# Calculate the pH of a strong acid

What is the pH of a 0.015 M solution of hydrochloric acid (HCl)?

a) 1.8

b) 12.2

c) 5.6

d) 2.1

e) 13.1

#### Solution Preview

What is the pH of a 0.015 M solution of hydrochloric acid (HCl)?

a) 1.8

b) 12.2

c) 5.6

d) 2.1

e) 13.1

********************************************************************************

Short answer: The correct answer is (a) 1.8.

*********************************************************************************

Step by step answer:

The formula (or equation) for calculating pH is shown below, and it is one that you should become familiar with and commit to memory. It is unlikely that a professor or instructor will provide this formula on an exam.

pH = -log [H+]

Formally, this formula defines "pH" as the "negative log of the concentration of hydrogen ions".

Practically, in order to use this formula, you must have a basic understanding of your solution (e.g. 0.015 M hydrogen chloride in this question), and how to determine the concentration of hydrogen ions in your solution before you can proceed to calculate pH.

***EXAM TIP*** For this pH equation, the concentration of H+ MUST be in units of M (i.e. molarity, also referred to as mole/L). Always check your ...

#### Solution Summary

The solution provides a quick answer as well as a step by step solved answer to help students of introductory chemistry, biochemistry, and health or medical sciences understand the concept of calculating pH. Bonus: 'exam tips' to help students avoid mistakes or to help check whether their exam answers 'make sense'.