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Percentage and Science Worksheet

KS3 / GCSEScience20 questions

Free to print and use in your classroom. No sign-up required.

Key formulas

Percentage error = (|approximate value − exact value| ÷ exact value) × 100

Percentage yield = (actual yield ÷ theoretical yield) × 100

Percentage composition = (mass of component ÷ total mass) × 100

Answer each question using the correct formula. Show your working clearly. Give answers to 1 decimal place where required.

  1. 1. A mixture contains 18 g of salt dissolved in 150 g of solution. What is the percentage concentration of salt in the solution?

  2. 2. A sample of rock contains 36 g of iron ore in a 240 g sample. What percentage of the rock is iron ore?

  3. 3. A chemistry student predicted they would produce 8.0 g of copper sulfate in a reaction but only obtained 6.4 g. Calculate the percentage yield.

  4. 4. A student measured the boiling point of water as 98.5 °C. The accepted value is 100.0 °C. Calculate the percentage error.

  5. 5. A student measured the density of aluminium as 2.85 g/cm³. The accepted value is 2.70 g/cm³. Calculate the percentage error to 1 decimal place.

  6. 6. A fertiliser contains 24 g of nitrogen in a 80 g bag. What percentage of the fertiliser is nitrogen?

  7. 7. In a biology survey, 340 out of 500 plants in a field were of species A. What percentage of the plants were species A?

  8. 8. A reaction was expected to produce 12.5 g of precipitate. The actual yield was 9.75 g. Calculate the percentage yield.

  9. 9. Air is approximately 78% nitrogen, 21% oxygen, and 1% other gases. In a 500 cm³ sample of air, what volume is nitrogen?

  10. 10. A student recorded the speed of sound as 355 m/s. The accepted value is 343 m/s. Calculate the percentage error to 1 decimal place.

  11. 11. A woodland habitat contained 120 oak trees and 80 birch trees. What percentage of the trees were oak?

  12. 12. A chemistry experiment produced 14.4 g of magnesium oxide. The theoretical yield was 16.0 g. Calculate the percentage yield.

  13. 13. A 250 g alloy contains 175 g of iron and 75 g of carbon. What percentage of the alloy is carbon?

  14. 14. A student estimated the acceleration due to gravity as 9.4 m/s². The accepted value is 9.8 m/s². Calculate the percentage error to 1 decimal place.

  15. 15. In a population study, 1,350 out of 1,800 individuals in a sample carried a particular gene. What percentage carried the gene?

  16. 16. A solar panel converts 18% of light energy into electrical energy. If it receives 2,500 J of light energy, how many joules of electrical energy does it produce?

  17. 17. A chemical reaction was 85% efficient. If the theoretical yield was 40 g, what mass of product was actually obtained?

  18. 18. A student measured the melting point of a substance as 52.8 °C. The true value is 55.0 °C. Calculate the percentage error to 1 decimal place.

  19. 19. A 200 cm³ seawater sample contains 7 cm³ of dissolved salt (by volume). What is the percentage concentration of salt?

  20. 20. In a genetics experiment, out of 480 offspring, 360 showed the dominant trait. What percentage showed the dominant trait? How does this compare to the expected 75%?

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Worked Answers

  1. 1. 12%

    18 ÷ 150 × 100 = 12%.

  2. 2. 15%

    36 ÷ 240 × 100 = 15%.

  3. 3. 80%

    Percentage yield = 6.4 ÷ 8.0 × 100 = 80%.

  4. 4. 1.5%

    |98.5 − 100.0| = 1.5. Percentage error = 1.5 ÷ 100.0 × 100 = 1.5%.

  5. 5. 5.6%

    |2.85 − 2.70| = 0.15. Percentage error = 0.15 ÷ 2.70 × 100 = 5.555... = 5.6% (1 d.p.).

  6. 6. 30%

    24 ÷ 80 × 100 = 30%.

  7. 7. 68%

    340 ÷ 500 × 100 = 68%.

  8. 8. 78%

    Percentage yield = 9.75 ÷ 12.5 × 100 = 78%.

  9. 9. 390 cm³

    78% of 500 = 0.78 × 500 = 390 cm³.

  10. 10. 3.5%

    |355 − 343| = 12. Percentage error = 12 ÷ 343 × 100 = 3.499... = 3.5% (1 d.p.).

  11. 11. 60%

    Total trees = 120 + 80 = 200. Oak: 120 ÷ 200 × 100 = 60%.

  12. 12. 90%

    Percentage yield = 14.4 ÷ 16.0 × 100 = 90%.

  13. 13. 30%

    75 ÷ 250 × 100 = 30%.

  14. 14. 4.1%

    |9.4 − 9.8| = 0.4. Percentage error = 0.4 ÷ 9.8 × 100 = 4.081... = 4.1% (1 d.p.).

  15. 15. 75%

    1,350 ÷ 1,800 × 100 = 75%.

  16. 16. 450 J

    18% of 2,500 = 0.18 × 2,500 = 450 J.

  17. 17. 34 g

    85% of 40 = 0.85 × 40 = 34 g.

  18. 18. 4.0%

    |52.8 − 55.0| = 2.2. Percentage error = 2.2 ÷ 55.0 × 100 = 4.0%.

  19. 19. 3.5%

    7 ÷ 200 × 100 = 3.5%.

  20. 20. 75%; this matches the expected 75% exactly.

    360 ÷ 480 × 100 = 75%. The experimental result matches the expected Mendelian ratio of 3:1 (75% dominant) perfectly in this case.

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