Practise Concentrations in mol/dm³. 15 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Calculate the amount, in moles, of MOH in each 25.0 cm3 portion.
0.00250 mol
A student dissolves 0.40 mol of a salt in water to make 2.0 dm3 of solution. Calculate the concentration of the solution.
0.2 mol/dm3
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
The concentration of a solution in mol/dm3 can be calculated using the equation: concentration in mol/dm3 = amount of solute in mol ÷ volume of solution in dm3
(a) A student dissolved 0.50 mol of sodium chloride in water to make 2.0 dm3 of solution. Calculate the concentration of the solution.[2]
(b) Calculate the amount, in moles, of hydrochloric acid in 0.500 dm3 of a solution with a concentration of 2.0 mol/dm3.[2]
Show the answer and mark scheme
(a)Answer: 0.25 mol/dm3
0.50 ÷ 2.0
0.25 (mol/dm3)
(b)Answer: 1.0 mol
2.0 × 0.500
1.0 (mol)
Question 2Medium6 marks
Sodium hydroxide, NaOH, dissolves in water to form an alkaline solution. Relative atomic masses (Ar): H = 1, O = 16, Na = 23
(a) Calculate the amount, in moles, of sodium hydroxide in 25.0 cm3 of a 0.200 mol/dm3 solution.[2]
(b) A student dissolved 4.0 g of sodium hydroxide in water and made the solution up to 250 cm3. Calculate the concentration of the solution in mol/dm3.[3]
(c) Calculate the concentration, in g/dm3, of the sodium hydroxide solution the student made.[1]
Show the answer and mark scheme
(a)Answer: 0.00500 mol
25.0 cm3 = 0.0250 dm3
0.200 × 0.0250 = 0.00500 (mol)
(b)Answer: 0.40 mol/dm3
moles of NaOH = 4.0 ÷ 40 = 0.10
250 cm3 = 0.250 dm3
0.10 ÷ 0.250 = 0.40 (mol/dm3)
(c)Answer: 16 g/dm3
16 (g/dm3)
Question 3Hard5 marks
A student titrated 25.0 cm3 of sodium hydroxide solution with hydrochloric acid of concentration 0.100 mol/dm3. NaOH + HCl → NaCl + H2O The mean titre of hydrochloric acid was 20.00 cm3.
(a) Calculate the amount, in moles, of hydrochloric acid in 20.00 cm3.[1]
(b) Calculate the concentration of the sodium hydroxide solution in mol/dm3.[2]
(c) Calculate the concentration of the sodium hydroxide solution in g/dm3. Mr of NaOH = 40[2]