Question

Calculate the ph and the poh of an aqueous solution that is 0.030 m in hcl(aq) and 0.070 m in hbr(aq) at 25°c.

Answer 1

Solution:

Since, both are strong acids. So both ionize 100% in solution.  

Let us consider that we have 1 liter of the solution. In it, we have 0.030 moles of H+ (from the HCl) and 0.070 moles of H+ (from the HBr) for a total of 0.100 mole in 1 liter. Here we ignore the chloride ion and the bromide ion since both acids ionize 100%. The only important ion (for pH) is the H+.  

In terms of just the H+, this is 0.100 M  

pH = - log 0.100 = 1.000  

And

pH + pOH = 14.000  

-1.000+14.000=13.000

Therefore,

pOH = 13.000