HSC Chemistry Paper Answers (1 Viewer)

jazz519

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Multiple choice:

1. A (burette is technically most accurate since a 50mL measuring cylinder has differences of 1mL on the markings, while the burette has 0.1 mL differences). However, it is q1 so they might not be looking for such an in depth analysis (let me know what you guys think).''

2. D (copper has blue-green), can't be carbonate as only metal ions can give a colour in the flame test and barium gives apple green and calcium gives a brick red

3. A (alphabetically chloro must be in front of fluoro and it is a butane based molecule since there are 4 carbons, therefore considering the lowest addition across the molecule while obeying IUPAC rules gives 2-chloro-1-fluorobutane )

4. D (an open flame is dangerous since the molecules being reacted and the products are all flammable and volatile. Can't be A (stopper on the top) since that would cause an increase in pressure and cause the flask to shatter. Can't be B (concentrated h2so4) as that doesn't improve safety, only improves the reaction rate and yield. C (changing direction) already is fine since hot gases rise so need for that).

5. A (HSO4^-. satisfies amphiprtoic meaning can act as a base and acid through accepting and donating protons. B can't accept protons, C can't donate protons, D can't accept protons)

6. B (Np-239) (answer has to be neutron rich since it has been produced in a nuclear reactor, and above uranium since its transuranic)

7. (from matrix solutions since my paper was missing these)

https://imgur.com/a/twQzw

8. C (lead can be precipitated by chloride ions, while barium is not able to)

9.D (the black deposit is soot. Cant be A as that is complete combustion, cant be B as it doesn't contain soot in the products, can't be C as hydrogen gas is not a product of combustion )

10. B (in the dry cell zinc is the anode so y=negative and carbon rod is the cathode = x, in the lead-acid cell pb=anode (y=negative), pbo2 = cathode (x = positive)

11. D (S goes from 0 to 4+)

12. D (straight away can't be A or C as both still contain double bonds, and B shows polyethylene)

13. B (this question has nothing to do with the strength of the acid please note this as the neutralisation reactions when any of the reactants are strong in this case NaOH satisfying that the reaction will always go to completion regardless of if this NaOH reacts with a weak or strong acid. So all we have to do for this q is look for the one containing the most amount of ionisable hydrogen i.e. citric acid)

14. A (ineffective because HCl is a strong acid, a buffer must contain weak acid/base and its weak conjugate. If you were wondering why a strong acid can't form a buffer: buffers don’t form with a strong acid such as HCl and its conjugate Cl-
​relates to the dot-point of the conjugate acids and bases, as Cl- is an extremely weak conjugate base it is unable to react with water and thus there is no possibility of an equilibrium (buffering) reaction forming.)

15. B (https://imgur.com/gallery/ypSeV)

16. B (not directly in the equation but NaOH causes the depletion of the H2co3 through neutralisation and thus causes the equilibrium to shift right reducing co2 concentration and thus the gas pressure is reduced ) (can't be A as adding more CO2 does shift equilibrium right reducing gas moles i.e. pressure but remember that Le Chatelier's principle only minimises the change and doesn't complete counteract it. So in fact you are increasing pressure by adding more carbon dioxide. Can't be c as this will shift equilibrium left and increase the pressure. Can't be D as increasing temperature shifts equilibrium to the endothermic side (left) increases co2 gas and thus pressure)

17. C (https://imgur.com/gallery/pa7zr)

18. D (Y and Z on the same side of the equation and X is on there side since both Y and Z increase while X decreases and this is because the change that occurs is due to a change in pressre/volume (increase in volume) as all concentrations drop instantaneously together. By LCP the system will shift to the side with the most gas moles to compensate for the reduced pressure. So this side must be the Y and Z one as these go up in concentration. So summarising Y and Z on the same side, and the side with Y and Z must have more gas moles. Now consider the ratio concentration changes for molar ratios (i.e. they all go up/down by the same one unit displayed in answer D)

19. C (https://imgur.com/gallery/qzzgk)

20. C (https://imgur.com/gallery/kq7Y6)
 
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jazz519

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Short Answers:

21a) Many answers you can give here. Some for the troposphere include:
- Ozone is a harmful pollutant as it causes respiratory problems (even at low concentrations of 0.1ppm)
- is a powerful oxidising agent that damages plant and animal life
- It also reacts with hydrocarbons from automobile exhaust to form secondary organic pollutants such as aldehydes, acrolein and peroxyacyl nitrates (PANs).

Stratosphere include:
- forms a thin layer in stratosphere and filters out UV-C and UV-B which damages living tissue in mutations by absorbing them in the Chapman reactions, acting as a UV radiation shield

if you have space maybe include chemical equations: O2(g) + UV ⇒ 2 O.(g)
O.(g) + O2(g) ⇒ O3(g)
O3(g) ⇒ O.(g) + O2(g)

b) Some properties you could compare + descriptions:

Appearance
Oxygen is a colourless and odourless gas, while ozone is a pungent, pale blue gas. (probably not a great example to use in this more so a add on to a 3 or 4 marker that asks for multiple)

Density
Ozone has higher density due to dipole-dipole interactions, therefore when in liquid form its molecules can orient their dipoles to minimise charge and hence stack closer together.

Shape
Oxygen is a linear molecule and ozone is bent shaped to maximise space between electron pairs.

Boiling Point
+ Solubility
Boiling point is a direct measure of the intermolecular forces present. The dipoles within ozone do not cancel out in the bent molecule thus it is slightly polar. Hence can form dipole-dipole interactions and has higher dispersion forces than the non-polar oxygen. Hence, has higher boiling point and higher water solubility.

Reactivity
Ozone is more reactive than oxygen because it has a much lower bond energy than oxygen. This is because oxygen contains a double covalent bond, whereas in ozone the double bond and coordinate covalent bond, these cannot be distinguished between and thus resonate chemically and can be viewed as a 1.5 covalent bond.

(I personally would also draw the structures on the side of my answer to show a basis from where the properties come from)

c) Cl•(g) + O3(g) ⇒ ClO• + O2(g)

or I think you could include this net reaction for the whole ozone depletion : O3(g) + O•(g) ⇒ 2O2(g) (Put Cl^. on the arrow showng its a catalyst)
 
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jazz519

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22a) x-axis: zinc conc, y-axis: absorbance, title need to be included
graph shape something like this with a line of best fit

https://imgur.com/a/04Qig

b) abs1/ppm1 = abs2/ppm2

0.58abs gives 3.45ppm (from drawing dotted lines on the graph roughly they will probably allow from 3.4 to 3.5ppm)

Therefore, it is not safe, as its above 2.80ppm

23a) As oxidation occurs at the anode (zinc), gradually there will be an excess of positive ions (Zn^2+) here. Similarly, at the cathode (Ag) due to reduction there will be an excess of negative ions (No3^-)

Without a salt-bridge, this would cause an imbalance of positive and negative charges in the system and the redox reaction ceases.

The salt bridge’s purpose is to complete the circuit and allow the migration of ions (Cations from the salt bridge flow towards the cathode, while anions flow towards the anode) to maintain electrical neutrality in both half cells. It must be soluble, one example is KNO3.

b)https://imgur.com/gallery/k2jfY

24a)https://imgur.com/gallery/hNYjY

b) Basic Salts: this is produced when a STRONG base and a WEAK acid react.

Dissociation of Salt Produced: NaCH3COO(aq) → Na+(aq) + CH3COO-(aq)

The Na+ is an extremely weak conjugate acid as it came from a strong base NaOH. This means it is too weak to react with water.

The CH3COO- is a weak conjugate base as it came from a weak acid CH3COOH. However, it is not as weak as Na+ and thus is able to react with water. Since it is a base, water will act as an acid.

Reaction (Hydrolysed) With Water: CH3COO-(aq) + H2O(l) ⇌ CH3COOH(aq) + OH-(aq)

Thus as OH- is produced it is a basic salt solution

25) Cellulose formed from the reaction of beta glucose monomers, which form a 1,4 -glycosidic linkage, n C6H12O6 (aq) → (C6H10O5)n (s) + (n-1) H2O(l), is a condensation polymer, that is a potential source of petrochemicals such as ethene because of its 6 carbon glucose monomer unit structure.

Conversion process:
1. Cellulose to glucose: (hydrolysis) using cellulase enzyme - (C6H10O5)n(aq) + nH2O(l) → nC6H12O6(aq)

2. Glucose to 15% v/v ethanol: In the fermentation of glucose, yeast is initially added to mashed grain and water. Any oxygen present will be absorbed by the growing and reproducing yeast cells and the conditions change to anaerobic. Upon this occurring yeast will respire and break down the glucose to obtain energy and in the process forms ethanol as a product of cellular respiration, as well as carbon dioxide gas (C6H12O6(aq) → 2 C2H5OH(aq) + 2 CO2(g) - write the catalyst on the arrow). When ethanol concentration reaches 15% v/v, the yeast die and fermentation stops.

3.15% v/v to 100% v/v ethanol: Fractional distillation and molecular sieving are required

4. Ethanol to ethene: dehydration using concentrated sulfuric acid catalyst. It works by breaking the C-OH bond and C-H bonds, allowing for the formation of a double bond and water. It is also a powerful dehydrating agent. (c2h5oh(l) ---> C2h4(g)+H2O(l)-write the catalyst on the arrow)

5. Ethene to polyethylene:https://imgur.com/a/88e5n

26a) Reasons why it's a concern could be:
- Acid Rain: is formed when acidic oxides such as SO2 react with water molecules in the atmosphere to produce acidic solutions.
SO2 (g) + H2O (l) ⇋ H2SO3 (aq) or SO2 can be oxidised first to produce SO3 (So2 + 1/2O2--> So3),which forms sulphuric acid (So3 + H2O ----> H2SO4). Rainwater, snow and other forms of precipitation containing these acidic solutions fall to earth as acid rain.

Effects:
Erosion of limestone (CaCO3) structures CaCO3(s) + H2SO4(aq) → CO2(g) + CaSO4(aq) + H2O(l)
Acidification of waterways, leading to harm to marine animals → industries and environment affected.
It leaches essential metal nutrients from the soil → trace elements are important in biological processes.
Dissolves Al3+ ions from normally insoluble, non-toxic Al(OH)3 → toxic to plants, stunts root growth.

- Health Problems: Sulfur dioxide is a severe respiratory irritant and can cause breathing difficulties at concentrations of 1ppm. It can also trigger asthma attacks and aggravates conditions such as emphysema.

b) At the metal smelter: the extraction of metals from sulfide ores occurs as shown in the equation 3O2(g) + 2ZnS(s) → 2SO2 (g) + 2ZnO(s), this releases SO2 gas as shown in the black colour of the map portraying th high concentration of So2 above the metal smelter, as well as the dotted patches surrounding it showing the movement of the gas throughout the atmosphere.

Coal fire power stations: coal used in combustion is not completely pure and contains sulfur impurities which undergo combustion when the coal is burnt shown in S (s) + O2 (g) → SO2 (g) and this is displayed in the map in the black colour directly above the power station and dotted patches around it.

In the white areas: there is still some SO2 due to the movement of air molecules from the metal smelter and coal powered station, as well as due to natural causes such as volcanoes, geothermal springs and oxidation of H2S by bacteria (3O2(g)+ 2H2S(g) → 2SO2(g) + 2H2O(l)), however much less than the two other areas.

27) Firstly, acetic acid is an alkanoic acid, butan-1-ol is an alkanol and butyl acetate is an ester. I recommend drawing their structures to show the different intermolecular forces that can occur

Boiling point is a direct measure of the intermolecular forces present. So this suggests that although these molecules have different molar masses, that they have quiet similar amounts of intermolecular forces.

Firstly, the one with the lowest molar mass is acetic acid, it is a polar molecule as it contains a COOH group and a OH group and thus are able to form twice as many hydrogen bonds (the strongest intermolecular forces) between molecules, compared to the second highest molar mass (button-1-ol) since this molecule only contains one polar group being the OH.

The difference in the degree of hydrogen bonding in these two molecules explains why acetic acid has the lowest molar mass than the alkanol, and can also be used to explain why butyl acetate has the highest molar mass, as ester molecules which are polar are only able to form dipole-dipole interactions (both other molecules have this too) and are not able to form hydrogen bonds with other ester molecules.

To account for these differences in intermolecular forces that arise from the hydrogen bonding differences, the higher molar mass compounds (butanol and butyl acetate (this has higher molar mass) have higher dispersion forces than acetic acid (the electrostatic force of attraction between fluctuating dipoles in atoms and molecules) as this is directly proportional to molecular mass, allowing the molecules to all have relatively similar boiling points.

28a) Possible answers could be
Advantages:
- Theoretically carbon neutral:
Photosynthesis: 6CO2(g) + 6H2O(l) → 6O2(g) + C6H12O6(aq) (consumes 6 moles of CO2)
Fermentation of Glucose: C6H12O6(aq) → 2CO2(g) + 2C2H5OH(aq) (releases 2 moles of CO2)
Combustion: 2C2H5OH(l)+ 6O2(g) → 4CO2(g) + 6H2O(l) (releases 4 moles of CO2)
Thus, from these equations there is no net release of CO2. However, in reality it is not as fuels are burnt in fractional distillation prior to step 3 (required as fermentation only produces 15% v/v), during growth and harvesting and also during transportation of fuels, but it is still much more environmentally friendly than octane.

- It burns cleaner than octane: due to its shorter carbon chain length and the fact it already contains an oxygen atom, so less oxygen is required per mole of fuel. Therefore, it more readily undergoes complete combustion which reduces toxic pollutants such as C (soot - carcinogenic) and CO (binds irreversibly with hemoglobin in red blood cells, restricting oxygen leading to hypoxia) produced from incomplete combustion.

- Also increases fuel efficiency as heat of reaction given by ∆H = bonds broken - bonds formed, reduces in incomplete combustion as CO is less stable than CO2, so less bonds are formed and thus it is less exothermic.
Ethanol Complete Combustion: C2H5OH(l)+ 3O2(g) → 2CO2(g) + 3H2O(l)
Octane Complete Combustion: C8H18(l)+ 252O2(g) → 8CO2(g) + 9H2O(l)
Octane Incomplete Combustion: C8H18(l)+ 6O2(g) → CO2(g) + 6C(s) + CO(g) + 9H2O(l)

- Renewable if from plant matter: explain the starch to ethanol dot point

Disadvantages:
- Engine modifications: When more than 15% v/v of ethanol is used as an additive to regular petrol known as gasohol is used in car engines, expensive engine modifications are required as ethanol is a polar molecule and thus attracts water causing corrosion.

- Large areas of arable land are required to grow crops: which has an ethical issue in the use of crops for fuel and also large environmental problems such as soil erosion, deforestation and salinity issues.

- Lower molar heat of combustion: produces less energy per mole than octane, so this means that more fuel is needed for same energy (i.e. to travel the same distance).

- Disposing large amounts of waste fermentation liquors: after ethanol removal can be environmentally damaging.

b)https://imgur.com/gallery/jdoyG

29)

Turbidity: is a measure of the clarity of water due to suspended matter.
Site X has low amount since it is coming from the limestone caves (however there is still some because of the farm).

Site y has a very high amount due to particles from the saw mill entering the water system. However, these particles are large and can easily be removed through the sedimentation and flocculation process.

Problems with high turbidity:
Decreases penetration of sunlight, limiting photosynthesis (dissolved oxygen decreases)
Small particles in upper layers can absorb infrared light raising water temperature which can lead to thermal pollution and further reduces the dissolved oxygen content.
Particles can clog fish gills.

pH: the PH of X is higher than 7 due to the limestone, while pH of Y is 6 due to natural co2 equilibrium. However, this isn't that much of an issue, as the town has pH control.

Calcium: At site X there is a high calcium concentration as limestone contains Ca^2+ in the formula. A contributor to water hardness (a measurement of the concentration of divalent metal ions such as Ca2+ and Mg2+ in water expressed as equivalent amount of dissolved CaCO3). Site Y has relatively low levels. The high count at site X is a large problem as this may lead to blockages in houses, affects water taste and also prevents soaps from lathering (potentially increasing bacteria amounts in the water).

Phosphate:At site X there is a high phosphate concentration due to the manure from the cows containing fertilisers which have a high amount of phosphate. this is a problem as this can lead to eutrophication, the process where water becomes enriched with nutrients such as PO43- and NO3-, primarily from fertilisers and detergents, to an extent that it promotes the formation of algal blooms.

PO43- is generally considered to be the growth limiting agent, recommended levels of P:N are 1:10 with 0.01-0.ppm and 0.1-1ppm, respectively (Site Y is in this range)

Effects:
Eutrophication increases the BOD and reduces the dissolved oxygen, reducing survivability of aquatic organisms.
Increases turbidity
Forms a layer that prevents any photosynthesis from plants, which reduces dissolved oxygen content.
Cyanobacteria produce poisons that can kill livestock and cause diseases in humans.

Assessment: Site Y is a better source for the town's water as the problems with the initial water supply can all be solved through the water purification steps

30)A scaffold that could be used to answer the q:
Balanced chemical equation (with the exothermic nature indicated + catalyst on arrow ) N2 (g) + 3H2 (g) ⇋ 2NH3 (g) ΔH = - 92 kJ/mol
Discussion of the equation (i.e. in terms of the exothermic nature and position of equilibrium at normal room temperatures and pressures)

Source of the reactants:
N2 is sourced from fractional distillation of liquefied air
H2 from the electrolysis of H2O, but it is more commonly sourced from the reaction of steam and methane (CH4(g) + 2H2O(l) ⇒ CO2(g) + 4H2(g))

Why we need to manipulate conditions:
The Haber process is an exothermic equilibrium reaction and is therefore subject it is subject to Le Chatelier’s Principle (MUST DEFINE IT - When a system at equilibrium is disturbed, the system attains a new equilibrium by undergoing a chemical reaction which minimises the effect of the disturbance.) Due to this the reaction conditions must be manipulated in order to find a delicate balance between the rate of reaction as well as the yield of the reaction (crucial for an economically viable industrial process).

The strong covalent bonding between N2 and H2 atoms results in a high activation energy and thus at standard conditions causes the equilibrium to lie well to the left (i.e yield is very low).

Temperature:
Increase in temperature - increases reaction rate (describe why)
Increasing temperature speeds up the rate of reaction by providing kinetic energy through the conversion of thermal (heat) energy to kinetic energy increases to reactants and products, allowing more molecules to possess the correct collisional orientation and energy to overcome the EA (activation energy barrier) (therefore there is more successful collisions).

Increase in temperature - reduces yield (describe why in terms of LCP)
However, as the forward reaction is exothermic, increasing the temperature is a disturbance by Le Chatelier’s Principle. This causes the equilibrium to shift towards the endothermic reaction, the left, resulting in decomposition and decreases the yield of NH3.

Also, high temperatures are expensive to maintain and can damage the inorganic catalyst.

Compromise conditions
Therefore a compromise of 400-500℃ is used in conjunction with a heterogenous catalyst (Fe3O4).

Discussion of the use of the catalyst and what is done to it to enhance properties
Using a catalyst increases the rate of reaction by reducing the EA for the reaction by providing an alternate pathway (adsorption) for the reaction to occur, with a lower activation energy.
Thus allowing for a lower temperature to be used, which reduces the effects due to the use of higher temperatures which reduce the yield of ammonia.

The catalyst is finely grounded to produce a large surface area and thus this also further increases the rate of reaction. Additionally, adding potassium increases electron density and reactivity, while adding calcium allows magnetite to maintain its larger surface area.

Pressure:
Increase in pressure - increases the yield (describe why in terms of LCP)
According to LCP, increasing the pressure is a disturbance that will shift the equilibrium to the side with least gas moles, the right (LHS:RHS = 4:2), thus increasing the yield.

Increase in pressure - increases reaction rate (describe why)

It also has the added benefit of increasing rate of reaction as the concentration of reactants increases.


Disadvantages of this increase in pressure + compromise conditions
However, high pressures require expensive equipment and are dangerous to maintain and so a pressure of 250 atm is used.

3-4 Other Conditions important in monitoring:
The main monitoring required has been discussed in the above dot-points.

Other conditions also used include:
- A 1:3 mole ratio of N2 to H2 is used in line with the stoichiometric mole ratios.
- NH3 is removed via liquefaction, forcing the equilibrium right increasing yield.
- Unused reactants are recycled to save costs.
- Gases: no oxygen (system would become explosive), argon and methane (decreases efficiency) and CO which can poison catalyst.

Conclusion:
thus monitoring is essential to ensure efficiency, maximising yield, increasing rate of reaction and safety.
 
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jazz519

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Industrial Chemistry:
31ai) https://imgur.com/gallery/z5EH1

ii) 1. Add 20mL of olive oil and 20 mL 10M NaOH (concentrated) into a 100mL beaker
2. Heat with hot plate at 35 oC until no olive oil is visible and stir with a glass rod
3. Let mixture cool down and then add brine to precipitate the soap
4. Filter off the mixture with a buchner funnel. The Solid residue is soap
5. Wash soap with some water to remove trace alkali

Testing the soap:
1. Add 3 mL of tap water and 3 mL of hard water into 2 separate test tubes.
2. Add a small amount of the produced soap into each of the test tubes
3. Gently shake and record observations.

bi)https://imgur.com/a/tATir a steeper initially graph do to increase in reaction rate, but because of LCP, the yield is less as higher temperatures favour the endothermic (left) side so SO3 concentration will be lower

ii)https://imgur.com/gallery/YfNLx

ci) x= NaHCO3 (sodium hydrogen carbonate), y=CaO (calcium oxide)

ii)Brine purification: First, a 28% w/w solution of sodium chloride (brine) is prepared. Impurities (mainly Ca^2+, Mg^2+ and Fe^3+) are precipitated out by adding CO3^2- and OH^-.
Ca2+(aq) + CO32-(aq) → CaCO3(s)
Mg2+(aq) + 2OH-(aq) → Mg(OH)2(s)
Fe3+(aq) + 3OH-(aq) → Fe(OH)3(s)

iii)
The purified brine is then saturated with ammonia and sent to the Carbonation Tower: ammonia (weak base) reacts with carbonic acid (weak acid) to produce ammonium and hydrogen carbonate (bicarbonate) ions. NH3(aq)+ H2CO3(aq) ⇌ NH4+(aq) + HCO3-(aq)

Then Sodium ions react with bicarbonate ions to form sodium hydrogen carbonate. Na+(aq) + HCO3-(aq) ⇌ NaHCO3(s)

The base of the tower is cooled to maximise precipitation and the solution is filtered to remove the precipitate and the ammonium chloride is used to recycle the ammonia.

The full formulae equation for the carbonation reaction is:
NaCl(aq) + CO2(g) + NH3(g) + H2O(l) ⇌ NaHCO3(s) + NH4Cl(aq) ∆H = -158 kJ/mol

Ammonia recovery:
CaO from the kiln moves into the slaker which adds water to form Ca(OH)2. CaO(s)+ H2O(l)→ Ca(OH)2(aq)

The Ca(OH)2(aq) is then mixed with the NH4Cl(aq) filtrate. This unit operation liberates ammonia and creates calcium chloride as waste. Ca(OH)2(aq)+ 2NH4Cl(aq) → CaCl2(aq) + 2H2O(l) + 2NH3(g)

Overall Reaction for Solvay process: 2NaCl(aq) + CaCO3(s) → Na2CO3(s) + CaCl2(aq) ∆H = 20 kJ/mol, as shown in this ammonia isn't consumed in the reaction and is therefore a catalyst: speeds up rate of reaction by lowering activation energy, allowing more molecules to have the required collisional energy to overcome the activation energy barrier.

d) Before brine solutions can be used in any of the processes they must be purified. First, a 28% w/w solution of sodium chloride (brine) is prepared. Impurities (mainly Ca^2+, Mg^2+ and Fe^3+) are precipitated out by adding CO3^2- and OH^-.
Ca2+(aq) + CO32-(aq) → CaCO3(s)
Mg2+(aq) + 2OH-(aq) → Mg(OH)2(s)
Fe3+(aq) + 3OH-(aq) → Fe(OH)3(s)

Mercury Process:
Chemistry: the anode is a segmented titanium plate and the site of oxidation: 2Cl–(aq) → Cl2(g) + 2e–, while the cathode is mercury and the site of reduction: Na+(aq) + e- → Na(s).

Sodium dissolves in mercury to produce an amalgam which flows into the next area of the cell, where the sodium and water combine to form NaOH (2Na(l) + 2H2O(l) → 2NaOH(aq) + H2(g)).

The overall reaction in this process is: 2NaCl(aq) + 2H2O(l) → Cl2(g) + H2(g) + 2NaOH(aq)

Diagram: https://imgur.com/a/Fdxtt

Advantages:
Produces very pure NaOH as it avoids any interaction with chlorine gas and the amalgam.
Avoids using asbestos (carcinogenic)

Technical:
The mercury cell operates at the highest working voltage and thus the cost of the electricity needed is the greatest. It needs a large power source to supply a current of up to 10,000 amps to reduce Na+
Mercury is lost hence money is lost.

Environmental:
Although the mercury is recycled, there is still an unavoidable loss into the environment and cause harm as it’s a neurotoxin which poisons the nervous system and can cause brain damage. It does this through bioaccumulation within the food chain.
Also, chlorine gas is a strong oxidant which can combine to form substances known as dioxins which can pollute a waterway. This can cause cancer and skin diseases.
It results in large heat production which leads to thermal pollution (discussed in membrane part)

Diaphragm Process:
Chemistry: NaOH is produced by electrolysis of acidified brine using an inert titanium anode which is the oxidation site: 2Cl–(aq) → Cl2(g) + 2e– and a steel mesh cathode which is the reduction site: 2H2O(l) + 2e– → H2(g) + 2OH–(aq), separated by an asbestos diaphragm. The asbestos diaphragm is designed to let Na+ ions cross to meet the OH- ions which are produced at the cathode.

However, it also allows Cl- ions to cross, which means the NaOH is slightly contaminated.

The overall reaction in this process is: 2NaCl(aq) + 2H2O(l) → Cl2(g) + H2(g) + 2NaOH(aq)

Diagram:https://imgur.com/a/aKKnL

Advantages:
It produces large quantities of sodium hydroxide and chlorine, two high-demand industrial chemicals, at quite reasonable costs and levels of purity.

Technical:
The NaOH is not very pure (always has Cl-)

Environmental:
Asbestos is carcinogenic.
Hypochlorite (OCl-) a strong oxidant is produced in the waste brine solution.
Also, chlorine gas is a strong oxidant which can combine to form substances known as dioxins which can pollute a waterway. This can cause cancer and skin diseases.
It results in large heat production which leads to thermal pollution (discussed in membrane part)

Membrane Process:
Chemistry: This process is virtually identical to the diaphragm process. However, instead of an asbestos diaphragm it utilises a polytetrafluoroethylene (PTFE) membrane.

Diagram:https://imgur.com/a/YbWB9
Advantages:
Solves asbestos and mercury issue
Membrane only allows passage of Na and not Cl. Therefore, NaOH is purer than the diaphragm process
No OCl- in spent brine
Most energy efficient therefore reduces the amount of fossil fuels that must be burnt for the electricity (list some negatives of burning more fuels i.e. acid rain, global warming, photochemical smog)

Environmental:
Made from petrochemicals a non-renewable resource.
Also, chlorine gas is a strong oxidant which can combine to form substances known as dioxins which can pollute a waterway. This can cause cancer and skin diseases.
It results in large heat production which leads to thermal pollution (when discharged back into the environment can lead to thermal pollution. This is harmful as dissolved oxygen content decreases exponentially as temperature increases. This can thus lead to hypoxic zones in a river.)

Technical:
Requires very pure brine
More frequent replacement

Assessment: just summarise the above and state which one is better for environmental and industrial (i.e. membrane)
 
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trea99

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Based on the answers you've provided one of q7-9 was a question that asked something along the lines of "What is the density of ozone at 25degC, 100kPa?"
Answer - divide molar mass of ozone by molar volume (at RTP) and you get 48/24.79gL^-1 which is 1.936... option C
 

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pipette's which are normally used for transporting standard solution to flask have predetermined values so the mL difference wouldn't really matter... maybe idk just hoping its measuring cylinder and not burette
 

jazz519

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Based on the answers you've provided one of q7-9 was a question that asked something along the lines of "What is the density of ozone at 25degC, 100kPa?"
Answer - divide molar mass of ozone by molar volume (at RTP) and you get 48/24.79gL^-1 which is 1.936... option C
I think that was q17
 

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Question 7 was the hexene, hexane and bromine water...wasn't too sure on that. Is it miscible or immiscible?
 

ichila101

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Question 7 was diagrams of two test tubes for each choice in each diagram where you had to pick what would happen when bromine is added to water, I think the first option was the test tube with hexane was clear and the test tube with hexene was brown. The second was the same I think only with two immiscible layers, the third the colours where switched around but the same as the second picture and the fourth had clear hexene and brown hexane.
Also it was noted that it was in the absence of UV light

Question 8 was about checking what would precipitate with lead and the choices were:
A) sulfate
B) nitrate
C) chloride
D) carbonate

Question 9
Was about combustion
 

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Question 7 was diagrams of two test tubes for each choice in each diagram where you had to pick what would happen when bromine is added to water, I think the first option was the test tube with hexane was clear and the test tube with hexene was brown. The second was the same I think only with two immiscible layers, the third the colours where switched around but the same as the second picture and the fourth had clear hexene and brown hexane.
Also it was noted that it was in the absence of UV light

Question 8 was about checking what would precipitate with lead and the choices were:
A) sulfate
B) nitrate
C) chloride
D) carbonate

Question 9
Was about combustion
I believe Question 8 was along the lines of "Which of the following could be added to a solution to determine the presence of Ba^2+. The solution also contains Pb^2+ ions?" something like that, and for each of the 4 options you were adding the sodium salt.
Question 9 showed a spirit burner with some alkanol in it and said that black spots? formed on the bottom of the flask and the energy released measured was less than theoretical values. Which of the reactions below could account for these observations?
One of them was not an alkanol it was an alkane being combusted. The other three were alkanols but one of them was complete combustion, in another H2 was produced as a product and option D (what I put) had Carbon, CO2 and H2O as products.
 

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Hey Jazz with that question there was a scale on the diagram of like 2cm to 1000km. Do you think we needed to use that at all? (One about metal smelter and coal fired power station)
 

jazz519

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Hey Jazz with that question there was a scale on the diagram of like 2cm to 1000km. Do you think we needed to use that at all? (One about metal smelter and coal fired power station)
Don't really think so (maybe but I don't think its that necessary)
 

jazz519

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pipette's which are normally used for transporting standard solution to flask have predetermined values so the mL difference wouldn't really matter... maybe idk just hoping its measuring cylinder and not burette
that's true, but this isn't titration (we have water being transferred) and most pipettes in school are 25mL
 

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\I hope question 7's d and matrix is wrong bc option c had bromine water on top of the hydrocarbon but aren't hydrocarbons less dense than water? holy fuck if these answers are right im getting like 10/20 for multis LOL K.M.S.
 

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\I hope question 7's d and matrix is wrong bc option c had bromine water on top of the hydrocarbon but aren't hydrocarbons less dense than water? holy fuck if these answers are right im getting like 10/20 for multis LOL K.M.S.
IKR, the MC this year was hard. Short answers/long responses were okay/straightfoward
 

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