A seemingly easy paper that secretly challenged the Pure/Combined Students’ foundation without them realising.

2020 has been a really different year. A year that has challenged many of us to adapt and move away from our normal routines. For students taking the ‘O’ levels this year, it was even more so. 

From home-based learning, to a shortened syllabus, to taking exams with their face masks, the students have had quite a different experience taking the ‘O’ levels this year.

This year’s national examination was unique and unlike other precedent ‘O’ level examinations: 

  • Chapters were removed from the syllabus (For Chemistry, five chapters of Organic Chemistry)
  • Questioned related to those chapters were struck off. 
  • The weightage of each mark became greater (meaning less room for mistakes).
  • Bonus: Students had less to memorise and more time to complete each question. 

With less topics to memorise and more time to complete the paper, it might seem that students this year would have an easier time compared to previous years. Overall, both the Combined Chemistry and Pure Chemistry Paper 2 questions are manageable and easy to score. Mole calculation questions were extremely easy, but there were some tricky questions that could have caught many students off-guard if they were not fully prepared or have a shaky chemistry foundation.

In this review, we take a look at some of the questions that might have tricked many students and caused them their marks.

1. Definition

We know, it is a pain to memorise all the definitions in the textbook. But if you made the effort to remember them, you would have secured the few marks!

Definitions tested for

  • Combined Chemistry: Exothermic, Relative Molecular Mass, Kinetic Particle Theory
  • Pure Chemistry:          Collision Theory, Uses of Fractions in Crude Oil, Macromolecule, Addition Polymerisation (Removed)

2. Questions on Foundation and Understanding

If you went into the examination thinking that you have memorised all the content and the types of questions that always come out, you might have stumbled on some of the questions that challenged your true understanding of each topic.

At Habitat Learning Centre, we have always emphasised on the understanding of each topic and encouraged students to ask if they are in doubt, instead of solely relying on formulas and trends that will be useless when faced with such questions. It is always important to fully understand the question before jumping in to solve the question seemingly thinking that it might have attempted it before.

For Combined Chemistry

  • Stating the chemical formula or Tantalum chloride and Tantalum oxide. Knowing that Tantalum is a metal, ionic compounds should be formed even though it contains five valence electrons.
  • Using Kinetic Particle Theory to explain increasing melting point down Group VII. Students will need to relate the change in physical states of the halogens down the group to explain the increasing melting point.

For Pure Chemistry

  • Understanding what metal hydrides are and their chemical formula (MH instead of HM).
  • Understanding the relationship between mole, mass and molecular mass. One of the more challenging questions involved the statements made by Jean, Beth and Ryan about the mole of substance formed from each gram of reactant used and deducing the mass change of each hydride down the group. Students who do not understand mole and the relationship between the variables would find themselves making mistakes in this question. 

3. Comprehensive Skills

Time must be taken to read the questions carefully and comprehend the passage and questions asked.

Similar to previous years, you will find such questions in Section B of the paper. Students who did not invest enough time to understand the passage in the question might find themselves clueless on how to solve these questions. The explanation and evidence can always be found in the passage!

For Pure Chemistry

  • Understanding De-icers
    • Not a text-book example, students might struggle with this question if they haven’t practiced much application related questions.
    • The questions in this part are not challenging, and many of the answers can be found in the passage.
  • Comparing different models to represent a molecule
    • To an advanced student, this question should not be challenging as the models show many discrepancies such as the relative size of the atoms and the different bond lengths, allowing them to conclude.
    • Additional information such as the bond length and atomic radius would help those students who had no clue but invested the time in reading the question.

Most students should find the other questions manageable. Head on to our Facebook page to find our suggested solutions!

For enquiries on Secondary Chemistry or Junior College Chemistry tuition, visit us at habitatlearningcentre.com or contact Ms Song at +65 97953323.

Written by:
Leon Choo Lead Tutor,
Chemistry and Physics Specialist
Habitat Learning Centre Pte Ltd