Chemistry is one of the more popular electives that Hong Kong students opt for, and last year 14,679 candidates took the DSE chemistry exam. With that in mind, and with this year’s DSE exam fast approaching, Winnie Chan – a chemistry tutor from tutoring centre Modern Education, and top DSE scorers Melody Tam Lok-man and Moses Lam Ka-nam share their tips and tricks with Young Post readers for how to study this subject more effectively, and what to during the exam.
Chan says that one of the most important things a student should do is to clearly state the units and to not mix them up. For example, if they are expressing the concentration of a solution, then use M as a unit. M refers to molarity. If a question asks a student to calculate the gas concentration of a solution, however, don’t use M – use mol dm-3 instead. Chan says they need to calculate units too, like the equilibrium constant and the rate constant.
“You can put the units into the calculation. So, if Keq = [A][B], the unit will calculated from M x M = M2.”
Moses, 18, says that students should try to memorise as much basic chemistry knowledge as possible, like the physical properties and the hazard warning labels of common chemicals.
“Studying definitions, like Hess’s law and the standard enthalpy of reaction is good too,” he says.
Moses recommends practising A-level or HKCEE papers for certain topics, such as equilibrium and organic chemistry. The former topic, he adds, might require a person to figure out the equilibrium shift, and the latter might ask someone to deduce an organic compound. Practising past papers is a good way get familiar with different question types.
Moses says it would be wise for students to also spend time on the more unpopular topics too, as he has noticed a trend towards asking students more about these topics. For instance, Q15 in last year’s DSE Chemistry Paper 1A asked students about the half equations for the discharge of secondary cells.
A lot of students lose marks when it comes to calculations. Melody, 19, says that there are certain steps to calculation that can be followed. For example, there are three steps when it comes to calculating empirical formula: (1) mass (g); (2) number of moles; (3) relative number of moles.
“Organise your answer in a logical way so your examiners can follow your ideas easily,” Chan says. Being able to clearly communicate answers earns a student marks. If a short essay in Paper 1B is worth five marks, Chan says four marks are given for having four correct points. The remaining mark is given if the answers show in-depth chemistry knowledge and is in complete sentences.
If a question asks a student to state the expected observation about the change in a chemical’s colour, Chan says should to show the colour change like this: “the solution changes from blue to green”. Many students forget to state what the original colour was.
Unless the equation is about enthalpy change, Chan says not to write state symbols, such as (s), (l), (g), and (aq), as marks will be deducted for adding the wrong state symbols to the answers. Moses says that questions should be read carefully to pick up keywords. For example, Q12 in 2013 DSE Paper 1B gave the volume of a sealed container, which is 10.0 dm3. He says that if students overlooked the stated volume, the final answer that they gave would be completely wrong.
Chan also suggests that students identify and use the right keywords in order to gain marks. For instance, Q2(c) in Chemistry Practice Paper 1B asks students to suggest a limitation to preserving wine by removing air from an opened bottle of wine and then sealing it. The keywords for the answer were “volatile organic compounds”, and if the answer didn’t include this phrase, students were not awarded marks.
Most importantly, students need to manage their time well, especially for Paper One. They have two and a half hours for Paper One, and Chan suggests that they should spend at most 50 minutes on Section A, the multiple choice questions. The remaining 100 minutes should be spent on Section B, which is worth around 80 marks.
Edited by Ginny Wong