Chemistry 2018 HSC exam pack (archive)

Students should:

• use the number of lines as an indication of the expected length of the response
• address the key words with coherence and logical thinking
• directly answer all parts of the question
• use applied examples with specific details
• write legibly using a black pen
• indicate the question being answered if using additional booklets.

Question 21

In better responses, students were able to:

• draw a correct structure and show all atoms correctly placed on the monomer.

Areas for students to improve include:

• showing a monomer unit has a double bond.

Question 22

In better responses, students were able to:

• construct a clear sequence of steps based on solubility rules
• construct balanced ionic equations, with appropriate states
• explicitly state expected observations and subsequent conclusions.

Areas for students to improve include:

• understanding why a series of precipitation reactions may be in a particular sequence
• recalling the colours of common precipitates.

Question 23

In better responses, students were able to:

• correctly draw reactant and products
• demonstrate use of the terms volatile and flammable correctly
• explain conditions that increase both yield and safety
• link the conditions using Le Chatelier's principle in order to maximise yield.

Question 24

In better responses, students were able to:

• write a correctly balanced equation for fermentation
• show sequential steps in the calculation and all working with units.

Question 25

In better responses, students were able to:

• incorporate details from the graph in the explanation
• demonstrate an understanding of kinetic theory.

Areas for students to improve include:

• using formulas and balanced equations for common reactions
• explaining temperature change on an equilibrium system.

Question 26

In better responses, students were able to:

• relate the implications for society as a whole, rather than individuals in society
• relate the specific properties of their selected isotope to the use of the isotope
• articulate the advantages and disadvantages associated with the use of their selected isotope.

Question 27

In better responses, students were able to:

• correctly identify 2-chloro-1,1-difluorethane
• relate properties and implications of both CFCs and HCFCs, to the structure and composition of the atmosphere, as well as make an assessment of the relative merits of both.

Areas for students to improve include:

• correctly numbering the location of halogens
• using prefixes to identify the number of individual halogens in the molecule
• employing correct naming protocols
• ordering halogens alphabetically
• relating the presence or absence of the C-H bond to the stability of CFCs and HCFCs in the troposphere
• identifying molecules as HCFCs.

Question 28

In better responses, students were able to:

• demonstrate clear, sequential working for calculations
• apply graphing conventions correctly (plots, scale, axis, line of best fit)
• read from a graph.

Question 29

In better responses, students were able to:

• clearly link a property of sodium carbonate to explain its use as a standard solution
• perform titration calculations correctly to 4 significant figures showing correct steps  
• understand the suitability of indicators in titrations   
• clearly identify the titration would require less HCl to reach endpoint when using an indicator suited to a basic range  
• explain that less volume of HCl in the titre would result in a higher calculated concentration of HCl.

Areas for students to improve include:

• using appropriate formulae that are relevant to titration calculations    
• recognising that some substance absorb moisture from the air to gain mass, making them unsuitable as a primary standard  
• selecting and average titre values appropriately
• identifying the correct molar ratio of reactants.

Question 30

In better responses, students were able to:

• clearly explain the impact of temperature and carbon dioxide concentration on the equilibrium in terms of Le Chateliers Principle
• link the increase CO₂ to fossil fuel burning and linked the increased temperatures to increased CO₂
• analyse the competing equilibrium shifts to explain why ocean CO₂ levels were increasing.

Question 31

In better responses, students were able to:

• write a plan to assist in structuring a long response, using relevant scientific terminology and avoid the use of colloquial terms
• draw a soap molecule showing a nonpolar/hydrophobic hydrocarbon tail and a polar/hydrophilic, negatively changed head
• draw and label the sodium salt of a long chain fatty acid with both carboxylate and sodium ions in part
• explain the cleaning action of soap in terms of intermolecular forces using terms such as dipole-dipole or hydrogen bonding to describe the interaction between the polar/ hydrophilic end of the soap molecule with water and dispersion forces between the nonpolar hydrocarbon chain and grease or oil
• draw labelled diagrams of the various steps in this process
• clearly correlate a property of sulphuric acid to its transport and storage
• clearly provide reasons for the observations in first hand investigations
• correctly understands shifts on equilibrium according to Le Chateliers Principle
• correctly calculate a K expression using an ICE table
• address all environmental issues associated with the production of sodium hydroxide and sodium carbonate.

Question 32

In better responses, students were able to:

• write a plan to assist in structuring a long response, using relevant scientific terminology and avoid the use of colloquial terms
• write and balance equations including appropriate data from the data sheet
• relate deep ocean anoxic conditions to the action of sulfate reducing bacteria and provide the correct half equation for the reduction of SO₄^2- plus water to HS^- plus OH
• provide the correct half equation for oxidation of iron
• combine the products of these half equations to describe the formation of solid iron(II) sulphide and iron(II)hydroxide
• provide correct electrodes and electrolytes and describe the associated electrolytic and/or galvanic chemistry and utilise electrolytic and/or galvanic cell diagrams to support their explanations
• acknowledge that Ag₂S is an insoluble salt and cannot be leached away
• provide clear links between advances in chemistry and methods used to prevent corrosion of steel ships
• correctly attribute the scientist and/or development in chemistry with appropriate corrosion prevention method
• provide a range of relevant protection methods and explain the underlying chemistry and provide relevant chemical equations.

Question 33

In better responses, students were able to:

• write a plan to assist in structuring a long response, using relevant scientific terminology and avoid the use of colloquial terms
• specify stage and location of cellular respiration
• link glcolysis to formation of 2 pyruvate, net 2 ATP and 2 NADH
• draw correct structural formation with specific attention to bond connections
• relate bonds and forces to how they affect protein shape and utilizing diagrams to advantage
• link α– (1,4) and α– (1,6) glucose linkages to branching in glycogen
• understand how to calculate ∆H and use this value, along with correct, balanced equation to determine correct decision
• correctly identify muscle types linking them to their structure, number of contractile fibres, type of activity and contractile process
• provide detailed explanation of contractile process and correctly links types to activity and structure.

Question 34

In better responses, students were able to:

• write a plan to assist in structuring a long response, using relevant scientific terminology and avoid the use of colloquial terms
• apply Hund’s rule to draw the orbital configuration of the sodium element
• explain that electron filling should follows the Aufbau’s principle
• outline an investigative method for testing the oxidation strength potassium permanganate and clearly show the independent, dependent and control variables
• distinguish the difference and similarities between absorption and emission spectra
• show both UV and IR absorption spectroscopy and reflectography in the form of instrumentation, printouts of the functional group bands and absorbance peak and the interpretation of the printouts in terms of chemical identification and concentration
• understand at least two ancient cultures such as Aboriginal and Ancient Egyptian and how they differ in terms of finding, grinding, purification of the pigments and combining with a medium and binder and also how paints are attached (spurting, hand smearing, using tools (woods, animal hair and brushes) to the surface such as rock, human skin and wood.

Question 35

In better responses, students were able to:

• write a plan to assist in structuring a long response, using relevant scientific terminology and avoid the use of colloquial terms
• identify the function of a specific part of a Mass Spectrometer and identify some advantages of Mass Spectrometry
• understand the structural differences between reducing and non-reducing sugars and the reagent used to distinguish them
• identify that everyone's DNA is different
• identify some features of AES and Chromatography.