AQA GCSE Chemistry Past Papers

Common mistake: The most frequent error is the imprecise use of the terms atoms, ions, and molecules, which are often used interchangeably or omitted entirely. For example, students often refer to "calcium" and "chlorine" reacting rather than specifying calcium atoms and chlorine atoms.

How to solve it: Always identify the specific particle involved in a process; use "ions" when discussing electrolysis or ionic bonding and "molecules" for covalent substances.

Common mistake: Students often incorrectly state that intermolecular forces exist in giant structures like diamond, graphite, or metals. These substances are held together by strong covalent, ionic, or metallic bonds, not intermolecular forces.

How to solve it: Reserve the term "intermolecular forces" strictly for small molecules (like methane or water) and use "strong bonds" for giant structures.

Common mistake: A recurring high-demand mistake is failing to convert volumes from cm³ to dm³ before calculating moles in titration questions. Additionally, many students divide by the sum of mass numbers rather than 100 when calculating relative atomic mass from percentages.

How to solve it: Always check units; if a volume is in cm³, divide by 1000 to convert to dm³ before using it in n=c×v

Common mistake: The definition of a weak acid is often given as "partially ionised," but students frequently omit the essential detail that this occurs in aqueous solution. Some also incorrectly state the acid is "ionising" (acting on something else) rather than being "ionised" itself.

How to solve it: Memorise the full definition: a weak acid is partially ionised or dissociated in aqueous solution.

Common mistake: Students often lose credit by referring to protons and neutrons when describing early models like the Plum Pudding or the Bohr model. At the time these models were developed, these subatomic particles had not yet been discovered.

How to solve it: Use only the features present in the specific model requested; for example, the Plum Pudding model only contains electrons embedded in a ball of positive charge.

Common mistake: Many students believe that electric current in a solution is conducted by delocalised electrons rather than mobile ions. Conversely, when describing metals, they often fail to state that electrons move through the structure in a specific direction rather than just "throughout" it.

How to solve it: Remember that ions carry charge in liquids/solutions, while delocalised electrons carry charge in solids like metals and graphite