How to draw diagrams that earn marks in SPM Chemistry

Diagram marks in SPM Chemistry are among the most winnable on the paper, because there is a right way to draw apparatus and it can be learned in an afternoon. Yet they are also quietly lost, an unlabelled test tube, a gap where a tube should meet a stopper, a beaker drawn where a boiling tube was needed. This post is about drawing the apparatus set-ups the exam asks for in a way that collects every available mark.

Draw a clean two-dimensional cross-section

SPM apparatus diagrams are drawn as simple two-dimensional cross-sections, not artistic 3-D pictures. Use a pencil and a ruler for straight edges such as tube walls and the sides of a beaker. Draw the apparatus large enough to label clearly, a tiny sketch crammed into a corner costs you marks because the examiner cannot see what each part is. Keep the outline single-lined and clean; you are drawing a working diagram, not a still life.

Label every important part, with lines that touch

Labels are where diagram marks actually live. Each label should have a straight line ending exactly on the part it names. A few rules that examiners reward:

• Label the apparatus (test tube, boiling tube, delivery tube, gas jar, beaker, conical flask, thermometer) and the chemicals in it.
• Name substances properly, “dilute hydrochloric acid”, “zinc granules”, “limewater”, not vague words like “acid” or “liquid”.
• Make the label line touch the exact part. A line that stops in mid-air, or points at the wrong item, may not score.

A correct set-up with no labels often earns only a fraction of the marks. Labelling is not decoration; it is half the answer.

Seal the apparatus: no gaps, no leaks

The most common diagram error is leaving a gap where two pieces of apparatus must connect. If you are collecting a gas, the delivery tube must be shown sealed into the stopper, and the stopper sealed into the mouth of the tube, with no gap through which gas would escape. An open join tells the examiner the gas would leak, and the mark is lost. Before you finish, trace the gas path with your pencil tip and check it is closed from the reaction vessel all the way to where the gas is collected.

Choose the right apparatus for the job

Drawing the wrong vessel is an easy slip. A boiling tube is larger and made for heating; a test tube is smaller and for observing. If a question involves heating a solid strongly, draw a boiling tube, not a thin test tube. For measuring an exact volume of solution you draw a burette or a pipette, not a measuring cylinder. Matching the apparatus to the task is itself part of what the diagram mark is testing.

Know the standard set-ups cold

A handful of set-ups recur, and knowing each one means you can reproduce it under pressure:

• Collecting a gas over water, a delivery tube leads under an inverted gas jar or measuring cylinder filled with water, used for gases only slightly soluble in water, such as hydrogen or oxygen.
• Downward delivery (upward for the tube), for a gas denser than air, such as carbon dioxide, the delivery tube points down into an upright gas jar; for a gas less dense than air, the jar is inverted.
• Collecting gas in a syringe, used when you need to measure the volume of gas produced over time, as in a rate-of-reaction experiment.
• Heating with a Bunsen burner, show the burner beneath the apparatus, and place a thermometer with its bulb in the liquid, not resting on the glass, when temperature is measured.

You can see many of these set-ups in context on our experiments hub, which walks through the standard SPM practicals apparatus and all.

The electrolysis cell, drawn properly

Electrolysis is a favourite for diagram questions. A complete cell shows: the electrolyte in a container, two electrodes (carbon or the named metal) dipping into it, each electrode connected by wire to a battery or d.c. power supply, and the electrodes labelled anode (positive) and cathode (negative). Label the electrolyte by name. Leaving out the battery, or failing to label which electrode is which, are the usual ways marks slip away here. This connects directly to the redox chemistry you can revise in our redox and electrolysis chapter.

A final checklist before you move on

When your diagram is done, run through five quick checks:

1. Is it a clean, ruled, two-dimensional cross-section, drawn large enough to read?
2. Is every apparatus part and every chemical labelled, with lines that touch?
3. Are all joins sealed, so no gas could leak?
4. Is it the correct apparatus for the task?
5. For a gas or electrolysis question, is the collection method or the full circuit shown?

Diagram questions appear in written papers and matter again in the practical Paper 3, so the habit pays twice. If you would like a teacher to check your diagrams and drill the standard set-ups with you, our online one-to-one lessons run in English from RM50 an hour, with a paid one-hour trial, our experienced SPM Chemistry teachers and our team mark diagrams exactly the way the examiner will, so nothing easy is left on the table.