HSC Chemistry Question Thread

[jakesilove]

Hiya,
For question B), why is the answer calculating the percentage of CO2 in the dry ice? Since it's asking for the purity, don't we find the mass of ice then find the percentage of that?
(Image removed from quote.)
Thanks.

Dry ice IS Carbon dioxide. So, finding the amount of CO2, and dividing that by the total mass, will get you the purity! They should specify that more explicitly in modern exams.

[:3]

It's talking about dry ice-that's solid carbon dioxide 

I'm so silly, of course it is.

Thank you.

[jakesilove]

For Q 18 of the 2010 paper, why is the answer C?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2010exams/pdf_doc/2010-hsc-exam-chemistry.pdf

For D : When the Ammonium and Chloride dissociate, wouldn't the positively charged ammonium ion ionise with the hydroxide in the water, creating water and ammonia?

And for HSC 2006 Q8, given that they have the same concentration, wouldn't that mean that they are equally dilute/concentrated?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2006exams/pdf_doc/chemistry_06.pdf

For question 18, all I can really say is that sodium acetate is a basic salt, and ammonium chloride is an acidic salt. We want to add a base, so that the equilibrium shifts to the left, and so we add sodium acetate! I was always bad with this sort of thing, so can't help out more than that.

For question 8, they don't actually have the same concentration? One is 0.1mol/L, the other is 1mol/L. Does that fix your issue?

[RuiAce]

For Q 18 of the 2010 paper, why is the answer C?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2010exams/pdf_doc/2010-hsc-exam-chemistry.pdf

For D : When the Ammonium and Chloride dissociate, wouldn't the positively charged ammonium ion ionise with the hydroxide in the water, creating water and ammonia?

And for HSC 2006 Q8, given that they have the same concentration, wouldn't that mean that they are equally dilute/concentrated?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2006exams/pdf_doc/chemistry_06.pdf

Is there a particular reason why you asked the same questions again?

For Q 18 of the 2010 paper, why is the answer C?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2010exams/pdf_doc/2010-hsc-exam-chemistry.pdf

For D : When the Ammonium and Chloride dissociate, wouldn't the positively charged ammonium ion ionise with the hydroxide in the water, creating water and ammonia?

And for HSC 2006 Q8, given that they have the same concentration, wouldn't that mean that they are equally dilute/concentrated?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2006exams/pdf_doc/chemistry_06.pdf

So I'll assume that you figured out why A and B are wrong (neutral salts).

Be careful as to which is the conjugate acid and which is the conjugate base here. H⁺ is the conjugate acid of H₂O

Yes, soon enough you'll have NH₃ and what not forming but what happens at the start? What you're adding isn't NH₃, it's NH₄Cl. That's the first thing that comes into contact with the mixture

When the ammonium chloride dissociates, the NH₄⁺ will rush to react with the H₂O already there. This causes the equilibrium to shift to the RIGHT (as per LCP), which is what we DON'T want here.


Instead, by adding sodium acetate, the CH₃COO^- will rush to react with the H⁺ instead. This forces the equilibrium to shift to the left to produce the chromate ions that we do want.

[:3]

Sorry...multiple choice questions.
Questions:
- 13: how do you know whether the curve continues up (B), instead of down (A) (thought equilbrium will move down).
- 15: what is the quickest way of doing these types of questions (all I can think of is doing them separately)?
- 17
http://www.boardofstudies.nsw.edu.au/hsc_exams/2014/pdf_doc/2014-hsc-chemistry.pdf

Thanks again, really appreciate that you're answering some of my questions (even though some are idiotic/simply there).

[jakesilove]

Sorry...multiple choice questions.
Questions:
- 13: how do you know whether the curve continues up (B), instead of down (A) (thought equilbrium will move down).
- 15: what is the quickest way of doing these types of questions (all I can think of is doing them separately)?
- 17
http://www.boardofstudies.nsw.edu.au/hsc_exams/2014/pdf_doc/2014-hsc-chemistry.pdf

Thanks again, really appreciate that you're answering some of my questions (even though some are idiotic/simply there).

For 13, I'm almost certain the answer is A, not B. Basically, I'm sure you're right, and the answer are wrong.

Unfortunately, there isn't a quick way for Q 15. You just need to do all of them, and see which is your answer?

For 17, you should be able to go straight to your table of standard potentials, find dichromate and and sulfer dioxide, invert the sign of the one highest on the list, and add up the two potentials!

[Cindy2k16]

Hi for this question Evaluate the impact on society of the environmental issues associated with 7 THREE of the industrial processes that you have studied in this option.  (industrial chem) is the extraction of sulfur counted as an industrial process on it's own or if we wanted to discuss it would we have to also talk about the production of sulfuric acid from sulfur?
TIA

[RuiAce]

For 13, I'm almost certain the answer is A, not B. Basically, I'm sure you're right, and the answer are wrong.

But if the volume is halved, then the pressure is increased right? Which favours the side with the fewer moles of gas?

I just glanced at it quickly, not too sure. Can only tune in for so long at a time

[jakesilove]

But if the volume is halved, then the pressure is increased right? Which favours the side with the fewer moles of gas?

I just glanced at it quickly, not too sure. Can only tune in for so long at a time

But after it's gone up, it should go back down a little to compensate for the change in concentration (ie. massive jump to favour the side with fewer moles of gas, then small decline to compensate)

[jazzaa36]

Yo does anyone have a simple way of remebering what effect water has on the concentration when left on apparatus of volumetric analysis ?

[jakesilove]

Hi for this question Evaluate the impact on society of the environmental issues associated with 7 THREE of the industrial processes that you have studied in this option.  (industrial chem) is the extraction of sulfur counted as an industrial process on it's own or if we wanted to discuss it would we have to also talk about the production of sulfuric acid from sulfur?
TIA

Hey! I didn't do this option, but it sounds totally fine to have an answer including that

[RuiAce]

But after it's gone up, it should go back down a little to compensate for the change in concentration (ie. massive jump to favour the side with fewer moles of gas, then small decline to compensate)

You lost me there. I was just using LCP on the equation given.

The change in concentration volume is the spike, and then LCP takes place after the spike.

[jakesilove]

Yo does anyone have a simple way of remebering what effect water has on the concentration when left on apparatus of volumetric analysis ?

Do you mean in terms of titration? You just sort of need to logic it out. If there is water left in the burrette, the base will be more diluted. That means you'll require MORE of it to neutralise the same amount of acid. So, you'll think that it is weaker than it actually is. Just think about it for a bit, there isn't really a quick way!

[RuiAce]

Hi for this question Evaluate the impact on society of the environmental issues associated with 7 THREE of the industrial processes that you have studied in this option.  (industrial chem) is the extraction of sulfur counted as an industrial process on it's own or if we wanted to discuss it would we have to also talk about the production of sulfuric acid from sulfur?
TIA

Oh I'll quickly address this one.

Technically, yes it IS involved with the production of sulfuric acid. We need to have a source of sulfur before we can start producing our sulfuric acid.

I'd say talking about it would be more beneficial here, because it's easy to link environmental concerns to the Frasch process

[Furrrball]

How do I calculate the percentage of total dissolved solids? Do I have to subtract the mass of suspended solids from the total volume of water?

http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2005exams/pdf_doc/chemistry_05.pdf

Q.25
2005 HSC