Chemists use mathematics.

Sometimes they use simple arithmetic to balance chemical equations. For example, we know that burning hydrogen with oxygen makes water:

H_{2} + O_{2} → H_{2}O

But that equation is wrong, since there is only one oxygen on the right side, but there were two on the left side. So we use arithmetic to balance the equation:

2 H_{2} + O_{2} → 2 H_{2}O

Chemists use simple mathematics to deal with ratios and proportions, units and dimensions, and simple statistics. They plot graphs of their observations and results.

Chemists also use more advanced mathematics to deal with rates of change in chemical reactions, to find maximums and minimums, or other extremes or inflection points.

While mathematics is used a lot in chemistry, most of the mathematics is fairly simple. The mathematics in physics is generally more involved, and in physical chemistry you might find more higher mathematics in use than in many of the other branches of chemistry. The nature of the problem is usually what determines the tools needed to solve it.