To solve this problem, we need to use the pH formula:
pH = -log[H+]
where [H+] represents the concentration of hydrogen ions in moles per liter (M).
To find [H+], we can rearrange the formula:
[H+] = 10^(-pH)
Substituting pH = 3.69, we get:
[H+] = 10^(-3.69) = 2.21 × 10^(-4) M
Since hydrochloric acid is a strong acid, it completely dissociates in water to give hydrogen ions and chloride ions:
HCl(aq) → H+(aq) + Cl-(aq)
Therefore, the concentration of hydrochloric acid required to give a solution with a pH of 3.69 is also 2.21 × 10^(-4) M.