How to label diagrams correctly in SPM Chemistry

You can draw a perfect apparatus set-up and still lose most of the marks, because in SPM Chemistry, the marks live in the labels, not the drawing. A neat, unlabelled diagram tells the examiner very little; a rougher one, labelled precisely, scores. Labelling is its own skill, and it appears on more than just apparatus questions: graphs, energy level diagrams, electron arrangement diagrams and electrolysis cells all carry label marks. This post covers how to label each of them the way the examiner expects.

The golden rules of a label

Whatever you are labelling, four rules always apply.

• The label line must touch the exact part it names. A line that stops in mid-air, or points near the wrong item, may not score. Use a ruler and end the line precisely on the part.
• Name things specifically. “Dilute hydrochloric acid,” not “acid.” “Zinc granules,” not “solid.” “Carbon electrode,” not just “electrode.” Vague labels lose the mark that a precise one would have earned.
• Label the chemicals as well as the apparatus. A test tube labelled “test tube” but with its unnamed contents left blank has thrown away half the answer.
• Write horizontally and clearly, outside the diagram, with the line leading in. Labels crammed inside the drawing or written at an angle are easy to misread.

Labelling apparatus diagrams

For a set-up, collecting a gas, heating a solid, a titration, label every piece of apparatus and every substance in it. Name the vessel correctly (boiling tube, test tube, conical flask, gas jar, delivery tube, burette), and name what it contains. If gas is collected, label the gas and the collection method. You can see how the standard practicals are labelled on our experiments reference, which is worth studying precisely for the wording examiners accept.

Labelling graphs

Graphs are quietly generous with marks, and quietly cruel if you skip the labels.

• Label each axis with the quantity and its unit, using a solidus: “Volume of gas / cm³” on the vertical axis, “Time / s” on the horizontal. An axis with a bare word, or no unit, can cost a mark.
• Give the graph a heading if the question implies a comparison, and label each curve when you draw more than one, for example “Experiment 1: higher temperature” and “Experiment 2: lower temperature.”
• When you take a gradient, draw and label the tangent, and show the triangle you used. The label makes your method visible so it can be marked.

Labelling energy level diagrams

Energy level (energy profile) diagrams have a fixed set of labels the examiner looks for.

• The vertical axis is energy; label it.
• Mark the energy level of the reactants and the energy level of the products with horizontal lines, correctly positioned: for an exothermic reaction the products sit lower than the reactants, and for an endothermic reaction they sit higher.
• Label the enthalpy change, ΔH, with a vertical arrow between the reactant and product levels, pointing down and negative for exothermic, up and positive for endothermic.
• Label the activation energy as the rise from the reactant level up to the peak.

Get the relative heights right and the labels precise, and these diagrams are among the most reliable marks on the paper.

Labelling electron arrangement diagrams

For an atom or ion, draw the nucleus, then the shells, and label them properly.

• Write the number of protons and neutrons in the nucleus if asked, for example, a sodium atom has 11 protons.
• Place the correct number of electrons in each shell and state the arrangement, such as 2.8.1 for sodium. For an ion, show the changed number of electrons and, where useful, the charge, the sodium ion, Na⁺, is 2.8.
• Keep the shells clearly separated so the count in each is unambiguous.

Use our SPM periodic table to check proton numbers and electron arrangements while you practise, so the numbers you label are correct.

Labelling electrolysis cells

Electrolysis is a favourite for diagram-and-label questions, and a fixed set of labels scores.

• Label the electrolyte by name, for instance, dilute sulfuric acid or molten lead(II) bromide.
• Label the two electrodes and their material (usually carbon), and mark which is the anode (positive) and which is the cathode (negative), since in electrolysis the anode connects to the positive terminal of the supply.
• Show and label the d.c. power supply or battery in the circuit, leaving it out is a common lost mark.
• If asked, label the direction of electron flow in the external wires. Revise the products at each electrode on our electrolysis of aqueous solutions page so your labels match the chemistry.

A quick labelling checklist

Before you move on from any diagram, run through this:

1. Does every label line touch the exact part?
2. Is every chemical named specifically, not vaguely?
3. Are units on both graph axes?
4. For an energy diagram, are reactants, products, ΔH and activation energy all labelled, with the right relative heights?
5. For electrolysis, are the electrolyte, both electrodes, the anode/cathode identity and the power supply all labelled?

When labels keep costing marks

Labelling is easy to get almost right and lose marks anyway, the line that misses, the “acid” that should have been named. In our online one-to-one lessons, our experienced SPM Chemistry teachers mark your diagrams exactly as the examiner will, catch the label that would have been rejected, and drill the standard set-ups until precise labelling is a habit. Lessons run in English from RM50 an hour, with a paid one-hour trial. Label properly, and diagram questions become some of the most dependable marks you own.