Lesson 1 of 8

Read unfamiliar data

Select evidence and connect it to a chemical principle.

O-Level 6092 (2026) / SEC G3 K324 (2027)

I can analyse, conclude and evaluate.Syllabus
Syllabus K324, ACE. Analyse, conclude and evaluate

Read unfamiliar data with a purpose

Separate the question, the evidence and the chemistry that connects them.

Start with the quantity or claim the question asks you to establish. Then locate the relevant measurements, conditions and any new definitions in the stem. An unfamiliar substance name does not make its data unusable: use the supplied information together with a familiar idea such as conservation of atoms, collision frequency or intermolecular attraction.

From information to an answer

Name the task
For a calculation, identify the required quantity and unit. For an explanation, identify the observation that needs explaining.
Select the evidence
Extract the relevant rows, axes and conditions. Distinguish a measurement from a proposed explanation; do not use every number just because it is present.
Connect a principle
State the chemical relationship that makes the evidence relevant. Check that the comparison holds other important variables constant.
State the result and its limit
Give a numerical answer with units, or a conclusion supported by a specific comparison. State an assumption where the inference depends on it.

Worked exampleAssess a claim about a catalyst

Two runs use the same amount of reactant and the same temperature. Run A gives 40 cm³ of gas in 20 s; run B gives 40 cm³ in 50 s. Both eventually give 60 cm³. A report says: "A produces more product because it is faster."

Try it first. Then show the worked stepsHide the worked steps

The time to reach the same volume is smaller for A: its average rate to 40 cm³ is 2.0 cm³ s^-1, compared with 0.80 cm³ s^-1 for B.
The final volumes are the same under the same collection conditions, so these data do not show more final gaseous product in A.
The evidence supports faster production, not a greater final amount. Identifying the cause as a catalyst also requires the stated experimental difference between the runs.

Answer

Compare rate using a time interval and final amount using the plateau. They answer different questions.

A useful explanation joins evidence and mechanism: "At the same temperature and reactant concentration, this catalyst gives a higher measured rate; it provides an alternative pathway with a lower activation energy." Merely repeating "the graph is higher" does not explain the chemistry.

Check your understanding

A table gives temperature, concentration, reaction time and the colour of the laboratory bench. Which data belong in an explanation of the rate trend?

Temperature, concentration and reaction time, after checking which one was changed
Every column, since the examiner put each one there to be used in the answer
Reaction time alone, since rate is calculated from time and nothing else

Show the answer

Temperature, concentration and reaction time, after checking which one was changed

Use the variables that can affect rate, and find out which one was varied. Bench colour has no chemical role, so do not invent a link just because a detail is given.

Exam-style question

Data-based question
Astronauts breathe out carbon dioxide. In a small spacecraft, the air is pumped through a canister of a solid metal hydroxide, which removes the carbon dioxide. The hydroxide reacts with carbon dioxide to form a metal carbonate and water. The reaction is fastest when a thin film of water covers the solid, because carbon dioxide dissolves in the film and reacts there. In very wet air, the solid can turn into a paste that blocks the air flow.
Engineers tested 1.00 kg of three hydroxides. Air at 25 °C with 60% humidity was pumped through each one until the canister stopped working. Relative atomic masses: H 1, Li 7, C 12, O 16, Na 23, Ca 40.
Table 1. Carbon dioxide removed by 1.00 kg of each hydroxide
hydroxide largest possible mass of CO₂ removed / g measured mass of CO₂ removed / g
lithium hydroxide, LiOH (you calculate this) 750
sodium hydroxide, NaOH 550 430
calcium hydroxide, Ca(OH)₂ 595 400
Table 2. Carbon dioxide removed by 1.00 kg of LiOH as the humidity of the air changes
humidity of the air / % 0 20 40 60 80
mass of CO₂ removed / g 210 520 700 750 690
(a) Write the balanced equation, with state symbols, for the reaction of lithium hydroxide with carbon dioxide. [2]
(b) Calculate the largest possible mass of carbon dioxide that 1.00 kg of lithium hydroxide can remove. [3]
(c) Calculate the measured mass for LiOH as a percentage of your answer to (b). [1]
(d) Every kilogram carried into space is costly. Use Table 1 to explain why spacecraft use lithium hydroxide rather than the other two hydroxides. [2]
(e) Use Table 2 and the information above to describe and explain how the humidity of the air affects the mass of carbon dioxide removed. [3]
[11]

Table 1. Carbon dioxide removed by 1.00 kg of each hydroxide
hydroxide	largest possible mass of CO₂ removed / g	measured mass of CO₂ removed / g
lithium hydroxide, LiOH	(you calculate this)	750
sodium hydroxide, NaOH	550	430
calcium hydroxide, Ca(OH)₂	595	400

Table 2. Carbon dioxide removed by 1.00 kg of LiOH as the humidity of the air changes
humidity of the air / %	0	20	40	60	80
mass of CO₂ removed / g	210	520	700	750	690

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