Question

0.50 g of sodium hydroxide (NaOH) pellets are dissolved in water to make 6.0 L of solution. What is the pH of this solution? Express the pH numerically to two decimal places.

Answer 1

mass of NaOH = 0.50 g

molar mass of NaOH = 40 g/mol

moles of NaOH = mass / molar mass

                         = 0.50 / 40

                         = 0.0125

volume = 6.0 L

molarity = moles / volume

             = 0.0125 / 6.0

            = 2.08 x 10^-3 M

[OH-] = 2.08 x 10^-3 M

pOH = -log [OH-] = -log ( 2.08 x 10^-3 )

pOH = 2.68

pH + pOH = 14

pH = 11.32