Chemistry (9701) 考试技巧

计算器程序

常见错误

1. 1high涉及分数: 2Chemical energetics (Physical chemistry (AS Level))

   Failing to state 'per mole of water formed' when defining the standard enthalpy change of neutralisation.

   如何避免: Always specify that the energy change is associated with the formation of exactly one mole of water from the neutralisation reaction of an acid and alkali under standard conditions.
2. 2high涉及分数: 1Chemical energetics (Physical chemistry (AS Level))

   Using the mass of solid solute instead of the total solution mass (i.e. volume converted to grams) in the thermal heat capacity calculation q = mcΔT.

   如何避免: Identify the aqueous solution volume as the source of the mass (m) in the equation. For example, if adding solid to 25.0 cm³ of water/acid, use 25.0g as 'm', not the solid's mass.
3. 3medium涉及分数: 1Ionisation energy (Atomic structure)

   Omitting the gas state symbol '(g)' when defining or constructing balanced equations representing successive ionisation processes.

   如何避免: Always write the gaseous state symbol for both the reactant and product species in ionisation energy equations (e.g. X(g) -> X+(g) + e-).
4. 4high涉及分数: 1Reacting masses and volumes (of solutions and gases) (Atoms, molecules and stoichiometry)

   Recording burette readings to only 1 decimal place instead of the required 2 decimal places (ending in .00 or .05) in titration files.

   如何避免: Ensure every single initial and final burette reading in your results table ends in .00 or .05 (e.g., 22.10 cm³ or 22.15 cm³).
5. 5medium涉及分数: 1Reacting masses and volumes (of solutions and gases) (Atoms, molecules and stoichiometry)

   Failing to double the single reading uncertainty when calculating the percentage error for thermometers or mass balance measurements.

   如何避免: Because mass-by-difference and temperature-change calculations involve two separate readings, multiply the maximum error of the apparatus by 2 before dividing by the experimental value.
6. 6high涉及分数: 2Characteristic organic reactions (An introduction to AS Level organic chemistry)

   Starting curly arrows in organic mechanisms from carbon nuclei or empty spaces instead of bonds or lone pairs.

   如何避免: Position the start of your curly arrow precisely on a lone pair of electrons (e.g., on a nucleophile) or on the center of a bond (like a double bond or carbon-halogen bond) and end it precisely on the target atom.
7. 7high涉及分数: 1Chemical energetics (Physical chemistry (AS Level))

   Omitting explicit positive (+) or negative (-) signs from final calculated values of enthalpy changes.

   如何避免: Always state the explicit mathematical sign for any thermodynamic value. For example, write -57.3 kJ/mol for an exothermic process, not just 57.3.