2025/2026/2027/2028 IGCSE  Chemistry Revision   Notes  

• Tip 1: If you have been asked to   Describe how to prepare pure dry crystals of  of a soluble salt, example sodium sulfate from an aqueous solution of sodium sulfate, then  your method must include the following :

Evaporate to point of crystallization . Then  heat to form a saturated solution and then allow it to cool . Then  filter the  crystals and  dry with filter paper . In case you wish to use an oven for drying, then  you must mention, dry in drying oven . 

Note: You lose marks if you do not mention the word' drying'

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• Exam Tips for [Complete Organic Chemistry]
• Homologous series:
• Tip 1: If you have to explain the meaning of the term homologous series, then  in your answer it is mandatory to mention: Homologous series are compounds with similar chemical properties and  same functional group .
• Hydrocarbons:
• Tip 1: If you have to state the meaning of the term hydrocarbon, then it is essential to state it in this way: Hydrocarbons are compounds containing carbon and hydrogen only
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• Note: You lose marks if you do not mention the word'only' 

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• Exam Tips for [Stoichiometry]
• Equations:
• Tip 1: When you have been given a word reaction and asked to predict the products of that reaction and state your answer as a symbol equation:
• For Example:
•         Sodium    reacts    with    fluorine    to    form    sodium    fluoride.  Write a symbol equation for this reaction.[2],
• Note:
• You get one mark for writing the symbol of the product correctly. You get  complete marks for writing the complete symbol equation correctly.
• Suggestion:
• Even if you are not sure of all the symbols of reactants and products, write all that you know. That way, you  might be fortunate enough to score at least a mark. Remember, every mark counts!
• Note: You lose marks if you write the above statement , but  forget to mention the word' chemical'
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• Exam Tips for [Atoms, Elements and Compounds]
• Comparing properties of compounds
• Tip 1: While comparing  the melting points  of  two compounds, in terms of structure and bonding, use words such as weaker/ stronger and don't just say ' weak or strong'. This is mandatory as per Cambridge examiner guidelines.
• Example: Explain, in terms of structure and bonding, why SnCl₄ has a much lower melting point than SnO.
• Mark Scheme:
• M1 attraction between molecules or inter molecular forces in tin(IV) chloride M2 tin(II) oxide has a giant ionic structure M3 weaker attraction (between particles) in tin(IV) chloride ORA
• Ideal Answer:
• Tin(IV) chloride (SnCl) has a much lower melting point than tin(II) oxide (SnO) because SnCl consists of simple molecules held together by inter molecular forces. In contrast, SnO has a giant ionic structure with strong electrostatic forces between oppositely charged ions. The inter molecular forces in SnCl are significantly weaker than the strong ionic bonds in SnO, requiring much less energy to overcome, resulting in a lower melting point.
• Note:

(1)While comparing  the properties  of  two  or more compounds, in terms of structure and bonding, use words such as weaker/ stronger and don't just say ' weak or strong'. This is mandatory as per Cambridge examiner guidelines.

(2) Ther alphabets er are underlined in the above mark scheme, indicating that it is mandatory to use comparison.

Tip 2: Dot -Cross Diagrams are Examiners  favourite. It is important to practice drawing them.

• Exam Tips for [Acids, Bases and Salts]
• Making Salts:
• Tip 1:In salt-making, Powdered  metal is added to dilute acid. The mixture is stirred. More zinc is added, with stirring, until the zinc is in excess. Zn(s) + H₂SO₄(aq) ? ZnSO₄(aq) + H₂(g) The mixture is then filtered.

Example:

Powdered   zinc is added to dilute  sulfuric acid. The mixture is stirred. More zinc is added, with stirring, until the zinc is in excess. Zn(s) + H2SO₄(aq) -> ZnSO₄(aq) + H₂(g) The mixture is then filtered. Since a gas is evolved, the following could be the observations that indicate that the metal zinc is in excess:

(1.) solid remains[ or the solid  is undissolved

(2.)bubbling[ or effervescence or fizzing stops ]

Note: Since hydrogen is colourless, we cannot mention any colour as a part of the observation for the gas

• Exam Tips for [Chemical Reactions]
• Common Mistakes:
• Tip 1:You lose marks if you state the following as the characteristics of an equilibrium :
• (1) forward reaction = reverse reaction (without rate)
• (2) rates of reaction are constant (as opposed to equal)
• (3)concentrations of reactants and products are the same (as opposed to constant).

Correct is:

• Tip 1:The characteristics of an equilibrium are :
• (1)The rate of the  forward reaction = rate of the reverse reaction 
• (2) rates of reaction are equal 
• (3)concentrations of reactants and products are the constant