Edexcel IGCSE Science (Double Award) Past Papers

Common mistake: A very common mistake is ignoring the molar ratios (e.g., 2:1 or 3:2) provided in balanced chemical equations.

How to solve it: Always check the coefficients in the chemical equation and incorporate them into your mole-to-mass or mole-to-mole conversions.

Common mistake: Students often confuse the strong covalent bonds within a molecule with the weak intermolecular forces between molecules. Phrases like "weak forces between the bonds" are frequently seen and score no marks.

How to solve it: Use "covalent bonds" only when discussing the atoms inside a molecule and "intermolecular forces" when discussing boiling/melting points of simple molecular substances.

Common mistake: When explaining high or low melting points, students often say "more" or "less" energy is needed.

How to solve it: Use absolute terms. Giant structures require a "large amount of energy" to break strong bonds, while simple molecules require "little energy" to overcome weak forces

Common mistake: There is significant confusion between radioactive contamination (the unwanted presence of radioactive atoms on or in an object) and irradiation (exposure to radiation without becoming radioactive).

How to solve it: Remember that if a source remains in a fixed location (like thorium in a solid work surface), it can only irradiate nearby objects; contamination only occurs if physical particles of the radioactive material are moved onto another surface.

Common mistake: For space physics, students often fail to draw the Sun or Earth at the centre of the orbit for planets or moons. In magnetism, field lines are sometimes drawn crossing each other or with incorrect arrow directions.

How to solve it: Use a sharp pencil and compass where possible. Stick to 2D drawings (avoid 3D perspective as it obscures the shape) and always label the direction of field lines as North to South.