Question 1 Medium
Three results are 12.1, 12.3 and 12.2 cm³. Calculate the mean.
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Answer: 12.2 cm³
- Add them: 12.1 + 12.3 + 12.2 = 36.6.
- 36.6 ÷ 3 = 12.2 cm³.
Maths skills for chemistry: GCSE Combined Science Chemistry practice questions
A second set of questions on maths skills for chemistry. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
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Question 2 Medium
In 2H₂ + O₂ → 2H₂O, how many moles of O₂ react with 6 moles of H₂?
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Answer: 3
- The ratio of H₂ to O₂ is 2 : 1.
- 6 ÷ 2 = 3 mol of O₂.
Question 3 Hard
Calculate the percentage by mass of magnesium in magnesium oxide, MgO. Ar: Mg = 24, O = 16.
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Answer: 60%
- Mr of MgO = 24 + 16 = 40.
- 24 ÷ 40 × 100 = 60%.
Question 4 Hard
A line on a graph of gas volume against time rises from 10 cm³ at 5 s to 70 cm³ at 35 s. Calculate the gradient in cm³/s.
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Answer: 2.0 cm³/s
- Gradient = change in volume ÷ change in time.
- (70 − 10) ÷ (35 − 5) = 2.0 cm³/s.
Question 5 Hard
Convert 0.25 dm³ to cm³.
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Answer: 250
- Multiply by 1000.
- 0.25 × 1000 = 250 cm³.
Question 6 Hard
An atom has a radius of 1 × 10⁻¹⁰ m. A nanometre is 1 × 10⁻⁹ m. Give the radius in nm.
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Answer: 0.1 nm
- Divide the radius by the size of a nanometre.
- 1 × 10⁻¹⁰ ÷ 1 × 10⁻⁹ = 0.1 nm.
Question 7 Hard
Calculate the percentage by mass of calcium in calcium carbonate, CaCO₃. Ar: Ca = 40, C = 12, O = 16.
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Answer: 40%
- Mr of CaCO₃ = 40 + 12 + 48 = 100.
- 40 ÷ 100 × 100 = 40%.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is standard form?
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A × 10ⁿ, where A is between 1 and 10 and n is a whole number.
Check 2
What is 3 500 000 in standard form?
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3.5 × 10⁶.
Check 3
What is 0.00072 in standard form?
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7.2 × 10⁻⁴.
Check 4
How many cm³ are in 1 dm³?
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1000 cm³.
Check 5
How do you change cm³ to dm³?
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Divide by 1000.
Check 6
How do you change g to kg?
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Divide by 1000.
Check 7
How many mg are in 1 g?
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1000 mg.
Check 8
How many nm are in 1 m?
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1 × 10⁹ (a nanometre is 1 × 10⁻⁹ m).
Check 9
What is the radius of an atom, roughly?
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About 0.1 nm (1 × 10⁻¹⁰ m).
Check 10
What is 3.4567 to 2 decimal places?
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3.46.
Check 11
What is 0.004568 to 2 significant figures?
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0.0046.
Check 12
When should you round in a calculation?
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At the end, not part way through.
Check 13
What is the formula for concentration?
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Concentration = mass ÷ volume.
Check 14
What is the formula for moles?
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Moles = mass ÷ Mr.
Check 15
What is the formula for percentage by mass of an element?
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Ar × number of atoms ÷ Mr × 100.
Check 16
What does the ratio of H₂ to O₂ in 2H₂ + O₂ → 2H₂O tell you?
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2 : 1, so twice as many moles of hydrogen as oxygen react.
Check 17
What is the gradient of a line?
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Change in y divided by change in x.
Check 18
How do you find the rate at one moment from a curved graph?
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Draw a tangent to the curve and find its gradient.
Check 19
Which axis does the independent variable go on?
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The x-axis.
Check 20
What does a steeper line on a volume against time graph mean?
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A faster reaction.
Check 21
What does a flat line on a volume against time graph mean?
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The reaction has stopped.
Check 22
Why should you estimate an answer first?
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To check that your final answer is about the right size.
Check 23
What is the Avogadro constant?
Show answer
6.02 × 10²³ per mole.
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