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) The pH of pure water is 7.0. Calculate the concentration of hydrogen ions in moles per liter (M).
(B) The pH of rainwater is 5.5. Calculate the concentration of hydrogen ions in moles per liter (M).
a) Calculate the concentration of hydrogen ions in pure water.
b) Calculate the concentration of hydrogen ions in rainwater.
c) Determine the pH of pure water.
d) Determine the pH of rainwater.

Answer 1

The concentration of hydrogen ions in pure water is 1 × 10-7 M, and the pH of pure water is 7.0. The concentration of hydrogen ions in rainwater is 3.16 × 10-6 M, and the pH of rainwater is 5.5.

Step-by-step explanation:

The concentration of hydrogen ions dissociating from pure water is 1 × 10-7 moles H+ ions per liter of water. The pH is calculated as the negative of the base 10 logarithm of this concentration. The log10 of 1 × 10-7 is -7.0, and the negative of this number yields a pH of 7.0, which is also known as neutral pH.

The pH of rainwater is 5.5. To calculate the concentration of hydrogen ions in moles per liter (M), we use the formula pH = -log10 [H+]. Rearranging the formula, we get [H+] = 10-pH. Substituting the pH value of 5.5, we get [H+] = 10-5.5 = 3.16 × 10-6 M.