EXAM QS

Question 1

is the experimental method valid?

2019 VCAA 5b

Answer 1

• The method is valid as data is consistent for standard solutions of different concentrations
  made up from pure sucrose.
• The conditions used in the HPLC were consistent across all the standards and the soft drink
  solution.
• Peak areas for the standard solutions and the diluted soft drink sample were recorded at the
  same retention time (of sucrose).
• The method is invalid because not enough points were established from zero glucose through
  to 0.80 g L–1 glucose.

Question 2

fators that would limit the life of the zinc-cerium cell

VCAA 2018 7f

Answer 2

loss/breakdown/oxidation/corrosion of the Zn electrode
* side reactions at the electrodes
* electrolysis of water during recharging
* (-) 2H+
(aq) + 2e– → H2(g) ; (+) 2H2O(l) → O2(g) + 4H+
(aq) + 4e–
* significant temperature change
* build-up of gases around electrode.

Question 3

which chemical analysis is most useful in determining whether a compound has a stereoisomer

VCAA 2019 MCQ12

Answer 3

NMR - peak area and splitting patterns are diff

misconception - chose infrared bc uv light causes clockwise /anticlockwise BUT infrared is infrared radiation

Question 4

one factor that would limit life of ZINC cerium cell

2019 VCAA Q7f

Answer 4

• corrosion of ZN electrode
• side reactions at electrode

Question 5

safety risk w chemical in experiment

2019 VCAA 9bi

Answer 5

• products that form
• hydrogen gas is flammable
• ensure no ignition sources are present

Question 6

state change to experimental design do they can achieve their aim of measuring current efficiency

2019 VCAA 9G

Answer 6

• use higher or borader range of NaCl
• hi8gher conc most likely to prouce chlrine gas
• 2 diff oxidation reactions occurring

Question 7

aspects of electrolysis experiment included in discussion section

2019 VCAA 9h

Answer 7

whether the data supports or refutes the aim/hypothesis
* comparison of expected to actual results
* analysis experimental design and errors
* relating to earlier work/theory (e.g. electrochemical series and its use in predicting electrode
half-equations).

Question 8

potential safety hazards of MG-NA hybrid cell

2021 vcaa 2b

Answer 8

• battery may overheat
• Mg relatively reactive so may react in body
• leakage of products/reactants

Question 9

amylose and cellulose similarities and differences in structure

2021 vcaa 3e

Answer 9

• glucose monomers
• straight chain unbranched polmers
• glycosidic links
• difference: CH2Oh group in amulose remains on same side of polymer
• in cellulose it alternates
• alpha glucose for amylose and beta glucose for cellulose

Question 10

explain why potassium bromide or potassium iodide could not replace KCL as electrolyte to produce KOH

Answer 10

KI as electrolyte would produce I2(s) which would contaminate the solution / react with OH-
 KBr as electrolyte would produce Br2(l) which would contaminate the solution / react with
OH-
 Using KCl leads to production of Cl2(g) which would bubble off from the solution

Question 11

evaluate the env impact of reacting methane w water and the electrolysis of water

Answer 11

Method 1 – impact depends on the source of methane
 If the source of CH4 is biogas generated from waste, the environmental impact is low
because CO2 is a less harmful greenhouse gas than methane.
 If the source of methane is fossil-fuel-based (or high temperatures are generated using
fossil fuels) the environmental impact is significant because CO2 produced adds to overall
greenhouse gas levels.
Method 2 – impact depends on source of electrical energy

 If the electrical energy source is renewable (e.g. wind/solar/hydro), there is no
environmental impact because no CO2 is produced.
 If the electrical energy source is coal or gas, the environmental impact is significant
because CO2 produced during combustion of the fossil fuel adds to overall greenhouse
gas levels

Question 12

reversible vs irreversible reactions

Answer 12

reversible reaction, there is continuous interconversion between the chemicals on either side of the reaction equation.
In anirreversible reaction, the reactants are converted to products, but the products cannot be converted back to reactants.

Question 13

explain what happens when an enzyme catalyses the hydrolysis of a protein

Answer 13

• enzyme allows access to active site for protein via lock and key
• enzyme binds the protein (substrate) to the active site so the peptide links react with water(hydrolyses)
• enzyme lowers Ea for hydrolysis of peptide links or acts as a catalyst for hydrolysis of peptide links
• enzyme retains shape after reaction.

Question 14

the oxidation of wich chemical is the primary carbohydrate source

Answer 14

• glucose is oxidised
• glycerol is hydrolysed to glucose first

Question 15

calibration graphs

Answer 15

• if there is a bump when heating stops but then it stabilises, you take the stabilised value as it means the calorimeter is insulated
• the stirring makes the temp more even

Question 16

semistructural formula

Answer 16

• if there is a central carbon and four groups attached to it that aren’t hydrogens
• write it as C (CH3)3Cl etc…

Question 17

energy efficiency

Answer 17

• energy released in a 55% energy efficient calorimeter
• means u have to divide by .55 to find the actual amount fo energy released by combustion

Question 18

determine whether same quanitty of gas is produced at each anode

2024 sample q6

Answer 18

• no. electrons entering and exiting the cell are equal
• the current/passage of electrons is consistent throutout the circuit
• the mole of electrong flowing to each anode is equal

Question 19

use integration curves to verify a peak has 2 equivalent H

Answer 19

• specify the ratio of the curves
• integration curve is double the height etc….

Question 20

why is an aq solution of CuSO4 used as the electrolyte

Answer 20

Cu2+ migrates to the cathode where reduction occurs as Cu2+ is the strongest oxidant.
The migration of Cu2+ to the cathode (-) and sulfate ions to the anode (+) prevents the build-up of charge at
each electrode.
Copper (II) sulfate contains Cu2+(aq), which is involved in the two half-reactions, and sulfate ions which do
not react under the reaction conditions.

Question 21

identify and explain one factor that may affect the useful life of Na-S test cell

Answer 21

• If discharge product is not in contact with the electrode battery life/efficiency is reduced because the
  battery cannot be recharged, and reactions cannot be reversed.
• Side reactions reduce the efficiency of the cell by reducing the amount of useful product that can be
  recharged.
• High temperatures increase the possibility of increasing side reactions.
• Low temperatures increase the possibility of crystallisation

Question 22

effect of temp on viscosity

Answer 22

As temperature increases, the viscosity decreases / time decreases.
At higher temperatures, the average kinetic energy of the molecules is higher. This increases the frequency
of collisions between molecules and weakens the intermolecular forces, causing lower viscosity.

Question 23

why do the two half cells need to be separated

Answer 23

• The half-cells need to be separated so that electrons can travel between the two half-cells in connecting wires (through the load) and the electrical energy harnessed.
• The bacteria are anaerobic, and the oxygen needs to be excluded from the oxidation half-cell; if the half-cells are not separated, electricity will not be produced.
• If there was no separation of the two half-cells, oxidation and reduction would occur together and electrons would not move through the external circuit.

Question 24

give one reason why the moderate intake of fat is necessary

Answer 24

• provides essential fatty acids that the body can’t produce

Question 25

types of enzyme catalysed chemical reactions involving proline in the human body

Answer 25

• undergo condensation reactions to form proteins/enzymes
• be formed from hydrolysis reactions of proteins/enzymes
• undergo oxidation reactions as it is broken down into smaller molecules

Question 26

how the polarity of the electrodes is established during recharge to allow the recharge to occur

Answer 26

• the recognition that the electrode polarity does not change when the system is changed from discharge to recharge. The relative reductive and oxidative strength of the chemicals present in the galvanic cell is what determines the polarity, and this is fixed for both the discharge and recharge processes.
• the recognition that the external power source causes the process to change at each electrode. This means that during the recharge the positive electrode becomes the anode and oxidation occurs here. This reversal of processes means that the original chemicals can be re-formed and hence the cell is recharged.

Question 27

how does the increase in temp affect the value of the equilibirum constant (exothermic reaction)

4 marks

Answer 27

• stating that the equilibrium constant decreases.
• recognising that the forward reaction is exothermic or the back reaction is endothermic.
• establishing that the increase in temperature causes the system to partially oppose this stress by causing a shift in the reverse direction, or by stating that the increase in temperature increases the rate of the back reaction more than the rate of the forward reaction.
• establishing that the [reactants] increases and the [products] decreases.

have to say both conc of reactants and products change and state the changes