pH 1 answer

Calculate the pH of 0.1 moldm^-3 hydrochloric acid.

Hydrochloric acid is a strong acid and so is totally disociated.

pH = -log₁₀[H⁺]    where [x] means concentration of x in moldm^-3 .

So,   pH = -log₁₀[0.1]

So,   pH = 1

If sufficient water is added to 10 cm³ of this acid to make a total volume of 1 dm³, what is the new pH?

10 cm³ of the original acid contains 10 x 0.1 / 1000 moles of acid.

This is 0.001 mol and so the concentration is 0.001 moldm^-3

and so as before,  pH = -log₁₀[0.001] and pH = 3