Concentrations of solutions
4 marks · Normal| Sample | Concentration (mol/dm³) | Volume used (dm³) |
|---|---|---|
| A | 0.10 | 0.020 |
| B | 0.20 | 0.015 |
| C | 0.40 | 0.025 |
Which sample contains the largest amount of sodium sulfate? Show your calculations.
State the amount in mol present in that sample.
Suggest one reason why a higher concentration solution may have less sodium sulfate than a lower concentration solution.
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) Sample C contains the largest amount; calculation: 0.40 × 0.025 = 0.010 mol
(b) 0.010 mol
(c) Because a smaller volume of a higher concentration can have less total amount; amount depends on both volume and concentration.
Also accept: Alternative reasoning for (c)
Common mistakes: Not multiplying concentration by volume; Selecting highest concentration instead of amount
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Correctly calculates amount for all three samples (amount = c × V)
A1 (a) · 1 mark · Identifies correct sample (C) with working shown
A2 (b) · 1 mark · States amount in correct units (0.010 mol)
B1 (c) · 1 mark · Provides correct explanation for amount being less in higher concentration solution if volume is less
Worked solution
Calculate amount for each:
A: 0.10 × 0.020 = 0.002 mol
B: 0.20 × 0.015 = 0.003 mol
C: 0.40 × 0.025 = 0.010 mol
Sample C contains the largest amount: 0.010 mol.
A higher concentration solution may have less sodium sulfate overall if the volume used is smaller.