The pH scale for acidity is defined by pH=−log10[H+]

Question

 The pH scale for acidity is defined by pH=−log10[H+] where [H+] is the concentration of hydrogen ions measured in moles per liter (M). A solution has a pH of 3.9. Calculate the concentration of hydrogen ions in moles per liter (M).

The concentration of hydrogen ions is  moles per liter.

Answer 1

pH = −log₁₀[H+]

Substitute in the given pH value:

3.9 = −log₁₀[H+]

Muliply both sides by -1:

-3.9 = log₁₀[H+]

Take both sides to the power 10:

10^-3.9 = [H+]

0.0001258925 = [H+]

Concentration of H+ ions, moles per liter.

In scientific notation, this would be 1.26 × 10^-4 moles per liter.

Answer 2

The question should have been posted in the Chemistry section but here's the solution!

In order to find [H+], we need to rearrange the equation to solve for [H+], which we can do so:

1) pH = -log₁₀[H+]

-pH = log₁₀[H+]

[H+] = 10^-pH

2) Now we can solve, which is finding the concentration of hydrogen ions in a pH of 3.9

[H+] = 10^-3.9

We get the concentration of hydrogen ions [H+] is 1.3 * 10^-4 M