base. In such cases, we have a rule which we can use to predict what products will be formed:

\[acid + base \rightarrow salt + water\]

So, we know that H2O, water, will always form in this reaction.
\[H _{2}SO _{4} + NaOH \rightarrow ? + H _{2}O\]

This reaction is called a double displacement reaction, quite a common reaction when we have reactants which are composed of ions. These will be of the form:

\[AB + CD \rightarrow CB + AD\]
where A, B, C and D are the individual ions which make up the reactants:

- For sulfuric acid, it is composed of 1 negatively charged sulfate ion ((SO4)2-) balanced out by two positively charged hydrogen ions (H+).
-For sodium hydorxide, we have 1 negatively charged hydroxide ion (OH-) balanced out by 1 positively charged sodium ion (Na+).

We can see that the H+ from H2SO4 combines with the OH- from NaOH to form H2O. This leaves us with the Na+ from NaOH and the (SO4)2- from H2SO4 to combine to form the salt. However, like in the way the water molecules formed are neutral, the salt must be neutral also (i.e. it has no overall positive or negative charge). So, the salt molecules formed must be made up of two Na+ ions (creating a +2 charge) to cancel out the -2 charge from the (SO4)2- ion. This will leave us with a salt with the chemical formula:
\[Na _{2}SO _{4}\]
called sodium sulfate. Hope that helps! :)