If 0.561 g of KOH is dissolved in water to give 200 mL of solution at 298 K. Calculate the concentrations of potassium, hydrogen and hydroxyl ions. What is its pH?

Explanation

Molarity of a solution is given by
` " " w= ( M xx M. xx V)/(1000)`
` therefore 0.561 = ( M xx 56 xx 200)/(1000) ( because ` mol mass of KOH = 56)
or ` " " M= (0.561 xx 1000)/(56 xx 200) = 0.05 ` M
Since , KOH dissociates completely in solutions.
` KOH to K^(+) + OH^(-)`
` therefore [K^(+) ] =[OH^(-)] = " Molarity of KOH " = 0.05 M`
and ` " " [H^(+) ] = (K_w)/([OH^(-)]) = (1.0 xx 10 ^(-14))/(0.05) = 2.0 xx 10 ^(-13) M.`