HSC Chemistry Question Thread

[noonedoesnt]

We know that



After realising it's a 1:1 reaction, and noting that the moles of each substance must be the same. Therefore




Therefore, in 100mL, there would be



If 1 gram is that many moles, then




Is that the answer? I'm seriously tired and I may have made a calculation error, but that's the method

yeah thats the answer, thanks heaps

[jakesilove]

yeah thats the answer, thanks heaps

No problem! Aha I'm super glad I got that right.

[massive]

guyyys how do you do the q attached, the answer is c

[wesadora]

Oh ok thank you!

Also some other questions..
1. Is there a simple equation for a radioisotope produced in a cyclotron? The one I have (Iodine 123) is quite complicated so it's hard to memorise and I was wondering if there were any more basic ones?

2. Do we need to know how our chosen radioisotopes (medical, industrial) are produced?

TIA

if you're just referring to a 'radioisotope' and not a transuranic (i have one for this - californium, but its not as simple), I just use one for Fluorine-18.

Bombardment of nitrogen-14 (which is just how it exists normally, check periodic table) with a normal helium nuclei, to make Fluorine-18. Adds up nicely and pretty simple, just adding standard nitrogen and helium!
Note - fluorine-18 is a neutron deficient radioisotope, which you'll find is what happens when you do this kind of light nuclei bombardment in cyclotrons (as opposed to neutron bombardment, which creates neutron rich radioisotopes) because the neutron to proton ratio for a stable atom increases the higher you go up the periodic table (e.g. helium is 1:1, while platinnum is exactly 1.5)

[wesadora]

guyyys how do you do the q attached, the answer is c

all you're doing, is dividing the molar mass of propylene (given) by the molar mass of propene - in order to find out how many propenes there are in the entire propylene chain (molecule). You know there are 3 carbons per propene, and so times the number of propenes by 3, to find the total number of carbons. lel

[jamtimsal]

Petroleum and sugar cane are both raw materials used for the production of ethanol. Construct separate flow diagrams for the production of ethanol from each raw material. (5 marks)

Petroleum Sugar Cane
(Required to draw separate flow charts -->)

Pretty sure this was a past HSC question but can't find it at the moment.

Just wondering what level of detail is required for the 5 marks. I remember the sample answer being almost unnecessarily specific (like ratio's of chemicals and fully explaining the fermentation process)

[Cindy2k16]

Hi for industrial chemistry are we required to be able to write the chemical formula of a fat/oil? Or can we write the process of saponification with a general equation?
eg soap is RCOO^-Na⁺

Also when describing experiments is it necessary to have quantities eg. 10mL of water or is describing qualitatively sufficient?
TIA

[RuiAce]

Hi for industrial chemistry are we required to be able to write the chemical formula of a fat/oil? Or can we write the process of saponification with a general equation?
eg soap is RCOO^-Na⁺

Also when describing experiments is it necessary to have quantities eg. 10mL of water or is describing qualitatively sufficient?
TIA

Umm I think RCOO^- Na⁺ will suffice. I haven't ever come across a question that needed me to specifically write out a correct chemical formula for one of them.

Though I did learn the "general" structure of it so that I could draw them. I found describing the structure of soaps and etc. hard so I drew a diagram to aid my description.


Unfortunately you will have to make a judgment on that one as for things such as esterification you should be writing quantitatively. Think about where quantities actually won't matter (potentially, experiments without calculations), then you can write something qualitative (e.g. 3 drops)

[jakesilove]

Pretty sure this was a past HSC question but can't find it at the moment.

Just wondering what level of detail is required for the 5 marks. I remember the sample answer being almost unnecessarily specific (like ratio's of chemicals and fully explaining the fermentation process)

For a 5-8 markers, I would definitely be unnecessarily specific to ensure you get full marks. It takes four minutes to go through the whole fermentation process, and that's worth getting an extra mark for! Go through each step methodically, with every piece of information relevant in answering the question.

[noonedoesnt]

picked B, answer was A

[RuiAce]

picked B, answer was A

Careful, B is more suitable for the anode, not the cathode.

Because Pt is your cathode, you probably want something that involves a gas/aqueous half-cell.

[JemexR]

Could someone please do the working for HSC 2004 Q13 please? I have a ridiculously tiny number at the moment (not enough change in temperature). Thanks

[noonedoesnt]

Do we need to know the structure of amino acids as a condensation polymer?

[RuiAce]

Could someone please do the working for HSC 2004 Q13 please? I have a ridiculously tiny number at the moment (not enough change in temperature). Thanks

Please provide the question or a link to the paper in the future

Do we need to know the structure of amino acids as a condensation polymer?

Amino acids aren't in the HSC chemistry course...

Edit: Those notes ring a bell. Nothing wrong with it but I feel there's an overloaded amount of stuff there to memorise

[wesadora]

why is it that the strength of an acid/base does not affect the volume required for titration (rather, the concentration of the acids affects the volumes)? E.g. if both acid/base solutions are 0.1M it does not matter whether one or the other is weak or strong - the same volumes for neutralisation will be required.

This makes sense calculation wise for tritrations to me (n=cv), but, I thought that for neutralisation, it's based on H⁺ + OH^- --> H₂O, and the concentration of H+ in weak acids is less than the concentration of the acid, wouldn't this affect the volume neeeded for neutralisation?

but it doesn't. ._.