IGCSE Chemistry (0620): Exam Technique for the October/November 2026 Series

Chemistry 0620 sits alongside Mathematics and Biology among the most-entered Cambridge subjects for Kenyan candidates, and its mark schemes are unusually consistent about where credit lives. Three habits, all fixable in the remaining weeks, separate the grades.

This guide takes each habit in turn, adds worked practice calculations you can copy into a revision book, and finishes with a two-week routine for the end of the series. The practice items are written for this guide; they are not Cambridge questions and are not taken from past papers.

Balance with coefficients, never by editing a formula

Asked to balance H₂ + O₂ → H₂O, a losing script changes the water to H₂O₂. That is no longer water, and the question scores zero. Only the large numbers in front of a formula may change: 2H₂ + O₂ → 2H₂O. Candidates who understand that a subscript defines the substance stop making this error permanently.

A balancing routine that always works

1. Write every formula correctly first, and then treat the formulas as fixed.
2. Count atoms of each element on both sides, writing the counts underneath.
3. Balance the element that appears in the fewest substances first; leave hydrogen and oxygen until last if they appear in several places.
4. Recount everything at the end. If a coefficient can be divided through by a common factor, simplify.
5. Add state symbols, (s), (l), (g) and (aq), whenever the question asks for them.

Practice: balance CH₄ + O₂ → CO₂ + H₂O. Carbon is already balanced. Four hydrogens on the left need 2H₂O on the right. That gives four oxygens on the right (two in CO₂, two in 2H₂O), so 2O₂ on the left: CH₄ + 2O₂ → CO₂ + 2H₂O.

Mole calculations: the working is the mark

The most common systematic loss is the volume conversion: concentration is per litre (per dm³), and a candidate who divides by 500 instead of 0.5 has thrown away the question. Write the conversion as its own line, every time.

Worked practice calculations

Practice 1, concentration. 0.2 mol of a solute is dissolved to make 250 cm³ of solution. Find the concentration.

• Volume = 250 ÷ 1000 = 0.25 dm³
• Concentration = moles ÷ volume = 0.2 ÷ 0.25 = 0.8 mol/dm³

Practice 2, gas volume. What volume does 0.5 mol of a gas occupy at room temperature and pressure? Use a molar gas volume of 24 dm³ at r.t.p.

• Volume = moles × 24 = 0.5 × 24 = 12 dm³

Practice 3, empirical formula. A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass.

• Divide by A_r: C 40.0 ÷ 12 = 3.33; H 6.7 ÷ 1 = 6.7; O 53.3 ÷ 16 = 3.33
• Divide by the smallest: C 1, H 2, O 1
• Empirical formula: CH₂O

In each case, notice that every step is a separate written line. That is not neatness for its own sake. If the final number is wrong, those lines are where the method marks are found.

Observation is what you see, conclusion is what you deduce

Practical and alternative-to-practical papers separate these ruthlessly. "Effervescence, and a colourless gas that turns limewater milky" is an observation. "Carbon dioxide is produced" is a conclusion. Write the conclusion in the observation column and the mark is gone, because the gas was never seen, it was inferred. The same discipline pays in the gas tests, which recur every series: hydrogen pops with a lighted splint, oxygen relights a glowing one, carbon dioxide turns limewater milky, ammonia turns damp red litmus blue, chlorine bleaches damp litmus.

Other practical habits that protect marks

• Units in table headings, not in the cells. Write "Volume / cm³" once at the top, then plain numbers below.
• Consistent decimal places. Burette readings are usually recorded to the same precision throughout; mixing 24 and 24.15 in one table looks careless and can cost a mark.
• Graphs with sensible scales. Use most of the grid, label both axes with quantity and unit, and draw a smooth best-fit line or curve rather than joining dots.
• Named improvements. When asked how to improve an experiment, give a specific change and say why it helps. "Be more careful" earns nothing.

Turning past papers into marks

Doing a paper is not the same as learning from it. The value is in what happens after the last question. A simple marking routine:

1. Sit the paper to time, with no notes.
2. Mark it the same day, strictly against the mark scheme, line by line.
3. For each dropped mark, write "content" (did not know it) or "technique" (knew it, lost it in how it was written).
4. Fix content with short targeted notes. Fix technique by rewriting the answer correctly straight away.
5. Keep a running technique list and read it before the next paper.

Most candidates discover that more than they expected falls into the technique column. That is good news, because technique improves in days, not weeks.

This continues our November series set: Biology 0610, Mathematics 0580 and English 0500 are already live. Structured revision for the seven most-entered subjects is packaged in the IGCSE Countdown Bundle for November 2026, and live teaching runs through the IGCSE training programme.

Key Takeaways

• Balance equations with coefficients only; changing a subscript changes the substance.
• Mole questions are marked on the written method; convert volumes to litres on their own line.
• Observations are seen; conclusions are deduced. The columns are not interchangeable.
• The five gas tests recur every series and are close to guaranteed marks.
• Practise five papers strictly against the mark scheme rather than fifteen loosely.

Frequently Asked Questions

Core or Extended?

Grades above C require Extended. A candidate holding 60 per cent on Extended past papers belongs there.

Is the periodic table provided?

Yes, in every paper. Learning to read group and period information from it quickly is part of preparation.

How different is 0620 from CBC Integrated Science?

They are separate curricula, examined in different styles, and this site keeps their materials strictly apart. Revise each on its own terms.

What should the last two weeks look like?

Past papers under time, marked against the scheme the same day, with every dropped mark classified as content or technique and the technique list drilled directly.