Question

The solution that will give a pH = 12.00 is (MW: NaOH = 40 g/mol):

A. 4.0 g NaOH in 1.0 L of solution.

B. 12 g NaOH in 1.0 L of solution.                                                                                            

C. 0.20 g NaOH in 2.0 L of solution.

D. 0.20 g NaOH in 0.50 L of solution.

E. 0.40 g NaOH in 0.10 L of solution.

Answer 1

pH = 12.0

pH + pOH 14

pOH = 14- pH = 14 - 12 = 2

[OH-] = 10^-2 = 0.01

So, Molarity of solution should be = 0.01 M

Molarity = No. of moles / volume of solution in Liter

a) Moles of NaOH = (4.0 g) / (40 g/mol) = 0.1 mol

Molarity = (0.1 mol) / (1.0 L) = 0.1 M

b)

Moles of NaOH = (12 g) / (40 g/mol) = 0.3 mol

Molarity = (0.3 mol) / (1 L) = 0.3 M

c)

moles of NaOH = (0.20 g) / (40 g/mol) = 0.005 mol

Molarity = (0.005 mol) / (2.0 L) = 0.0025 M

d)

moles of NaOH = (0.20 g) / (40 g/mol) = 0.005 mol

Molarity of NaOH = (0.005 mol) / (0.5 L) = 0.01 M

e)

Moles of NaOH = (0.4g) / (40 g/mol) = 0.01 mol

Molarity = (0.01 mol) / (0.10 L) = 0.1 M

Conditions for d are matching with Molarity

So; the solution given pH = 12 is D. 0.20 g NaOH in 0.50 L of solution.