Question

28. A concentrated ammonia solution has a density of 0.900 g/mL at 25°C and is 14.8 M. What is the percent by mass of NH3 in the solution? a. 28.0% NH3 by mass b. 18.9% NH3 by mass c. 0.6% NHz by mass d. 9.7% NH3 by mass e. 1.6% NH3 by mass wal. 1 2

Answer 1

Given

Molarity of concentrated ammonia solution = 14.8 M

Density of ammonia solution = 0.900 g /ml.

We have, density = Mass / Volume

On rearranging above formula , we get Mass = density $\times$ volume

$\therefore$ Mass of 1000 ml ( 1 L ) ammonia solution = 0.900 g / ml $\times$ 1000 ml = 900 g

We have, Molarity = No. of moles of solute / volume of solution in L

$\therefore$ No. of moles of solute = Molarity $\times$ volume of solution in L

$\therefore$ No. of moles of NH ₃ = 14.8 mol / L $\times$ 1 L = 14.8 mol

We have, No. of moles = Mass / Molar mass

$\therefore$ Mass = No. of moles $\times$ Molar mass

$\therefore$ Mass of NH ₃ = 14.8 mol $\times$ ( 17.03 g/mol ) = 252.04 g

We know that, % W =[ Mass of solute / Mass of solution ] 100

% W NH ₃ = [ 252.04 g / 900 g ] 100 = 28.0 % NH ₃ by mass

ANSWER : 28.0 % NH ₃ by mass