Question

Calculate the pH of a solution containing 0.20 g of NaOH in 2,000. mL of solution.

Answer 1

NaOH is a strong base, which means it completely dissociates into OH- ions in water via this reaction:

NaOH -----> Na + OH

Find how the molarity of your compound:

.20g x 1 mole / 39.99 grams = .005 moles

.005 moles / 2.0 L = .0025 M

So the concentration of OH- in molarity has to be .0025M, since that's what the concentration of NaOH is -- it completely dissociates.

So we knows [OH-] = .0025

Find the pOH:

pOH = - log [OH-]

pOH = - log (.0025)

pOH = 2.60

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You should know pOH + pH = 14, so naturally.....

14 - pOH = pH

14 - 2.60 = pH

pH = 11.40