IGCSE Chemistry show your working 2026: The complete guide to calculation marks
In IGCSE Chemistry, showing your working means making every calculation step visible so the examiner can see how you reached your answer. Students should write the formula, substitute the values clearly, show intermediate results, and include the correct units rather than giving only a final number. This is especially important because Cambridge awards method marks and can apply error carried forward when the correct process is shown.
This guide explains how to present working clearly across mole, stoichiometry, concentration, gas volume, empirical formula, and percentage calculations in Cambridge IGCSE Chemistry 0620.
- IGCSE Chemistry show your working rules for calculations
- Do you need to show your working in IGCSE Chemistry?
- What does show your working mean in a Chemistry question?
- When Cambridge specifically requires working to be shown
- Why showing calculation steps is good exam practice
- How to structure working in mole calculations
- How to show working in stoichiometry questions
- How to show working in concentration calculations
- How to show working in gas volume calculations
- How to show working in empirical formula questions
- How to show working in percentage yield and purity questions
- How to include formulas, substitution and final answers
- When to include units in your calculation
- Why you should avoid rounding intermediate answers
- How mark schemes treat correct answers without working
- Common mistakes when showing Chemistry working
- Frequently asked questions
IGCSE Chemistry show your working rules for calculations
Cambridge International sets clear expectations for how students should present numerical work. The core rule is simple: Every step that transforms one value into another must be visible on the page.
This includes writing the formula you are using, substituting the raw numbers into that formula, and stating the result of each individual step before moving to the next one. A bare final answer, even if numerically correct, gives the examiner nothing to work with if a marking check reveals an error.
>>> Read more: IGCSE Chemistry examiner reports 2026: What every student must know before their exam
Do you need to show your working in IGCSE Chemistry?
Technically, Cambridge does not always use the exact phrase “show your working” in every calculation question. What the mark scheme does instead is allocate marks to individual steps, and those marks can only be awarded if the examiner can see the step was performed.
In our experience working with international students across multiple exam cycles, students who write only a final answer either receive full marks or zero. There is no middle ground. Students who show step-by-step working, on the other hand, almost always recover at least partial credit even when their final answer is wrong.
The practical answer is yes: Always show your working, regardless of whether the question explicitly tells you to.
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What does show your working mean in a Chemistry question?
Showing your working in an IGCSE Chemistry [1] question means writing out three things in sequence: The formula or relationship you are applying, the substitution of actual numbers into that formula, and the numerical result of that step.
It does not mean writing a paragraph of explanation. It means a structured, vertical sequence of mathematical statements, each labelled clearly so the examiner knows which substance or quantity each number refers to.
A common mistake we see is students writing a chain of operations horizontally across a single line, such as “11.2 / 56 = 0.2 x 160 = 32.” This style makes it nearly impossible for an examiner to identify which step corresponds to which mark, and method marks are routinely withheld as a result.
>>> Read more: IGCSE Chemistry exam technique 2026: The complete guide to scoring higher marks
When Cambridge specifically requires working to be shown
Cambridge mark schemes for IGCSE Chemistry 0620 use specific language to signal when working is being assessed. Phrases such as “allow full marks for correct answer only if working is shown” and “award 1 mark for correct method seen” are standard annotations in Paper 4 and Paper 6 mark schemes.
The term “method mark” refers to a mark awarded specifically for demonstrating a correct calculation procedure, even if the final answer that results from it is wrong. These marks exist precisely to reward students who understand the chemistry but make a arithmetic slip.
Drawing on years of experience at Times Edu reviewing Cambridge mark schemes, the pattern is consistent: Multi-step calculation questions allocate one mark per logical step, and each of those marks is only accessible through visible working.
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Why showing calculation steps is good exam practice
Beyond the mark scheme mechanics, there is a strategic reason to show your working: The Error Carried Forward principle, often abbreviated as ecf in Cambridge mark schemes. If you make an arithmetic mistake in Step 1 but correctly apply that wrong value through Steps 2 and 3, the examiner will award the method marks for Steps 2 and 3.
Without visible working, there is no evidence that you carried anything forward correctly. The examiner sees one wrong number and awards zero.
One critical detail often overlooked is that ecf protection only applies when the working is clear enough for the examiner to trace your logic. Messy, unlabelled numbers do not qualify, even if the sequence of operations is technically present.
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How to structure working in mole calculations
The N.M.R. Framework is the most reliable layout for mole-based calculations in IGCSE Chemistry. It organises your working into three labelled stages: Number of moles of the known substance, Molar ratio from the balanced equation, and Rearrange the formula for the unknown target.
Step 1: N, Number of moles of the known substance
Write the mole formula explicitly, then substitute the numbers given in the question.
Moles of Fe = Mass / Relative Atomic Mass (Ar)
Moles of Fe = 11.2 / 56 = 0.20 mol
Step 2: M, Molar ratio from the balanced equation
State the ratio as it appears in the balanced equation, then use it to calculate moles of the target substance.
Ratio of Fe2O3 : Fe = 1 : 2
Moles of Fe2O3 = 0.20 / 2 = 0.10 mol
Step 3: R, Rearrange for the target quantity
Calculate the relative formula mass (Mr) explicitly, then apply the rearranged mole formula.
Mr of Fe2O3 = (56 x 2) + (16 x 3) = 112 + 48 = 160 g/mol
Mass of Fe2O3 = Moles x Mr = 0.10 x 160 = 16.0 g
This layout makes every mark-earning step visible and labelled. Examiners can follow it in under ten seconds.
>>> Read more: IGCSE Chemistry Moles and Concentration 2026: A Clear Guide to Solving Common Exam Questions
How to show working in stoichiometry questions
Stoichiometry questions test whether you can use a balanced equation to relate the amounts of reactants and products. The working method is identical to the N.M.R. Structure, but you must always write the balanced equation first if it is not already provided, or copy it clearly from the question.
A common mistake we see is students skipping the ratio step and jumping directly from moles of one substance to mass of another. This collapses two marks into one step and risks losing the method mark for the ratio if the conversion factor is wrong.
Always write the ratio line explicitly, such as “mole ratio of HCl : Na2CO3 = 2 : 1,” before performing the division or multiplication. This single habit protects at least one method mark in virtually every stoichiometry question on Paper 4.
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How to show working in concentration calculations
Concentration calculations use the core relationship: Concentration (mol/dm3) = moles / volume (dm3). The most frequent error in this calculation type is forgetting to convert volume from cm3 to dm3 before substituting.
Show your unit conversion as a separate labelled step:
Volume = 25.0 cm3 = 25.0 / 1000 = 0.0250 dm3
Then write the formula, substitute, and solve:
Concentration = Moles / Volume = 0.00500 / 0.0250 = 0.200 mol/dm3
In our experience working with international students, those who convert units as a visible step almost never lose the unit-conversion mark, while those who convert mentally and skip writing it down lose it consistently.
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How to show working in gas volume calculations
At room temperature and pressure (rtp), one mole of any gas occupies 24 dm3 (or 24,000 cm3). Molar volume calculations require you to show the formula, the known molar volume constant, and the substitution clearly.
Volume of gas = Moles x Molar Volume
Volume of gas = 0.050 x 24 = 1.2 dm3
If the question asks you to work backwards from a gas volume to moles, rearrange the formula first in writing, then substitute. Showing the rearrangement step earns the method mark even if you subsequently make an arithmetic error.
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How to show working in empirical formula questions
Empirical formula questions require a structured table layout. Writing the steps as flowing prose or a horizontal chain causes marks to be lost when the examiner cannot trace which element corresponds to which value.
The recommended working layout for empirical formula questions is a column-based table:
| Step | Element C | Element H | Element O |
|---|---|---|---|
| % composition | 40.0 | 6.7 | 53.3 |
| Divide by Ar | 40.0/12 = 3.33 | 6.7/1 = 6.7 | 53.3/16 = 3.33 |
| Divide by smallest | 3.33/3.33 = 1 | 6.7/3.33 = 2 | 3.33/3.33 = 1 |
| Ratio | 1 | 2 | 1 |
Empirical formula: CH2O
This tabular format is explicitly recognised in Cambridge mark schemes. It makes every division step visible and keeps the working organised under pressure.
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How to show working in percentage yield and purity questions
Percentage yield requires you to show both the theoretical yield calculation and the percentage formula application as separate steps.
Step 1: Calculate theoretical yield using the N.M.R. Method (show full stoichiometric working).
Step 2: Apply the percentage yield formula explicitly:
Percentage yield = (Actual yield / Theoretical yield) x 100
Percentage yield = (8.5 / 10.0) x 100 = 85.0%
Percentage purity follows the same two-step logic but in reverse: The actual mass is the pure substance, and you are finding what fraction of the total sample it represents. One critical detail often overlooked is that percentage purity questions require you to state clearly which mass is the “pure” mass and which is the “total sample” mass before substituting.
How to include formulas, substitution and final answers
The standard three-line format for any Chemistry calculation step is: Formula line, substitution line, answer line. Never collapse these into one line. Each line earns marks independently.
Formula line: Moles = Mass / Mr
Substitution line: Moles = 8.0 / 40
Answer line: Moles = 0.20 mol
This structure means that even if your Mr value is wrong in the substitution line, the examiner can award the formula mark and possibly the method mark for the correct rearrangement, as long as the structure is clear.
When to include units in your calculation
Units should appear at minimum on the final answer line of every step. The safest habit, and the one Times Edu tutors teach from the first lesson, is to include units on every substitution line as well.
| Quantity | Correct unit | Common error |
|---|---|---|
| Moles | mol | No unit written |
| Mass | g or kg | Mixing g and kg in same calculation |
| Volume | dm3 or cm3 | Forgetting to convert cm3 to dm3 |
| Concentration | mol/dm3 | Writing mol/L without acknowledging the equivalence |
| Molar volume | dm3/mol | Omitting the constant entirely |
Missing units on a final answer line can cost one mark directly. On a four-mark calculation, that is 25% of the available credit lost to a habit that takes two seconds to fix.
Why you should avoid rounding intermediate answers
Rounding intermediate answers introduces compounding errors. If you round 3.333… To 3.3 after Step 1 and then use 3.3 in Step 2, the error in Step 2 compounds on the error you introduced in Step 1, and your final answer may differ from the expected value by enough to fall outside the accepted range in the mark scheme.
The correct approach is to carry the full calculator display value through every intermediate step and round only the final answer, to the number of significant figures specified in the question or, if unspecified, to three significant figures.
Drawing on years of experience at Times Edu reviewing student papers, compounding rounding errors account for a significant proportion of lost marks in otherwise well-structured calculation answers.
How mark schemes treat correct answers without working
Cambridge mark schemes contain a category sometimes labelled “correct answer only” (cao), which means the mark is available even without working. However, this designation applies to simple one-step calculations, not to multi-step questions.
For any question worth two marks or more, the marks are almost always split between method marks and an answer mark. Without visible working, only the answer mark is accessible, which means the maximum achievable score on a three-mark question answered without working is one mark.
A common mistake we see is students assuming that getting the right number guarantees full marks. It guarantees the answer mark. The method marks require the method to be visible.
Common mistakes when showing Chemistry working
| Mistake | Why it costs marks | The fix |
|---|---|---|
| Horizontal chaining of steps | Examiner cannot identify which step earns which mark | Work vertically, one step per line |
| Omitting labels on numbers | Examiner cannot award intermediate marks for unlabelled values | Label every quantity: “Moles of NaOH =” |
| Skipping the mole ratio line | Loses the ratio method mark even if the answer is correct | Always write the ratio explicitly from the equation |
| Rounding intermediate answers | Compounding error takes final answer outside accepted range | Carry full calculator value until the final step |
| Forgetting unit conversion | dm3/cm3 error produces answer 1000x too large or small | Write the conversion as a visible, labelled step |
| Writing the formula without substituting | Formula mark may be awarded, but substitution mark is not | Always write the substitution line separately |
| Not writing the balanced equation | Cannot demonstrate where the mole ratio came from | Copy or write the balanced equation at the start |
Frequently asked questions
Do you have to show working in IGCSE Chemistry?
You are not always explicitly instructed to, but the mark scheme allocates marks to individual steps. Those marks cannot be awarded without visible working, so the practical answer is yes, always show working on any calculation worth more than one mark.
Can you get full marks without showing working in IGCSE Chemistry?
Only on single-step, one-mark calculations. On any multi-step question, method marks are only accessible through visible working. A correct final answer on a three-mark question without working earns, at most, one mark.
What does show your working mean in an IGCSE Chemistry question?
It means writing the formula you are using, substituting the numbers into it, and recording the result of each step before moving to the next. Each step should be on its own line and labelled with the quantity it represents.
Can you get method marks if your final Chemistry answer is wrong?
Yes. This is the core benefit of showing working. The Error Carried Forward principle means that if you use a wrong intermediate value correctly in subsequent steps, those subsequent steps still earn their method marks.
Should you write the formula before doing a Chemistry calculation?
Yes, always. Writing the formula first earns the formula mark independently of whether your substitution or arithmetic is correct. It takes three seconds and protects one mark per step.
Should units be shown in every step of a Chemistry calculation?
At minimum, units must appear on the final answer. Including units at the substitution step as well is the safer habit and prevents the type of unit-conversion error that loses marks silently.
How should I lay out calculation working in IGCSE Chemistry?
Work vertically down the page. Label each line with the quantity being calculated. Use the N.M.R. Framework for mole calculations, a column table for empirical formula questions, and a two-step layout for percentage yield. Never chain operations horizontally across a single line.
Conclusion
At Times Edu, our specialist IGCSE Chemistry tutors work 1-on-1 with students to build these habits from the first session, reviewing real past paper mark schemes so students understand exactly how each step earns credit. If your child is preparing for Cambridge IGCSE Chemistry 0620 and you want a personalised academic roadmap that identifies where marks are currently being lost and how to recover them, book a consultation with our team. The gap between a Grade 5 and a Grade 7 in IGCSE Chemistry calculations is almost always a presentation problem, not a knowledge problem, and it is entirely fixable with the right guidance.
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