What is the pH of a solution that is comprised of 0.0843 M HCl and 0.0287 M HClO4?

Answer 1

Both acids are monoprotic acids and both are strong acids.

So 0.0843 M HCl will give 0.0843 M H+
and
0.0287 M HClO4 will give 0.0287 M H+

so the total H+ is

(0.0843+0.0287)M = 0.113 M

pH=-log([H+]/M)
so pH=-log(0.113)