AQA GCSE Chemistry Foundation (8462), Foundation tier · Quantitative chemistry › Concentration of solutions
Practise Concentration of solutions. 9 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.
Concentration tells you how much solute is dissolved in a given volume of solution. Here it is measured in grams per dm3 (g/dm3). You must calculate concentrations and masses of solute, and convert cm3 to dm3.
Key facts
Concentration (g/dm3) = mass (g) ÷ volume (dm3)
Mass (g) = concentration × volume (dm3)
Volume (dm3) = mass ÷ concentration
1 dm3 = 1000 cm3
cm3 → dm3: divide by 1000
Notes
What concentration means
Many reactions take place in solutions. A solution is a solute dissolved in a solvent.
The concentration of a solution can be measured as the mass of solute per volume of solution, in g/dm3.
1 dm3 = 1000 cm3 (1 litre). To convert cm3 to dm3, divide by 1000.
Calculations
concentration (g/dm3) = mass of solute (g) ÷ volume of solution (dm3)
mass of solute (g) = concentration (g/dm3) × volume (dm3)
Example: 5.0 g of sodium chloride is dissolved to make 250 cm3 of solution. Volume = 250 ÷ 1000 = 0.250 dm3. Concentration = 5.0 ÷ 0.250 = 20 g/dm3.
Example: the mass of solute in 50 cm3 of a 40 g/dm3 solution = 40 × 0.050 = 2.0 g.
How to answer each type of question
Calculate the concentration
2 to 3 marksGrade 5
Convert the volume to dm3 (÷ 1000).
Divide the mass in grams by the volume in dm3.
Give the unit, g/dm3.
Example. A student dissolved 3.0 g of copper sulfate in water to make 200 cm3 of solution. Calculate the concentration of the solution in g/dm3. [3 marks]
Using the volume in cm3 without dividing by 1000, which makes the concentration 1000 times too small.
Multiplying by 1000 instead of dividing when converting cm3 to dm3.
Using the volume of water added instead of the final volume of the solution.
Leaving out the unit, or writing g/cm3 instead of g/dm3.
More tips
Memory tricks
Formula triangle: mass on top, concentration × volume underneath.
Unit check: g ÷ dm3 = g/dm3. If the units do not come out right, the formula is upside down.
A dm3 is 1000 times bigger than a cm3, so the number in dm3 is always 1000 times smaller.
Sense check: if the volume is less than 1 dm3, the concentration is a bigger number than the mass.
Exam technique
Write the conversion to dm3 as its own line of working: it is often a mark.
Give the unit g/dm3 with every concentration.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Recall the unit of concentrationMass of solute per volume of solution, usually grams per dm3 (g/dm3).
Grade 4
Convert cm3 to dm3Divide by 1000, e.g. 250 cm3 = 0.250 dm3.
Grade 5
Calculate concentration in g/dm3Concentration = mass of solute (g) ÷ volume of solution (dm3).
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
concentration in g/dm3 = mass of solute in g ÷ volume of solution in dm3 How many cm3 are there in 0.250 dm3?
250 cm3
Name the piece of apparatus used to weigh the solid solute accurately.
(electronic) balance
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
The concentration of a solution can be calculated using the equation: concentration in g/dm3 = mass of solute in g ÷ volume of solution in dm3
(a) A student dissolved 12 g of sodium chloride in water to make 0.50 dm3 of solution. Calculate the concentration of the solution.[2]
(b) How many cm3 are there in 1 dm3?[1]
(c) Calculate the mass of solute in 2.0 dm3 of a solution with a concentration of 15 g/dm3.[2]
Show the answer and mark scheme
(a)Answer: 24 g/dm3
12 ÷ 0.50
24 (g/dm3)
(b)Answer: 1000
1000
(c)Answer: 30 g
15 × 2.0
30 (g)
Question 2Medium6 marks
Many chemical reactions take place in solutions. The concentration of a solution can be measured in g/dm3.
(a) A student dissolved 5.0 g of copper sulfate in water to make 250 cm3 of solution. Calculate the concentration of the solution in g/dm3.[2]
(b) Calculate the mass of sodium hydroxide in 25.0 cm3 of a solution with a concentration of 40 g/dm3.[2]
(c) A student needs 3.0 g of potassium nitrate. The student has a solution of potassium nitrate with a concentration of 60 g/dm3. Calculate the volume of solution, in cm3, that contains 3.0 g of potassium nitrate.[2]
Show the answer and mark scheme
(a)Answer: 20 g/dm3
250 cm3 = 0.25 dm3
5.0 ÷ 0.25 = 20 (g/dm3)
(b)Answer: 1.0 g
40 × 0.0250
1.0 (g)
(c)Answer: 50 cm3
3.0 ÷ 60 = 0.05 (dm3)
50 (cm3)
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