Question

Rank the following solutions from the highest [H3O+] (1) to the lowest [H3O+] (5).


[H3O+] = 3.16 × 10–4 M

[OH–] = 4.35 × 10–2 M

pH = 1.05

pOH = 7.0

pOH = 4.0

Answer 1

you can relate all of these values to each other by converting them all into pH.  pH=-log[H₃O⁺] and pH=14-pOH  (use pOH=-log[OH⁻])
pH=-log(3.16x10^-4 M H₃O⁺)=3.5
pH=14-(-log(4.35x10^-2))=12.64
pH=1.05
pH=14-7=7
pH=14-4=10
The smaller the pH is, the higher the concentration of H₃O⁺ is.
due to that 
the order from highest[H₃O⁺] to the lowest is: pH=1.05, [H₃O⁺]=3.16x10^-4M, pOH=7, pOH=4, and [OH⁻]=4.35x10^-2M

I hope this helps