Assessment Report

New Zealand Scholarship
Chemistry 2020

Standard 93102

 

Part A: Commentary

Candidates who were successful in this examination were those who could show broad understanding of the various aspects of the chemistry curriculum. This included understanding of the pH of aqueous solutions, thermodynamic principles, ionisation of atoms, electrolytic cell processes, organic synthesis, spectroscopy, solubility equilibria, particle interactions in aqueous solutions, quantitative calculations, and thermochemical calculations. These candidates were able to use problem solving skills to apply their knowledge of chemistry to unfamiliar situations.

There were, however, a number of candidates who were unable to progress through many of the questions. These candidates had not adequately prepared for the examination and were unable to show either adequate understanding of chemistry examined or application of their knowledge to the unfamiliar contexts given. It is expected that, regardless of which internal or external standards the candidates may have faced in their schooling, they should be prepared for questions from all areas of the curriculum.

Unsuccessful candidates were often unable to address the intent of a question, giving answers that either lacked understanding of important concepts, or included incorrect scientific ideas. Hydrolysis reactions, particle interactions involving water, and aqueous calculations were all areas of weakness amongst unsuccessful candidates. For example, a number of candidates missed in question 2(a) that water was present in the aqueous solution undergoing electrolysis, and therefore did not identify that water was the strongest reductant. Conversely, other candidates attempted to discuss multiple oxidation-reduction changes occurring simultaneously, despite the question stating that the strongest oxidant reacts at one electrode, and strongest reductant at the other.

Calculations which were approached logically and clearly laid out often enabled candidates to achieve greater outcomes than those with no clear pathway shown. It is essential that candidates are able to solve calculations that involve a different variety of steps than the common methods utilised in NCEA examination questions. For example, question 1(a) required no further understanding than Level 3 pH calculations, but very few candidates were able to construct a logical path towards solving the question when faced with the unfamiliar context of starting with pH values. It is also expected that candidates are able to carry out extended calculations without introducing rounding errors and are able to use correct significant figures and units in line with the data provided in the questions.

Candidates who understood the nature of particles, solutions, and interactions between them, performed significantly better overall in the examination than those who did not have a clear grasp on these core chemistry concepts.

Overall, those candidates who were worthy of scholarship and outstanding scholarship outcomes really stood out in this examination, producing work which was noticeably more detailed and insightful than those who were unsuccessful.


Part B: Report on Performance

Candidates who were awarded Scholarship with Outstanding Performance commonly:

  • calculated the pH and relative concentration of species in the aqueous solution
  • related enthalpy and entropy changes to particles and attractive forces
  • discussed entropy changes in relation to changes in the system and surroundings
  • related bond breaking and bond formation to enthalpy changes
  • communicated clearly the links between subatomic particles, electron configurations, and relative ionisation enthalpies
  • recognised the presence of H2O in aqueous solutions
  • correctly used standard electrode potentials to identify the strongest oxidant and reductant species in ionic solutions
  • completed cell potential calculations, balanced equations, and observations for the given electrolytic processes
  • recognised the role of electrodes in electrolytic cells
  • correctly predicted impacts of changes made to electrolytic cells
  • demonstrated comprehensive understanding of organic reactions
  • drew clear structures for organic compounds and formulae for inorganic reagents
  • completed the organic reaction scheme
  • completed common ion effect calculations using the given solutions to determine the lack of precipitation
  • justified the role of nitric acid with the use of balanced equations and/or calculations
  • correctly predicted the 13C NMR peaks, and clearly linked these to the different carbon environments found in the hydrolysis products
  • compared and contrasted the peaks and position of peaks in the different 13C NMR spectra to justify the unique attributes that could be used to identify the hydrolysis products
  • comprehensively explained particle interactions between water molecules and polar, non-polar, and ionic species
  • used particle interactions to correctly justify the given observations
  • completed calculations for a back titration
  • rounded final answers only
  • correctly calculated the theoretical energy release for the given reaction
  • discussed multiple plausible reasons for the variation in observed energy release
  • gave concise answers to discussion questions
  • gave answers that demonstrated a logical approach to discussing unfamiliar substances
  • completed calculations with logical, well laid out, detailed working, with use of correct significant figures and units

 Candidates who were awarded Scholarship commonly:

  • calculated the concentration of a weak acid (NH3) given the pH of the solution
  • showed an understanding of enthalpy and entropy changes in unfamiliar contexts
  • discussed the dissolving of oxygen gas into water correctly
  • recognised factors which affected ionisation enthalpy values
  • correctly predicted the order of species in relation to their relative ionisation enthalpy values
  • used standard electrode potentials to identify a strongest oxidant and reductant species in an ionic solution
  • identified the majority of organic structures and reagents used in the given reaction scheme
  • drew structures that included the correct numbers of atoms and bonds
  • correctly calculated the ionic product of PbClusing the given solubility data
  • identified and explained the role of nitric acid
  • correctly identified the expected hydrolysis products
  • predicted the number of peaks and expected positions of those peaks in 13C NMR spectra of the hydrolysis products
  • recognised hydrolysis of an ester and correct reaction products
  • related particle interactions with water to observations for polar, non-polar, and ionic species
  • disregarded non-concordant titres correctly
  • carried out calculations for a back titration with minimal errors
  • correctly determined a limiting reagent with justification
  • used enthalpy data to determine enthalpy changes for the majority of the thermochemical calculation
  • identified a plausible reason for the variation in observed energy release

Other candidates

Candidates who were not awarded Scholarship commonly:

  • showed very poor, difficult-to-follow working in calculations
  • did not attempt all questions
  • could not carry out calculations, or make sense of questions that deviated from the standard level 2 or 3 NCEA examination approaches
  • could not communicate their ideas in enough detail or with enough clarity
  • were unable to complete aqueous calculations for acid and base solutions
  • could not identify enthalpy and entropy changes in unfamiliar contexts
  • did not show understanding of the links between subatomic particles and ionisation enthalpies
  • made generic statements about the ionisation energy trends across the periodic table
  • did not identify species present in an ionic solution
  • were unable to use standard electrode potentials to identify the strongest oxidant and reductant species in a mixture
  • did not give correct observations or equations for the electrolytic reactions
  • could not identify the missing reagents or functional group changes in the organic scheme
  • did not complete organic structures, or missed drawing in all hydrogen atoms
  • could not complete solubility calculations
  • did not understand the role of nitric acid in preventing the hydroxide precipitate from forming
  • hydrolysed the given structure in incorrect locations
  • could not predict the number or position of peaks in 13C NMR spectra of the hydrolysis products
  • attempted to explain variations in IR data instead of 13C NMR data
  • did not identify hydrolysis of an ester or the correct reaction products
  • could not discuss particle interactions between water molecules and polar, non-polar, and ionic species
  • incorrectly discussed sodium sulfate as the insoluble precipitate responsible for the given observations
  • used NaOH as the solvent species to account for particle interactions and the given observations
  • did not recognise that a concentrated NaOH aqueous solution contained water
  • could not complete a back titration calculation
  • rounded values early on in a calculation before finishing
  • could not use thermochemical data to determine an overall enthalpy change
  • could not use mass data in molar calculations or identify a limiting reagent
  • incorrectly described heat loss to the environment as the reason for variation in the observed energy release
  • did not use units to indicate the meaning of calculation values
  • made poor use of chemical terminology.

Subject page

 

Previous years' reports

2019 (PDF, 206KB)

2018 (PDF, 105KB)

2017 (PDF, 43KB)

2016 (PDF, 203KB)

 
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