Concentrations of solutions

3 marks · Easy

(a)

Give the formula that links concentration (in mol/dm³), amount of substance (in mol), and volume of solution (in dm³).

[1 mark]

(b)

A student dissolves 0.080 mol of potassium nitrate (KNO₃) in enough water to make 0.40 dm³ of solution.

(i)

Calculate the concentration of this potassium nitrate solution in mol/dm³.

[2 marks]

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

(a) concentration = amount / volume · must show c = n / V

(b(i)) 0.20 mol/dm³

Common mistakes: Using volume in cm³ instead of dm³; Using amount in grams instead of moles

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · Correct formula given (e.g. c = n / V or equivalent).

M1 (b(i)) · 1 mark · Uses the correct formula: concentration = amount / volume.

A1 (b(i)) · 1 mark · Correct answer: 0.20 mol/dm³ (accept correct answer to 2 sig fig or better). (follow-through)

Worked solution

a) The formula is concentration = amount of substance / volume of solution, or c = n / V.

b) i) amount = 0.080 mol; volume = 0.40 dm³