Question

Express the concentration of a 0.0560 M aqueous solution of fluoride, F–, in mass percentage and in parts per million. Assume the density of the solution is 1.00 g/mL.

Answer 1

consider 100 ml of solution

now

we know that

moles = molarity x volume (L)

so

moles of F- = 0.056 x 100 x 10-3

moles of F- = 5.6 x 10-3

now

mass = moles x molar mass

so

mass of F- = 5.6 x 10-3 x 19

mass of F- = 0.1064 g

now

mass of solution = volume x density

mass of solution = 100 x 1

mass of solution = 100 g

now

% mass = mass of F- x 100 / mass of solution

so

% mass = 0.1064 x 100 / 100

% mass = 0.1064

now

ppm = mass of F- in mg / volume of solution (L)

so

ppm = 106.4 / 0.1

ppm = 1064 mg / L

so

parts per million is 1064