HSC Chemistry Question Thread

[hanaacdr]

Hi
I was wondering what the fermentation of glucose diagram looks like?
thanks

[Natasha.97]

Hi
I was wondering what the fermentation of glucose diagram looks like?
thanks

Hi!

Definition: Breakdown of glucose by yeast to form ethanol and carbon dioxide.
Equation: C₆H₁₂O_6(aq) → C₂H₅OH_(l)+2CO_2(g)

The cotton wool prevents any oxygen from entering the conical flask, thus causing the yeast to respire and produce ethanol.



The mixture produced contains ~15% alcohol (yeast cannot tolerate higher concentrations). Distillation is required to produce high concentrations of ethanol.

In case you need the diagram for distillation:


Hope this helps!

[ilovemycat]

Hi everyone. I was doing a james ruse past paper for chemistry and i got this question wrong, and im not sure why.can someone help me please?

A mixture of oil, salt, sawdust and water are to be separated into their individual
components, each component being collected separately. What sequence of steps should
be followed to do this separation and collection?
(A) decantation filtration  separating funnel  evaporation
(B) filtration  separating funnel  distillation
(C) fractional distillation filtration  decantation
(D) filtration  separating funnel evaporation

[MisterNeo]

Hi everyone. I was doing a james ruse past paper for chemistry and i got this question wrong, and im not sure why.can someone help me please?

A mixture of oil, salt, sawdust and water are to be separated into their individual
components, each component being collected separately. What sequence of steps should
be followed to do this separation and collection?
(A) decantation filtration  separating funnel  evaporation
(B) filtration  separating funnel  distillation
(C) fractional distillation filtration  decantation
(D) filtration  separating funnel evaporation

What was the answer?
I think it would be B.
It can't be A or D because evaporation doesn't allow collection of water like the question says.

[jakesilove]

Hi everyone. I was doing a james ruse past paper for chemistry and i got this question wrong, and im not sure why.can someone help me please?

A mixture of oil, salt, sawdust and water are to be separated into their individual
components, each component being collected separately. What sequence of steps should
be followed to do this separation and collection?
(A) decantation filtration  separating funnel  evaporation
(B) filtration  separating funnel  distillation
(C) fractional distillation filtration  decantation
(D) filtration  separating funnel evaporation

I suspect it would have to be B, right? The only use of decanting would be to separate the water from the oil. However, if you've already used fractional distillation, you would have separated these components! So, I don't think C makes sense

[bsdfjnlkasn]

Hey there!

I was just wondering what the best way to prepare for the HSC Chemistry exam was? Which schools have the 'best' papers and until which year of the HSC should we go back to?

Should we be doing anything extra? Apart from learning and possibly rewriting summaries?

Any advice would be super appreciated!!

[Natasha.97]

Hey there!

I was just wondering what the best way to prepare for the HSC Chemistry exam was? Which schools have the 'best' papers and until which year of the HSC should we go back to?

Should we be doing anything extra? Apart from learning and possibly rewriting summaries?

Any advice would be super appreciated!!

Hi!

Doing past papers are the best way to prepare imo. That way, you get more exposure to the style of questions that may be asked. In addition to checking your work with the marking criteria, also take a look at the Notes from the Marking Centre to see the areas of weaknesses that particular cohort had in terms of answering questions.

In terms of HSC/trial papers, I'd prioritise doing HSC papers, and if I run out of HSC, I'd do trial papers from selective schools e.g. JRAH/Sydney Girls + Boys etc. Not too sure about how many years to go back in terms of papers though.

In terms of studying, try and incorporate different techniques to retain information e.g. mind-maps, flashcards, notes around the house (formulas/equations), recording yourself etc. The key thing is to maintain a balance () between studying and relaxing: make a study timetable from the moment you wake up to the moment you go to bed (more info on that here)

Hope this helps!

[justwannawish]

A couple of prelim qs:

1) If the question doesn't specify, how do you know the states of the products and reactants? Are there any other general hitns like how everything in solution is aqueous?
2) What are the most important (I know it's a subjective) concepts for prelim? Our teacher has been focusing most of our revision on molar calculations, limiting reagents, concentration, enthalpy but are there any other ideas that usually come up in prelim yearlies?

Thank you!

[Natasha.97]

A couple of prelim qs:

1) If the question doesn't specify, how do you know the states of the products and reactants? Are there any other general hinTs like how everything in solution is aqueous?
2) What are the most important (I know it's a subjective) concepts for prelim? Our teacher has been focusing most of our revision on molar calculations, limiting reagents, concentration, enthalpy but are there any other ideas that usually come up in prelim yearlies?

Thank you!

Hi!

Not too sure about the first question, sorry!

- Separating a variety of mixtures
- Intermolecular(dispersion/dipole-dipole/hydrogen) and Intramolecular(ionic/covalent/metallic) forces
- Development of the Periodic Table
- SOLUBILITY OF SALTS
- Diamond/Graphite comparison

Hope this helps!

[winstondarmawan]

Hello!
So this is not a traditional question, but for my trial exams I received 3/4 for a question (Shipwrecks Option Topic). It was something along the lines of:
Account for the presence of certain bacteria in deep sea wrecks, and using relevant equations explain their effect on the corrosion of such wrecks (4)
The reason why I lost a mark was because the teacher's marking criteria said that 1 mark was allocated to the anode reaction and 1 mark to the cathode reaction.
However, I had written the overall reaction (net reaction) and had received 1 mark only. I queried with my class teacher and she said that my overall reaction was counted as the cathode reaction () and she was adamant about me not receiving the mark.
My main gripe with this is because the question did not specifiy that the REDOX HALF EQUATIONS were required, but just RELEVANT EQUATIONS which was what my response had.
Is this worth pursuing with the head teacher? Would appreciate any opinions/advice on this matter, even if you don't/haven't done Shipwrecks or have had any similar experiences.
Thanks in advance.

[Natasha.97]

Hello!
So this is not a traditional question, but for my trial exams I received 3/4 for a question (Shipwrecks Option Topic). It was something along the lines of:
Account for the presence of certain bacteria in deep sea wrecks, and using relevant equations explain their effect on the corrosion of such wrecks (4)
The reason why I lost a mark was because the teacher's marking criteria said that 1 mark was allocated to the anode reaction and 1 mark to the cathode reaction.
However, I had written the overall reaction (net reaction) and had received 1 mark only. I queried with my class teacher and she said that my overall reaction was counted as the cathode reaction () and she was adamant about me not receiving the mark.
My main gripe with this is because the question did not specify that the REDOX HALF EQUATIONS were required, but just RELEVANT EQUATIONS which was what my response had.
Is this worth pursuing with the head teacher? Would appreciate any opinions/advice on this matter, even if you don't/haven't done Shipwrecks or have had any similar experiences.
Thanks in advance.

hmm.

My interpretation of the question is that you need equations (emphasis on the plural), so I think you lost a mark as you had put one equation instead of two

[winstondarmawan]

hmm.

My interpretation of the question is that you need equations (emphasis on the plural), so I think you lost a mark as you had put one equation instead of two

I had another 2 equations for the formation of rusticles.
EDIT: The criteria was as follows:
1 - Explain the presence of anaerobic bacteria
2 - Cathode reaction
3 - Anode reaction
4 - Explains formation of rusticles (with relevant equations)
Wouldn't the overall reaction count as both anode and cathode?

[Natasha.97]

I had another 2 equations for the formation of rusticles.

In that case, I'm not so sure. sorry!

Edit: Normally for anode/cathode reactions, the electrons are shown. Net Ionic Equations don't show them (or at least the ones I've seen), so maybe there needs to be clarification of which species is accepting/giving electrons

[Mathew587]

Can someone pls explain why for q 12 2015 hsc the answer is a and not d?

[A TART]

Can someone pls explain why for q 12 2015 hsc the answer is a and not d?

The number of neutrons (not protons) have changed from Pu239 to Pu241 (If it was d, it would no longer be Pu, it'll be some other element)