Reversing the calculations

4 marks · Normal

The table shows several solutions, each with a different number of moles and concentration.

Solution data
Solution	Moles (mol)	Concentration (mol/dm³)
A	0.00250	0.100
B	0.00800	0.200
C	0.00450	0.300
D	0.00180	0.0600

For each solution in the table, calculate and enter the volume (in cm³) needed to contain the given moles at the given concentration. Show your working for Solution A.

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) 25.0 cm³ · must show Working: volume = moles / concentration = 0.00250 / 0.100 = 0.0250 dm³ × 1000 = 25.0 cm³

(B) 40.0 cm³

(D) 30.0 cm³

Must show: Working shown for Solution A, Correct volumes for all solutions

Common mistakes: Forgetting to multiply by 1000 for cm³; Mixing up numerator and denominator

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Correct working shown for Solution A (volume = moles / concentration; conversion to cm³).

A1 · 1 mark · Correct volume for Solution A.

A2 · 1 mark · Correct volume for Solution B.

A3 · 1 mark · Correct volumes for both Solutions C and D.

Worked solution

A: volume = moles / concentration = 0.00250 / 0.100 = 0.0250 dm³ × 1000 = 25.0 cm³

B: 0.00800 / 0.200 = 0.0400 dm³ × 1000 = 40.0 cm³

C: 0.00450 / 0.300 = 0.0150 dm³ × 1000 = 15.0 cm³

D: 0.00180 / 0.0600 = 0.0300 dm³ × 1000 = 30.0 cm³