Question

What is the h+ concentration for an aqueous solution with poh = 3.35 at 25 ∘c? express your answer to two significant figures and include the appropriate units?

Answer 1

POH value was calculated by the negative logarithm of hydroxide ion concentration.
To know the hydrogen ion concentration, we need to know the pH value, that can be found out if pOH is known 
pH + pOH = 14
pH = 14 - pOH 
pH = 10.65
once the pH is known we have to find the antilog. 
[H⁺] = antilog (-pH)
antilog can be found by 
[H⁺] = 10^(-10.65)
[H⁺] = 2.2 x 10⁻¹¹ M