Dilution question

Question: Calculate the pH of the solutions formed in the following way by adding water to 25cm3 of 1.50 mol dm-3 HCl to make 250cm3 of solution.

The answer is 0.82 but I’m not sure how to get there

Reply 1

username5443984

Original post by LunaBraun

Question: Calculate the pH of the solutions formed in the following way by adding water to 25cm3 of 1.50 mol dm-3 HCl to make 250cm3 of solution.
The answer is 0.82 but I’m not sure how to get there

What has happened to the volume with respect to ratios when you compare the initial volume and final volume? It is a 1:10 ratio right?

The number of moles of HCl hasn't changed i.e. it is still whatever 1.5 x (25/1000) gives us but since the volume has increased by 10 times, the concentration of HCl decreases by 10 times.

HCl is mono-protic so we only have to consider one H.

-log₁₀[H⁺] = pH

so therefore pH = 0.82 when we sub in 0.15 as [H⁺].