IGCSE Chemistry examiner tips 2026: How to stop losing marks you already know
IGCSE Chemistry examiner tips focus on one key principle: Knowing the content is not enough, you must communicate it in the precise way the mark scheme rewards. High-scoring answers use correct command words, accurate chemical terminology, clear working in calculations, and a strict distinction between observations and conclusions. Students also need to check equations, state symbols, qualitative analysis results, and avoid adding contradictory points that can cancel correct marks.
This guide highlights the examiner-backed habits and common mistakes that can make a real difference across Cambridge IGCSE Chemistry 0620.
- IGCSE Chemistry examiner tips for avoiding lost marks
- What IGCSE Chemistry examiners expect from high-scoring answers
- Read every Chemistry question and command word carefully
- Use precise chemical terminology instead of vague language
- Distinguish observations from conclusions in practical questions
- Write complete and precise Chemistry definitions
- Show every important step in calculation questions
- Check chemical formulae, equations and state symbols
- Use collision theory precisely in rate of reaction answers
- Check valencies when drawing organic structures
- Learn qualitative analysis tests and observations accurately
- Avoid giving extra contradictory answers
- Use short, focused points for multi-mark answers
- What examiner reports reveal about common Chemistry mistakes
- Frequently asked questions
IGCSE Chemistry examiner tips for avoiding lost marks
The most important shift any IGCSE Chemistry [1] student can make is to stop thinking about the exam as a knowledge test alone. It is also a communication test. Examiners are not searching for your understanding. They are scanning your written response for specific words, structures, and logical sequences that match the mark scheme.
This means a student who writes a correct idea in imprecise language will lose the mark. A student who writes a concise, accurate point aligned with mark scheme language will gain it. That distinction alone determines whether a student achieves a Grade A or a Grade B.
>>> Read more: IGCSE Chemistry 0620 books 2026: Complete guide for students and teachers
What IGCSE Chemistry examiners expect from high-scoring answers
Cambridge International uses three assessment objectives for IGCSE Chemistry 0620. AO1 covers knowledge and understanding of facts, principles, and concepts. AO2 tests the ability to handle, apply, and evaluate information. AO3 assesses experimental skills and investigations.
High-scoring students demonstrate competence across all three assessment objectives, not just AO1. Examiners frequently note in Cambridge examiner feedback that students over-rely on memorised facts and struggle when questions require them to apply knowledge to unfamiliar contexts.
| Assessment Objective | Focus | Example Task |
|---|---|---|
| AO1 | Recall of facts and definitions | Define oxidation in terms of electron transfer |
| AO2 | Application and analysis | Explain why increasing temperature increases rate of reaction |
| AO3 | Practical and investigative skills | Identify an unknown ion from a set of test observations |
>>> Read more: IGCSE Chemistry Energy Changes: Exothermic vs Endothermic + Calculations A*
Read every Chemistry question and command word carefully
One critical detail often overlooked is the command word at the start of each question. Cambridge International publishes a defined glossary of command words, and each one signals a specific type of response.
“Describe” asks you to state what happens. “Explain” asks you to give a chemical reason. “Suggest” tells you there is no single textbook answer and that you should apply your existing chemistry knowledge to a new situation. Writing a description when an explanation is required will cost you every mark in the AO2 column.
| Command Word | What It Requires | Common Student Error |
|---|---|---|
| Describe | State observable facts or steps | Giving reasons instead of observations |
| Explain | Give the chemical reason or mechanism | Describing without linking to theory |
| Suggest | Apply knowledge to unfamiliar context | Searching for a memorised answer |
| Deduce | Reach a logical conclusion from data | Guessing without showing reasoning |
| Calculate | Show working and give a numerical answer with units | Giving only the final number |
>>> Read more: IGCSE Chemistry Moles and Concentration 2026: A Clear Guide to Solving Common Exam Questions
Use precise chemical terminology instead of vague language
A common mistake we see at Times Edu is students substituting precise chemical vocabulary with everyday language. Phrases like “it reacts,” “things move around,” or “the solution goes clear” are not acceptable in Cambridge IGCSE Chemistry answers.
When a coloured solution becomes colourless, write “colourless,” not “clear.” When referring to particles, specify whether you mean atoms, ions, or molecules. Vague language signals to the examiner that the student does not fully understand the concept, even when they do.
Avoid using “element” when you mean “compound” and avoid using “they” or “it” without a clear chemical referent. Every pronoun in a Chemistry answer should have an obvious and specific noun attached to it.
>>> Read more: IGCSE Chemistry Mark Scheme Keywords for 2026: The Terms You Need to Use for Better Marks
Distinguish observations from conclusions in practical questions
This is one of the most consistent sources of lost marks across all IGCSE Chemistry examiner reports. Students mix up what they see with what it means, and in doing so, they fail to answer the question that was actually asked.
An observation is something you can perceive directly in a practical. A conclusion is the chemical interpretation of that observation. If a question asks “what do you observe when dilute hydrochloric acid is added to sodium carbonate,” the observation is “effervescence occurs” or “bubbles of gas are produced.” Saying “carbon dioxide is produced” is a conclusion, not an observation.
In our experience working with international students, separating these two types of thinking before writing an answer takes practice but becomes instinctive with proper drilling using past papers.
>>> Read more: IGCSE Chemistry 0620 Command Words: Decode Exam Questions for A*
Write complete and precise Chemistry definitions
Definitions in IGCSE Chemistry are marked with very little flexibility. Examiners are trained to look for key qualifying phrases, and missing even one word can cost the mark.
Take the definition of an exothermic reaction: It is a reaction that releases heat energy to the surroundings, causing the temperature of the surroundings to rise. Students who write “a reaction that releases energy” lose the mark because they omit the reference to surroundings or the temperature change.
Below are some definitions where precision is critical:
- Oxidation: The loss of electrons (or gain of oxygen).
- Reduction: The gain of electrons (or loss of oxygen). OIL RIG is the mnemonic: Oxidation Is Loss, Reduction Is Gain.
- Anode: The positive electrode. PANIC is the mnemonic: Positive Anode, Negative Is Cathode.
- Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons.
- Electrolysis: The decomposition of an ionic compound, in the molten state or in aqueous solution, by the passage of electricity.
>>> Read more: IGCSE Chemistry 0620 Topic Order: Best Sequence for A* Revision
Show every important step in calculation questions
Drawing on years of experience at Times Edu reviewing student scripts, we have seen students lose full marks on calculations by presenting only the final answer. Cambridge mark schemes award method marks as well as accuracy marks. If your final answer is wrong but your working is correct, you can still gain partial credit.
Every calculation answer should include: The formula or equation used, the substitution of values with units, the intermediate steps, and the final answer with correct units. Do not round intermediate values. Only round at the final step, and check whether the question specifies the number of significant figures or decimal places required.
A typical calculation for moles, for example, should look like this:
Moles = mass / molar mass
Moles = 4.0 g / 40 g/mol
Moles = 0.1 mol
This format makes it easy for the examiner to follow your reasoning and award marks even if a numerical slip occurs.
>>> Read more: IGCSE Chemistry Past Paper Strategy for 2026: Smart Ways to Practice for Better Results
Check chemical formulae, equations and state symbols
Balanced equations are a straightforward source of marks that students frequently give away. The most common errors include: Incorrect formulae for common substances, unbalanced equations, missing or incorrect state symbols, and failure to write ionic equations when specifically requested.
State symbols are (s), (l), (g), and (aq). They must be correct, not just present. Writing (aq) for a solid reactant because you remember that state symbols are required is worse than omitting them entirely, because it suggests a misunderstanding of the physical state of the substance.
For ionic equations, students must cancel spectator ions from both sides. A full equation that simply has the ionic formula substituted in is not an ionic equation. The net ionic equation must show only the species that actually participate in the reaction.
Use collision theory precisely in rate of reaction answers
Rate of reaction questions are a high-frequency topic in Cambridge IGCSE Chemistry 0620 past papers, and they require a very specific sequence of logic. Collision theory must be applied with precision, not stated as a vague principle.
A full-credit answer explaining why increasing temperature increases the rate of reaction should include: Particles move faster, collisions occur more frequently, a higher proportion of collisions have energy equal to or greater than the activation energy, and therefore the rate increases. Omitting the activation energy reference will cost you the final mark on a three-mark question.
One critical detail often overlooked is the distinction between collision frequency and collision energy. Both must increase with temperature. Saying only “particles collide more often” is incomplete and will receive partial credit at best.
Check valencies when drawing organic structures
Displayed formula questions test whether a student can draw accurate structural representations of organic molecules. The most common error is drawing carbon with the wrong number of bonds.
Carbon always forms four bonds. Hydrogen always forms one bond. Oxygen forms two bonds. Nitrogen forms three bonds. If any atom in your displayed formula has the wrong number of bonds, you will lose the mark for that structure regardless of whether the connectivity is otherwise correct.
A common mistake we see is students drawing methane as CH4 in molecular formula but then giving carbon only three bonds in the displayed formula. Check every atom systematically before moving on.
Learn qualitative analysis tests and observations accurately
Qualitative analysis is a topic where marks are either full or zero. There is no partial credit for almost remembering a test. Examiners require the exact observation linked to the exact ion or gas.
| Test | Reagent | Positive Observation |
|---|---|---|
| Chloride ions | Silver nitrate solution (acidified) | White precipitate |
| Bromide ions | Silver nitrate solution (acidified) | Cream precipitate |
| Iodide ions | Silver nitrate solution (acidified) | Yellow precipitate |
| Sulfate ions | Barium chloride solution (acidified) | White precipitate |
| Ammonium ions | Sodium hydroxide solution (warm) | Pungent gas, turns damp red litmus blue |
| Iron(II) ions | Sodium hydroxide solution | Green precipitate |
| Iron(III) ions | Sodium hydroxide solution | Brown/red-brown precipitate |
| Carbon dioxide gas | Limewater | Turns limewater milky/cloudy |
| Hydrogen gas | Burning splint | Squeaky pop |
| Oxygen gas | Glowing splint | Relights glowing splint |
| Chlorine gas | Damp litmus paper | Bleaches litmus paper white |
Memorise this table exactly as written. The language used here mirrors the language accepted in Cambridge mark schemes.
Avoid giving extra contradictory answers
This is one of the most counterintuitive rules in IGCSE Chemistry examination technique: Writing more can lose you marks. If you write one correct answer and one incorrect answer in response to the same mark point, many Cambridge mark schemes instruct examiners to award zero for that point.
This policy, sometimes called the “contradiction rule,” is applied strictly in Chemistry because precise scientific reasoning matters. If you are unsure about a point, write your best answer and stop. Do not hedge by adding an alternative in the same sentence or bullet point.
In our experience working with international students, this habit often develops from classroom environments where showing multiple ideas is rewarded. In Cambridge examinations, it is penalised.
Use short, focused points for multi-mark answers
When a question is worth three or four marks and asks you to “describe and explain,” treat it as a structured list rather than a paragraph. Each mark point corresponds to one distinct piece of information.
Write “what happens” first (the observation or change), then “why it happens” (the chemical reason). Keep each point to one or two sentences. Do not repeat yourself. Do not use transition phrases to pad answers.
A structured answer is easier for the examiner to mark, ensures you do not accidentally merge two separate mark points into one, and reduces the risk of contradiction errors.
What examiner reports reveal about common Chemistry mistakes
Cambridge International publishes Chief Examiner Reports after each examination series for IGCSE Chemistry 0620. These reports are among the most valuable and least-used resources available to students and teachers.
Drawing on years of experience at Times Edu reviewing these reports alongside student scripts, we have identified three recurring themes across multiple examination years. First, students lose marks on practical questions by stating conclusions instead of observations. Second, students write vague or incomplete definitions that miss the qualifying language required by the mark scheme. Third, students do not apply collision theory with enough specificity in rate of reaction questions.
Reading at least the last three years of examiner reports before your examination series is one of the highest-return preparation strategies available. It is not a substitute for past paper practice, but it tells you exactly where other students have failed and where examiners are paying close attention.
Frequently asked questions
What do examiners look for in IGCSE Chemistry answers?
Examiners look for precise chemical terminology, logical sequencing of ideas, correct use of command words, and answers that match the language and structure expected by the Cambridge mark scheme. They are not rewarding length or effort, only accuracy and relevance.
What are the most common mistakes in IGCSE Chemistry?
The most common mistakes include using vague language, confusing observations with conclusions, writing incomplete definitions, missing state symbols or units in calculations, and applying collision theory without reference to activation energy.
How precise do Chemistry answers need to be?
Very precise. Cambridge mark schemes typically accept a narrow range of accepted wording for each mark point. Using synonyms that are chemically imprecise, such as “clear” instead of “colourless,” will cost the mark. Use the exact language from your syllabus and past paper mark schemes.
Can you lose marks for writing too much in IGCSE Chemistry?
Yes. If you write a correct answer and an incorrect statement for the same mark point, the contradiction rule means you receive zero for that point. Write your best answer and stop.
Do you need state symbols in IGCSE Chemistry equations?
State symbols are required when the question asks for a complete or full equation and when the mark scheme specifically awards a mark for them. Check the question carefully. When in doubt, include them correctly rather than omitting them.
What is the difference between an observation and a conclusion in Chemistry?
An observation is something you can perceive directly during a practical, such as “a white precipitate forms” or “bubbles of gas are produced.” A conclusion is the chemical interpretation, such as “chloride ions are present” or “the gas is hydrogen.” Questions using the word “observe” require observations only.
How can I write answers that match the IGCSE Chemistry mark scheme?
Practice past papers under timed conditions, then compare your answers line by line against the published mark scheme. Identify the words and phrases you omitted. Over time, your written responses will begin to mirror the language that Cambridge examiners reward.
