Most Common Mistakes Students Make In O Level and IGCSE Chemistry Paper 2 / Paper 4 & How To Avoid Them
Most Common Mistakes Students Make In Chemistry Paper 2 & How To Avoid Them
1. Misreading the Question
Where Students Make Mistakes
- Skipping key words that change the meaning of the question.
- Not noticing specific conditions:
- Temperature
- Pressure
- Catalyst
- Aqueous vs molten
- Concentration
- Assuming the answer instead of analysing what is actually asked.
- Forgetting to read diagrams, labels, and units attached to data.
How A Students Avoid This
- Underline:
- All numbers
- All units
- All formulas
- All specific conditions
- Read every question twice:
- First for understanding
- Second for detail
- Identify the command word before writing anything.
- Mentally summarise the question in 5 seconds:
- “What exactly are they asking me?”
2. Writing Long Paragraphs Instead of Bullet Points
Where Students Go Wrong
- Writing answers in big paragraphs that hide keywords.
- Mixing explanations and definitions in one chunk.
- Adding unnecessary information.
- Using unclear sentences that examiners cannot award marks for.
How A Students Avoid This
- One idea per bullet.
- Short, crisp bullets:
- Cause
- Mechanism
- Effect
- Place keywords in visible bullets so examiners can award marks instantly.
- Use line spacing to separate independent ideas.
3. Incorrect Use of Command Words
Where Students Go Wrong
- Writing “explanations” for “state” questions.
- Giving descriptions instead of mechanism-based explanations.
- Predicting without using patterns.
- Mixing up compare vs contrast vs describe.
How To Fix This
- State:
- One direct fact.
- Describe:
- List characteristics.
- Explain:
- Reason + mechanism + conclusion.
- Predict:
- Use known trends.
- Compare:
- Similarities + differences.
- Suggest:
- Give logical, scientifically valid possibilities.
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Free Material
4. Calculation Mistakes Due to Wrong Units
Common Student Errors
- Forgetting to convert cm³ to dm³.
- Using 24 instead of 24,000 or vice versa.
- Forgetting units entirely.
- Mixing up g/dm³ and mol/dm³.
- Using wrong significant figures.
A-Student Method
- Convert all volumes to dm³ immediately.
- Write formulas before inserting values.
- Include units in every substitution.
- Round answers only at the final step.
- Use the same number of significant figures as the question.
5. Not Showing Working Clearly
Where Students Go Wrong
- Writing final answer without steps.
- Not showing how moles were calculated.
- Mixing numbers and explanations together.
How To Avoid This
- Write formula → substitute → solve.
- Separate each step with a line.
- Label every step.
- Clearly circle the final answer.
6. Memorising Definitions Incorrectly
Where Students Make Mistakes
- Missing key words:
- “Simplest” in empirical formula
- “Proton donors” in acids
- “Gain of electrons” in reduction
- Mixing up similar definitions.
- Writing vague lines like “it is when something reacts”.
How To Avoid
- Use precise one-line bullets.
- Memorise 5 definitions daily.
- Keep all definitions in a dedicated sheet.
7. Incorrect or Unaccepted Colour Descriptions
Where Students Go Wrong
- Using non-scientific descriptions:
- “Bluish green”
- “Pale white”
- “Cloudy water”
- “Darkish brown”
- Writing “clear” instead of “colourless”.
Correct Method
- Accepted colours:
- Blue precipitate
- Green precipitate
- Brown precipitate
- White precipitate
- Colourless solution
- Never write “clear”.
8. Not Following the Explanation Formula
Where Students Go Wrong
- Skipping steps between cause and effect.
- Repeating the question instead of answering it.
- Writing random effects without mechanism.
- Using emotional language.
Correct A-Student Explanation Formula
- Cause:
- What changed?
- Mechanism:
- How did it affect particles/bonds/structure?
- Effect:
- What happened finally?
Example
- Why gases diffuse faster at higher temperature:
- Particles have more kinetic energy
- They move faster
- They collide and spread out more quickly
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Free Material
9. Wrong State Symbols
Where Students Go Wrong
- Forgetting state symbols completely.
- Writing (l) instead of (aq).
- Writing (g) for dissolved gases.
- Writing (s) for dissolved solids.
Correct Rules
- (aq): Ions dissolved in water
- (s): Precipitate or solid
- (l): Pure liquid
- (g): Gas
10. Incorrect Chemical Equations
Where Students Go Wrong
- Wrong formula (e.g., NAOH instead of NaOH).
- Wrong balancing.
- Forgetting ionic charges.
- Removing the wrong spectator ions.
How To Fix This
- Write full balanced equation first.
- Identify spectator ions clearly.
- Remove only those ions.
- Keep charges accurate and visible.
- Always check:
- Atom balance
- Charge balance
11. Poor Understanding of Ion Tests
Where Students Make Mistakes
- Confusing:
- Sodium hydroxide test vs ammonia test
- Flame test colours
- White precipitate variations
- Mixing transition metal colour patterns.
Correct Learning Method
- Separate sheets for:
- Cations
- Anions
- Flame tests
- Gas tests
- Use pattern learning:
- Cu²⁺ → blue
- Fe²⁺ → green
- Fe³⁺ → brown
12. Weak Graph and Table Answers
Where Students Go Wrong
- Graphs too small.
- No labels.
- No units.
- Incorrect scale choice.
- Using dot-to-dot instead of best-fit line.
Correct Graph Method
- Use at least 50–70% of graph space.
- Label both axes with units.
- Use small crosses.
- Draw best-fit line smoothly.
- Use a large triangle for gradient.
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Free Material
13. Weak Practical Improvements
Where Students Go Wrong
- Writing vague improvements.
- Suggesting impossible steps.
- Repeating the same improvement everytime.
- Missing key experimental limitations.
A-Level Improvement Style Needed
- Specific:
- “Use a digital thermometer instead of a mercury thermometer.”
- Scientific:
- “Use insulation to reduce heat loss.”
- Actionable:
- “Repeat experiment to get average results.”
14. Forgetting Key Structural Ideas in Explanations
Where Students Go Wrong
- Writing:
- “Metals have electrons”
- “Graphite is strong”
- “Ionic compounds have bonds”
- Leaving out structures that make the explanation correct.
Correct Structural Links
- Ionic compounds:
- Giant lattice
- Strong electrostatic forces
- Metals:
- Positive ions + delocalised electrons
- Simple molecules:
- Weak intermolecular forces
- Giant covalent:
- Strong covalent bonds throughout
15. Weak Organic Chemistry Naming
Where Students Go Wrong
- Counting carbon atoms incorrectly.
- Forgetting functional group priority.
- Using wrong suffix.
- Confusing alkene with alkane.
Correct Technique
- Identify longest carbon chain.
- Identify functional group.
- Number from nearest functional group.
- Use correct suffix:
- -ane
- -ene
- -ol
- -oic acid
- Draw before naming.
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Chemistry Free Material
16. Not Learning Solubility Rules Properly
Where Students Go Wrong
- Guessing solubility.
- Memorising rules incorrectly.
Correct Solubility Rules
- All nitrates soluble
- All sodium/potassium/ammonium salts soluble
- Most chlorides soluble except:
- Silver chloride
- Lead chloride
- Most sulfates soluble except:
- Barium sulfate
- Lead sulfate
- Calcium sulfate
- Most carbonates insoluble except:
- Sodium carbonate
- Potassium carbonate
- Ammonium carbonate
17. Overwriting or Underwriting Answers
Where Students Go Wrong
- Writing too much where only one line is needed.
- Writing too little where explanation is required.
Correct Response Length
- State:
- One bullet
- Describe:
- 2–3 bullets
- Explain:
- 3–4 bullets
- Compare:
- 3 similarities + 3 differences
18. Confusing Reactivity Series Logic
Where Students Go Wrong
- Reversing displacement logic.
- Forgetting that more reactive metals react more with water/steam.
- Assuming reactivity based on boiling point or melting point.
Correct Logic
- More reactive metal → displaces less reactive metal.
- Potassium, sodium, calcium → react violently with water.
- Magnesium → reacts with steam, not cold water.
- Copper, silver, gold → do not react with acids.
