This set has ten original questions that move between Biology, Chemistry and Physics, with no topic labels. They run from easier to harder and carry no mark labels. Check your own syllabus before treating any idea as in scope.
Use paper, write full sentences for explanations, and open each answer only after you have tried. The original mixed-practice builder can assemble longer printable sessions from reviewed questions.
The questions
1. A sealed syringe contains a gas. Explain, using particles, why the gas fills the whole syringe.
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The gas particles move randomly and quickly, and there are large gaps between them with very weak forces holding them together. They spread out until they fill the whole space available, so the gas has no fixed shape or volume.
The key word to name first is particles. Writing “the gas expands” with no mention of particle movement leaves the explanation incomplete.
2. A reaction gives off 36 cm³ of gas in 4 minutes at a steady rate. Calculate the rate.
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Rate = amount ÷ time = 36 ÷ 4 = 9 cm³ per minute.
Check: 9 × 4 = 36. The unit should contain “per minute”, because a rate is an amount per unit of time.
3. A cyclist travels 450 m in 1 minute 30 seconds. Calculate the average speed in m/s.
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Convert the time first: 1 minute 30 seconds = 90 s.
Speed = distance ÷ time = 450 ÷ 90 = 5 m/s.
Check: 5 × 90 = 450. Leaving the time as 1.5 and dividing would give 300, which is speed in metres per minute, not per second.
4. 2.4 g of magnesium burns in air and forms 4.0 g of magnesium oxide. Calculate the mass of oxygen that combined with the magnesium, and explain why the solid gained mass.
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Mass of oxygen = 4.0 − 2.4 = 1.6 g.
The product contains the magnesium plus oxygen taken from the air. Mass is conserved overall, so the extra mass in the solid came from the gas that joined it.
5. A 60 W lamp is switched on for 5 minutes. Calculate the energy transferred in joules, using energy = power × time.
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Convert the time: 5 minutes = 300 s.
Energy = 60 × 300 = 18 000 J.
Check: 60 × 300 = 60 × 3 × 100 = 180 × 100 = 18 000. Using 5 instead of 300 is the common slip, and it gives only 300 J.
6. Solution X turns red litmus paper blue. Write one observation and one inference.
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Observation: red litmus paper turned blue in solution X.
Inference: solution X is alkaline.
The observation is what you saw. The inference is the conclusion you drew from it, and it goes beyond the observation.
7. Five seedlings of the same age were measured after four weeks: 12, 13, 12, 25 and 14 cm. Identify the anomaly. Calculate the mean with and without it, and say what you would do next.
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The anomaly is 25 cm.
With all five: 12 + 13 + 12 + 25 + 14 = 76, so 76 ÷ 5 = 15.2 cm.
Without 25 cm: 12 + 13 + 12 + 14 = 51, so 51 ÷ 4 = 12.75 cm.
Do not delete the value simply because it is awkward. Check for a recording error or a difference in that seedling, such as a different position, and repeat the measurement if possible. State clearly which mean you report and why.
8. Grass is eaten by rabbits, and rabbits are eaten by foxes. A disease kills many rabbits. Predict what may happen to the grass and to the foxes in the short term, and give one reason your prediction might not hold.
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The grass may increase, because fewer rabbits eat it. The fox population may fall, because there is less food.
The prediction might not hold if foxes can eat other food, such as birds or insects, or if another animal begins to eat the grass. A prediction from a food web states what is likely, not what is certain.
9. A mixture of sand and salt dissolved in water is separated into dry sand and solid salt. Describe a method and say why it works.
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Filter the mixture. The sand does not dissolve, so it stays on the filter paper, while the salt solution passes through. Rinse and dry the sand.
Evaporate the water from the filtrate. The water leaves as vapour and the dissolved salt remains as a solid.
The method works because the two solids differ in solubility. Do not heat strongly if the salt starts to spit, and keep any practical work supervised.
10. A balance always reads 0.3 g too high. A student weighs a sample three times and gets 5.3 g, 5.3 g and 5.3 g. Does repeating the reading fix the problem? What is the likely true mass, and how would you improve the method?
Show answer
No. The three readings agree, so they are precise, but they are all shifted by the same error, so they are not accurate. Repeating a biased reading does not remove the bias.
If the error is known to be +0.3 g, the likely true mass is 5.3 − 0.3 = 5.0 g.
To improve the method, check the zero reading with nothing on the pan, or calibrate the balance, or test it against a known mass. Then weigh again.
If you got these wrong
| What went wrong | Go to |
|---|---|
| Explaining gas behaviour in particle terms (Q1) | particle model lesson |
| Rate and speed, including units (Q2, Q3) | graph to rate calculation |
| Mass change in a reaction (Q4) | equation with a supplied mass change |
| Energy and power (Q5) | circuit observation and energy transfer |
| Observation versus inference (Q6) | two chemical tests |
| Anomalies and means (Q7) | explaining an anomaly |
| Food web predictions (Q8) | food-web change |
| Separating a mixture (Q9) | separation sequence |
| Precision and accuracy (Q10) | repeated readings and bias |
If you cannot tell which science a question belongs to before you start, read the help page on changing models in mixed practice. Record each error in your mistake log.
Using the set well
Mark yourself on reasoning first and the final value second. A right answer reached by a lucky guess counts as a gap.
If one lesson keeps appearing, return to the learning guide. Where an explanation stops halfway, online one-to-one Combined Science tuition is the place to practise finishing it with a teacher listening.