Question

9.) A 50 ml solution of unknown base contains 0.0012 mols of base (2.94 g/L) in solution.

Calculate the molar mass of the solution, and use that to calculate the concentration and

pH of the solution.

10.) Which of the 4 bases was the base from problem 9?

a) KOH

b) NaNH2

c) NH3

d) NaClO4

Answer 1

9) Find the mass of the unknown base:

m(base) = V*ρ_i/1000 = 50*2.95/1000 = 0.147 g

The molar mass of the solute = m(base)/n(base) = 0.147/0.0012 = 122.5 g/mol

Molar concentration of solution = 0.0012/0.050 = 0.024 mol/L

10) Calculate molar mass for following compounds:

a) M(KOH) = 56 g/mol

b) M(NaNH₂) = 39 g/mol

c) M(NH₃) = 17 g/mol

d) M(NaClO₄) = 122.5 g/mol

As we can see, the unknown base is (d) NaClO₄. NaClO4 solution has a neutral pH, the salt is formed by a strong base and a strong acid.

Answer: molar mass of the solute = 122.5 g/mol and molar concentration of solution = 0.024 mol/L. Unknown base is (d) NaClO₄ and solution has a neutral pH (pH = 7)