pH values

9. A student carried out an investigation with aqueous solutions of nitric acid, sodium hydroxide, ethanoic acid and water.
The student diluted 0.015 mol dm–3 nitric acid with an equal volume of water and measured the pH of the diluted acid at 25 °C.
(a)(i) Calculate the pH of 0.015 mol dm–3 nitric acid.

The pH is 1.82 for the first one.

(ii) Calculate the pH of the diluted acid.

Can someone help me with ii please?

Reply 1

RMNDK

Original post by rm_27

The bit in bold is the key.
So let's say you have x volume of the acid. The moles would therefore be 0.015x.

You're adding an equal volume of water, i.e. x volume of water.
So the total volume would therefore be 2x.

The concentration has now changed. If you've got 0.015x moles in 2x volume, your concentration is 0.015x/2x = 0.0075moldm^-3

Simply put: same number of moles in double the volume you had. Therefore concentration must halve.

You can figure out pH from this.