These eleven questions cover variables, tables, apparatus, anomalous readings and improvements. All data are invented for practice. Nothing here is a procedure to carry out.
Try each question on paper, then open the answer and compare your reasoning, not only your final number. The skills come from practical-data interpretation, and you can record slips in the mistake log.
Questions
1. (Variables) Students investigate how the mass of manganese(IV) oxide catalyst affects the volume of gas collected from hydrogen peroxide solution in 60 s. Name the independent variable, the dependent variable and two control variables.
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- Independent: mass of catalyst / g.
- Dependent: volume of gas collected in 60 s / cm³.
- Controls (any two): volume of hydrogen peroxide solution, concentration of hydrogen peroxide solution, starting temperature, time allowed (60 s).
2. (Variables) A class investigates how the surface area of marble chips affects the speed at which they react with dilute acid. Which is the dependent variable: surface area, mass of marble or speed of reaction?
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Speed of reaction (measured, for example, as time or gas volume). Surface area is the independent variable, and the mass of marble should be kept fixed as a control.
3. (Tables) A student writes the heading “Time” and the cells “58 s”, “41 s” and “29 s”. Rewrite the heading and the cells correctly.
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Heading: Time / s. Cells: 58, 41, 29.
4. (Tables and means) Complete the mean column.
| Mass of catalyst / g | Volume 1 / cm³ | Volume 2 / cm³ | Mean volume / cm³ |
|---|---|---|---|
| 0.1 | 18 | 20 | |
| 0.2 | 35 | 37 | |
| 0.3 | 52 | 52 |
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- 0.1 g: (18 + 20) ÷ 2 = 38 ÷ 2 = 19
- 0.2 g: (35 + 37) ÷ 2 = 72 ÷ 2 = 36
- 0.3 g: (52 + 52) ÷ 2 = 104 ÷ 2 = 52
5. (Apparatus) A diagram shows a flask connected by a delivery tube to a gas syringe. State what is measured, and explain one way the measured value could be lower than the true value.
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The volume of gas produced, in cm³, is measured by the syringe. It could be lower if some gas escapes before it reaches the syringe, for example through a loose connection or before the flask is sealed.
6. (Apparatus reasoning) A student wants to collect ammonia by displacing water, as is done for hydrogen. Explain why this is unsuitable.
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Ammonia is very soluble in water, so it would dissolve in the water rather than collecting as a gas, and the volume measured would be wrong. Hydrogen is only slightly soluble, which is why collection over water suits it.
7. (Anomalous reading) Four repeat times were 52 s, 50 s, 66 s and 51 s. Identify the anomalous reading, suggest one cause, and calculate the mean of the others.
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66 s is anomalous because it is far from the other three. One possible cause is that the timer was stopped late. Mean: (52 + 50 + 51) ÷ 3 = 153 ÷ 3 = 51 s.
8. (Anomaly in a trend) Mean times were: 20 °C, 90 s; 30 °C, 58 s; 40 °C, 75 s; 50 °C, 22 s; 60 °C, 15 s. Which reading is anomalous, and what should be done?
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75 s at 40 °C breaks the pattern, because times should keep falling as temperature rises, yet this value is longer than the one at 30 °C. Repeat the test at 40 °C. If that is not possible, state that it is anomalous and leave it out when describing the trend.
9. (Improvement) A report states that some gas escaped before the bung was in place. Suggest one specific, safe conceptual improvement and its effect.
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Arrange the apparatus so that the system is fully connected and sealed before the reactants are combined. The effect is that less gas is lost, so the measured volume is closer to the true volume. No new hazard is introduced.
10. (Uncertainty) A measuring cylinder has an uncertainty of ±0.5 cm³. Calculate the percentage uncertainty for a reading of 20 cm³ and for a reading of 5 cm³. What does this suggest about the volume chosen?
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- 20 cm³: 0.5 ÷ 20 × 100 = 2.5%.
- 5 cm³: 0.5 ÷ 5 × 100 = 10%.
Measuring a larger volume gives a smaller percentage uncertainty, so it is better for precision.
11. (Mixed) Times for a reaction (invented): at 30 °C, 55 s, 57 s and 56 s; at 50 °C, 22 s, 21 s and 41 s. Identify any anomalous reading, find both means and state the pattern.
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- 30 °C: (55 + 57 + 56) ÷ 3 = 168 ÷ 3 = 56 s.
- 50 °C: 41 s is anomalous, because it is far from 22 s and 21 s. Mean of the others: (22 + 21) ÷ 2 = 43 ÷ 2 = 21.5 s.
- Pattern: a higher temperature gave a shorter time. 56 ÷ 21.5 ≈ 2.6, so the time at 50 °C was about 2.6 times shorter.
If you got these wrong
- Questions 1 and 2: revisit selecting variables. Check that each variable is a quantity, not a substance, and that controls have a stated value.
- Questions 3 and 4: revisit drawing a results table with units. Check headings, units, and the order of columns.
- Questions 5 and 6: revisit reading an apparatus diagram. Link each part to a purpose and each method to a property such as solubility.
- Questions 7, 8 and 11: revisit identifying an anomalous reading. Compare repeats, check the trend, then recalculate.
- Questions 9 and 10: revisit proposing a safe conceptual improvement. Name the limitation, the change and the effect.
Content topics that feed these questions include rates of reaction. If amounts of substance appear, the mole and equation-ratio tutor helps with the chemistry separately from the practical reading.
If several errors fall in one group, that pattern matters more than the individual marks. It is exactly what a teacher in online one-to-one Chemistry tuition can help you find and fix.