How Examiners Mark IGCSE Chemistry Papers

Understanding how examiners mark your paper changes how you write your answers. Most students imagine the examiner reading their response as a narrative and forming an overall impression. The reality is very different. Examiners mark by points, using a rigid scheme, often scanning hundreds of scripts for the same question. Knowing this process helps you write answers that are easy for the examiner to mark — and therefore more likely to score full marks.

The marking process

How papers reach the examiner

After the exam, your paper is scanned and uploaded to a digital marking system. Examiners access the scripts online and mark specific questions, not whole papers. An examiner might mark question 4 across 300 scripts. This means they become extremely familiar with what the correct answer looks like and what common wrong answers look like.

How the mark scheme is applied

Before marking begins, Cambridge holds a standardisation meeting where senior examiners discuss the mark scheme and agree on how to apply it to various student responses. Additional “acceptable alternatives” may be added based on responses seen during this process. The finalised scheme is then used by all examiners.

For each mark point, the examiner looks for specific information:

1. Is the required scientific term present?
2. Is the statement scientifically accurate?
3. Does the answer address what the question asked?

If all three are met, the mark is awarded. If any one is missing, it is not.

What “error carried forward” means

If you make an error in part (a) and use that incorrect answer in part (b), the examiner applies “error carried forward” (ecf). This means they mark part (b) based on your incorrect value from part (a). If your method in part (b) is correct, you score the method marks even though your starting value was wrong. This is why showing working matters: it allows the examiner to follow your logic and award ecf marks.

What “ignore” and “reject” mean

The scheme sometimes marks specific statements as:

• Ignore: The statement is neither right nor wrong; it does not affect the mark either way.
• Reject (R): The statement is wrong, and if present alongside a correct statement, it may negate the correct mark. For example, if the correct answer is “ionic bonds are strong electrostatic forces between oppositely charged ions” and you also write “the atoms are held together,” the word “atoms” (instead of ions) may be rejected, cancelling your otherwise correct answer.

This is why concise answers are safer than long ones. Extra correct information does not earn extra marks, but extra incorrect information can lose marks.

What examiners look for in different question types

Definitions (1-2 marks)

The examiner matches your words against the scheme. Precision matters. “A catalyst speeds up a reaction” is too vague if the scheme requires “increases the rate of a chemical reaction without being used up.” The second clause (without being used up) is a separate mark point.

Observations (1-2 marks per observation)

The examiner looks for what you would see, hear, or smell — not what you would conclude. “Effervescence” or “bubbles of gas” is an observation. “Hydrogen is produced” is a conclusion. If the question asks for an observation, give the observation. If it asks for an observation and a conclusion, give both.

Colour changes must be specific: “blue to colourless” scores; “it changes colour” does not. State the starting colour and the final colour.

Explanations (2-4 marks)

The examiner reads for mark points, typically one per mark. A 3-mark explanation needs three distinct points. A long paragraph that makes two points beautifully still scores 2/3.

The structure the examiner appreciates:

• Point 1 (the factual statement)
• Point 2 (the causal link)
• Point 3 (the consequence or conclusion)

Example (3 marks): “Why does the rate of reaction increase when concentration increases?”

• More solute particles per unit volume [1]
• More frequent collisions between reactant particles [1]
• Therefore more successful collisions per unit time [1]

Calculations (2-4 marks)

The examiner awards marks for:

• Correct formula [1]
• Correct substitution [1]
• Correct answer with units [1]

If your answer is wrong but your formula and substitution are correct, you score 2/3. If you write only the final answer and it is wrong, you score 0/3. This is the strongest argument for showing all working.

Equations (1-2 marks)

Typically: correct formulae [1], correctly balanced [1]. An unbalanced equation with correct formulae scores 1/2. An equation with wrong formulae scores 0/2 even if it is “balanced.”

Diagrams (1-3 marks)

The examiner checks for: correct shape or arrangement [1], correct labels [1], correct proportions and additional detail [1]. A diagram without labels is like an answer without key terms — the examiner cannot tell whether you know what each part represents.

How to use this knowledge

Write for the mark scheme, not for the teacher

Your teacher appreciates detailed, discursive answers. The examiner appreciates clear, concise answers that hit the mark points. In an exam, write for the examiner:

• One distinct point per mark
• Use the scientific term the scheme expects
• Do not pad with background information the question did not ask for

Count your points against the marks

Before moving on from a question, count: “This question is worth 3 marks. I have made three distinct points.” If you have only two, you are leaving a mark behind.

Avoid contradictions

If you are not sure, say nothing rather than saying something wrong alongside something right. The wrong statement can cancel the right one. “The reaction is exothermic and absorbs energy” is contradictory and may score zero, whereas “the reaction is exothermic” alone would score the mark.

Use diagrams when they add clarity

Examiners appreciate well-labelled diagrams, particularly for apparatus, bonding, and energy level questions. A diagram can earn marks independently of your written answer. If the question does not ask for a diagram but one would help your explanation, include it — it cannot hurt and may earn additional marks or clarify a confusing written answer.

Write legibly

Examiners mark scripts on screen, and poor handwriting becomes harder to read when scanned. Chemical formulae with unclear subscripts (is that O2 or O2?) cost marks. If your handwriting is consistently messy, consider printing your answers. Speed matters, but not at the cost of legibility.

The examiner is not your enemy. They want to give you marks. They apply the scheme fairly, looking for the specific information that earns each mark point. Your job is to make it easy for them to find that information in your answer.