3.8 Concentration of solutions in g/dm³
5 exam questions worth 9 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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How many cm3 are there in 1 dm3?
Choose one answer.
Correct Not quite: the answer is 1000
Mark scheme
C
Model answer
C: 1 dm3 = 1000 cm3.
8.0 g of sodium hydroxide is dissolved in water to make 200 cm3 of solution.
Calculate the concentration in g/dm3.
Mark scheme
- volume = 200 ÷ 1000 = 0.20 dm3 (1)
- 8.0 ÷ 0.20 = 40 g/dm3 (1)
Model answer
Volume = 0.20 dm3, so concentration = 8.0 ÷ 0.20 = 40 g/dm3.
Calculate the mass of copper sulfate in 25 cm3 of a solution with a concentration of 80 g/dm3.
Mark scheme
- 25 cm3 = 0.025 dm3 (1)
- 80 × 0.025 = 2.0 g (1)
Model answer
mass = 80 × 0.025 = 2.0 g
A student dissolves 10 g of salt in 500 cm3 of solution, then adds water to make the volume 1000 cm3.
Describe and explain how the concentration changes.
Mark scheme
- the concentration halves / falls from 20 to 10 g/dm3 (1)
- the same mass of solute is in double the volume (1)
Model answer
The concentration halves, from 20 g/dm3 to 10 g/dm3, because the same mass of salt is now spread through twice the volume.
What volume of solution, in cm3, contains 3.0 g of solute if the concentration is 60 g/dm3?
Mark scheme
- volume = 3.0 ÷ 60 = 0.050 dm3 (1)
- = 50 cm3 (1)
Model answer
volume = mass ÷ concentration = 0.050 dm3 = 50 cm3.
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