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HSC 2012-2015 Chemistry Marathon (archive) (2 Viewers)

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Ekman

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re: HSC Chemistry Marathon Archive

For industrial chem people:

Can someone explain to me why Water is reduced in the Concentrated NaCl.

In Ahmad Shah notes it says "A lower Eo value means the reaction is more likely to occur", however:

the Na one is (-2.71V), while the water one is (-0.83V). Here the lower Eo value is Na, but i know that water is reduced, not Na.
Is Ahmad Shah statement wrong? Is it meant to say, "A less negative Eo value means the reaction is more likely to occur"?
What he means by lower potential, he means that less energy is required to reduce water, hence it is favoured over reducing sodium.
 

Mr_Kap

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re: HSC Chemistry Marathon Archive

What he means by lower potential, he means that less energy is required to reduce water, hence it is favoured over reducing sodium.
Oh ok. :)
 

BlueGas

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re: HSC Chemistry Marathon Archive

Quick question, what should the units always be in when doing calculation questions, I know ml always has to be converted to litres how about mg/g/kg? What should that always be in?
 

rand_althor

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re: HSC Chemistry Marathon Archive

Quick question, what should the units always be in when doing calculation questions, I know ml always has to be converted to litres how about mg/g/kg? What should that always be in?
Usually grams.
 

Mr_Kap

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re: HSC Chemistry Marathon Archive

Quick question, what should the units always be in when doing calculation questions, I know ml always has to be converted to litres how about mg/g/kg? What should that always be in?
mass in grams.
volume, in litres.
energy in KiloJoules, (not so sure about this one.)
 

leehuan

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re: HSC Chemistry Marathon Archive

I find it weird how chemistry treats the gram as the fundamental unit for mass, whereas the kilogram is an S.I. base unit.
_________________________
NEXT QUESTION:

25g of anhydrous sodium carbonate is reacted with excess hydrochloric acid in a conical flask. A pipe was connected from the apparatus to a beaker filled with excess lime water. Assuming all of the gas reacted with the lime water, calculate the mass of calcium carbonate formed in the lime water.
 
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BlueGas

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re: HSC Chemistry Marathon Archive

I find it weird how chemistry treats the gram as the fundamental unit for mass, whereas the kilogram is an S.I. base unit.
_________________________
NEXT QUESTION:

25g of sodium carbonate is reacted with excess hydrochloric acid in a conical flask. A pipe was connected from the apparatus to a beaker filled with excess lime water. Assuming all of the gas reacted with the lime water, calculate the mass of calcium carbonate formed in the lime water.
Are these the steps in order to find the answer?

- Calculate the number of moles of sodium carbonate
- It's a 1:1 (sodium carbonate:carbon dioxide) ratio so number of moles of sodium carbonate = number of moles of carbon dioxide
- Reaction of CO2 with Ca(OH)2 forms calcium carbonate, also a one to one ratio for all reactants and products, so number of moles of carbon dioxide = number of moles of calcium carbonate
- Convert moles to mass

Is this right?
 

leehuan

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re: HSC Chemistry Marathon Archive

Pretty much yep correct method. In the exam you should of course write the actual equations out as well.
__________________________________
NEXT QUESTION:
Explain how transuranic elements can be produced including one example of a recently discovered element. (4)
 

BlueGas

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Pretty much yep correct method. In the exam you should of course write the actual equations out as well.
__________________________________
NEXT QUESTION:
Explain how transuranic elements can be produced including one example of a recently discovered element. (4)
Transuranic elements are synthetic elements with an atomic number larger than 92. They can be produced in two ways: Neutron bombardment in a nuclear reactor and particle acceleration. In nuclear reactors, atoms are bombarded with neutrons to produce an isotope which is unstable and undergoes beta decay, as a result a transuranic element is created. Particle acceleration occurs when a charged beams of ions are accelerated at high speeds to penetrate a target nucleus and a transuranic element is created. An example of a recently discovered element is Ununhexium, element 116 which was synthesised in December, 2000, by the Joint Institute for Nuclear Research (Dubna, Russia).
 

leehuan

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Transuranic elements are synthetic elements with an atomic number larger than 92. They can be produced in two ways: Neutron bombardment in a nuclear reactor and particle acceleration. In nuclear reactors, atoms are bombarded with neutrons to produce an isotope which is unstable and undergoes beta decay, as a result a transuranic element is created. Particle acceleration occurs when a charged beams of ions are accelerated at high speeds to penetrate a target nucleus and a transuranic element is created. An example of a recently discovered element is Ununhexium, element 116 which was synthesised in December, 2000, by the Joint Institute for Nuclear Research (Dubna, Russia).
Perhaps for a 4 marker you may be able to scrape it. 3 marks are definitely there. I was going to make it a 5 marker but I decided to tone it back down a bit. I would've liked to see one nuclear equation even though the question doesn't specifically ask for it.
 

BlueGas

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Perhaps for a 4 marker you may be able to scrape it. 3 marks are definitely there. I was going to make it a 5 marker but I decided to tone it back down a bit. I would've liked to see one nuclear equation even though the question doesn't specifically ask for it.
Why am I never able to get full marks lol. Is it because I didn't include an equation I lost that one mark?
 

leehuan

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Why am I never able to get full marks lol. Is it because I didn't include an equation I lost that one mark?
you may be able to scrape it.
But the band 6 response tries to incorporate everything they know if its relevant. E.g. if it's equilibrium principles Le Chatelier always pops up. Talking about the potentials of ethanol as an alternate fuel could include the combustion equation for ethanol and the delta H value, as well as that for octane, so you can compare heat per mole and realise that octane produces more energy.
 

BlueGas

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But the band 6 response tries to incorporate everything they know if its relevant. E.g. if it's equilibrium principles Le Chatelier always pops up. Talking about the potentials of ethanol as an alternate fuel could include the combustion equation for ethanol and the delta H value, as well as that for octane, so you can compare heat per mole and realise that octane produces more energy.
Okay, you mind posting up more questions?
 

leehuan

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Since everyone seems to be doing industrial.......

NEXT QUESTION:
Relate the properties of detergents to their applications and assess any environmental concerns associated with them. (6)
 

BlueGas

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Since everyone seems to be doing industrial.......

NEXT QUESTION:
Relate the properties of detergents to their applications and assess any environmental concerns associated with them. (6)
There are different types of synthetic detergents: Anionic, Cationic and Non-ionic, each of them are similar in structure as they have a non-polar hydrocarbon chain, however they are composed of different polar ends. Anionic detergents have a benzene sulphonate, which is negative and allows them to bind strongly to negative surfaces, hence why they are used as hair conditioners and fabric softeners. They are not used as hair shampoos as they strip too much oil from the hair. Cationic detergents have an ammonium group which is positive and are used as hair shampoos as they produce a fair amount of foam compared to anionic and non-ionic, hence why they are not used as front-loading washing machine detergents. Instead, non-ionic, which have a hydroxyl group are used as they don't produce a lot of foam. Early detergents were non-linear (branched) and were non-biodegradable, so they had an environmental impact. Detergents also use builders which increase their efficiency as cleaning agents, however this led to eutrophication to due increase in phosphate levels. Today's detergents are linear (unbranched) so they are biodegradable with very minimal environmental issues.
 

Mathsisfun15

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re: HSC Chemistry Marathon Archive

Since everyone seems to be doing industrial.......

NEXT QUESTION:
Relate the properties of detergents to their applications and assess any environmental concerns associated with them. (6)
They wont do that this year as they had a 7 marker on it last year
 

Mathsisfun15

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Pretty much yep correct method. In the exam you should of course write the actual equations out as well.
__________________________________
NEXT QUESTION:
Explain how transuranic elements can be produced including one example of a recently discovered element. (4)
Is that even in the syllabus? I've never seen a question like that before
 

leehuan

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They wont do that this year as they had a 7 marker on it last year
Admittedly, I just did the 2014 paper casually without considering what the questions actually were and their unlikelihood of appearing this year. But it's still good practice, in case a 3 marker on just the structure comes up or something etc.

Other quote -
describe how transuranic elements
are produced
+
process information from secondary
sources to describe recent
discoveries of elements
 

leehuan

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There are different types of synthetic detergents: Anionic, Cationic and Non-ionic, each of them are similar in structure as they have a non-polar hydrocarbon chain, however they are composed of different polar ends. Anionic detergents have a benzene sulphonate, which is negative and allows them to bind strongly to negative surfaces, hence why they are used as hair conditioners and fabric softeners. They are not used as hair shampoos as they strip too much oil from the hair. Cationic detergents have an ammonium group which is positive and are used as hair shampoos as they produce a fair amount of foam compared to anionic and non-ionic, hence why they are not used as front-loading washing machine detergents. Instead, non-ionic, which have a hydroxyl group are used as they don't produce a lot of foam. Early detergents were non-linear (branched) and were non-biodegradable, so they had an environmental impact. Detergents also use builders which increase their efficiency as cleaning agents, however this led to eutrophication to due increase in phosphate levels. Today's detergents are linear (unbranched) so they are biodegradable with very minimal environmental issues.
Have to deduct marks for incorrect evidence here... 4
Check if you have anionic and cationic mixed up on applications. Non-ionic looks good (although if you can relate the ethoxy group it would be better). I believe environment was addressed well.
 

Fizzy_Cyst

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re: HSC Chemistry Marathon Archive

New Question: (kudos to addoil) [4 marks]

A student titrated 0.14 M barium hydroxide solution with 22.35mLs of 0.08M nitric acid to the equivalence point.

The student accidentally spilt an excess 13.5mL of barium hydroxide into the mixture.

Calculate the pH of the resulting solution.
 
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