The “hard” parts of IGCSE Chemistry (0620) usually aren’t the topics with the most content. They’re the ones where marks are lost through setup errors, weak explanations, or messy practical thinking. These are the areas most students struggle with, plus the simplest ways to get them under control.

1) Stoichiometry (moles, equations, concentration, yields)

Why it feels hard: one small mistake early (units, equation balance, mole ratio) wrecks the whole answer.

How to master it

• Use one fixed layout every single time: balance → write mole ratio → convert to moles → apply ratio → convert back → units.
• Drill these five until they’re automatic: Mr, moles, concentration (mol/dm³), titration, limiting reactant.
• Train “unit discipline”: dm³ vs cm³, g vs kg, and always show working.

Quick practice: do 10 short mole questions daily for a week instead of one long worksheet once.

2) Electrolysis and redox (especially aqueous electrolysis)

Why it feels hard: students memorise products without understanding why ions win at electrodes.

How to master it

• Learn the decision rule: identify ions present → check if aqueous → use reactivity series/selective discharge ideas → write products at each electrode.
• Practise writing half-equations even when they aren’t demanded. It forces accuracy.
• Make a one-page grid: molten vs aqueous, inert vs reactive electrodes, common electrolytes.

Quick practice: explain each answer in one line: “X forms because it is less reactive than hydrogen / halides discharge except fluoride / etc.”

3) Bonding and structure (linking structure to properties)

Why it feels hard: answers need cause-and-effect, not a list of facts.

How to master it

• Learn property chains:
  • ionic: strong electrostatic attraction → high mp/bp; mobile ions when molten/aqueous → conducts
  • simple molecular: weak intermolecular forces → low mp/bp; no mobile charges → doesn’t conduct
  • giant covalent: many strong covalent bonds → very high mp; graphite conducts due to delocalised electrons
  • metallic: delocalised electrons → conducts; layers can slide → malleable
• Practise “because” sentences. If you can’t include the reason, you’ll drop marks.

Quick practice: pick one substance (NaCl, iodine, diamond, graphite, aluminium) and write 3 properties with reasons.

4) Organic chemistry (naming, reactions, polymers)

Why it feels hard: it’s easy to mix up functional groups, conditions, and reaction types.

How to master it

• Build a mini toolkit:
  • functional group recognition (alkane, alkene, alcohol, acid, ester)
  • key tests (bromine water for alkenes)
  • core reactions (addition, combustion, fermentation, cracking, polymerisation)
• Practise naming daily. Speed matters because organic questions can be “easy marks” if you’re fluent.

Quick practice: write five structures and name them, then swap: given names, draw structures.

5) Rates, energetics, and graphs (application marks)

Why it feels hard: questions look unfamiliar even when the concept is simple.

How to master it

• Memorise the language for graphs: steeper gradient = faster rate, plateau = reaction finished, higher temperature = more frequent successful collisions.
• For energetics: link diagrams to ideas: activation energy, exo vs endo, and what catalysts do (lower Ea).
• Use short, exam-style explanations: one clear cause, one effect.

Quick practice: redo past-paper graph questions and rewrite your explanations using mark-scheme keywords.

6) Acids, bases, salts (salt preparation and ionic equations)

Why it feels hard: students pick the wrong method or forget what “soluble” changes.

How to master it

• Learn salt prep as a decision:
  • soluble salt from acid + alkali → titration
  • soluble salt from acid + insoluble base/carbonate → excess solid, filter, crystallise
  • insoluble salt → precipitation, filter, wash, dry
• Practise ionic equations: remove spectators, keep charges balanced.

Quick practice: take 6 salts and write the correct preparation method + one balanced equation each.

7) Practical skills and Alternative to Practical (tables, errors, improvements)

Why it feels hard: it’s not “revision” in the usual sense, so it gets ignored.

How to master it

• Train these habits:
  • tables with headings + units
  • repeat readings and average
  • specific errors (heat loss, parallax, incomplete reaction, endpoint judgement)
  • realistic improvements (insulation, lid, pipette/burette, data logger, repeat trials)
• Learn qualitative tests (gases, ions, flame tests) from one sheet and recall them fast.

Quick practice: do one Paper 6 style question every two days and mark it strictly.

The fastest way to raise your grade in 3 weeks

• Week 1: stoichiometry + bonding (daily drills)
• Week 2: electrolysis + acids/salts + qualitative tests
• Week 3: full papers + mistake-log fixes (one timed paper every other day)

A simple “mastery rule”

If you can (1) explain the idea in one clean sentence, (2) solve a standard question without pausing, and (3) handle a past-paper twist without panicking, that topic is exam-ready. If not, it goes back into your drill list until it is.