HSC Chemistry Question Thread

[Happy Physics Land]

is it a good idea to use other people s notes to study (but type own notes for questions like discuss, evaluate) because it takes too much time for me to make my own notes and it might not be as good as others

one ques about nuclear chem: will fusion always occur in reactor and fission occur in particle accelerator?

Hey Amanda:

Yep, nice question. Actually this question has been posted for quite a few times now on this forum, and Jake and I kinda have our own individual ways of responding to your concerns. Jake recommends to effectively use other people's notes from a variety of sources and choose and pick the best information for the particular syllabus dot point. For me, I usually type up my own notes. I would update my notes for every single subject (especially content based subjects such as chemistry and physics) every week. In this way I only have to spend 3 hours a week to basically make notes and revise through everything. As your notes accumulate you will be much better prepared for your exams. But of course this is only my approach and when Jake comes around he can give you more insights.

Regarding the nuclear chemistry question, I may like to inform you that this is definitely not always the case. In fact in nuclear reactors, fission would often be involved. I do understand where your perspective came from though, since our final desired radioisotope would only be produced through fusion with neutrons, which you have correctly stated. But if you consider how neutron bombardment is achieved, you can see the slight inaccuracy in your statement (sorry if lm being a bit too critical!)

Neutron bombardment which takes place in nuclear reactors actually begins with the FISSION of Uranium. When we add a neutron to Uranium-235, an extremely unstable state Uranium-236 is formed, which will only exist for 10^-12 seconds before splitting into fission fragments such as Barium-146 and Krypton-92. During this process, excess neutrons are also produced which then becomes the source for neutron bombardment. So as you can see, fission DO indeed take place inside nuclear reactors and fission of Uranium-236 is essential for fusion between neutron and other nuclei to produce the desired radioisotope.

In particle accelerators or cyclotrons you would have positive particles such as an alpha-particle or neutrons which are a result of spallation (fragmentation of other elements) being accelerated into a target nuclei to form a new radioisotope. Similar to what happens in nuclear reactors, we dont just get those neutrons or alpha particles from nowhere. We need another element to undergo fission to produce there particles that would allow us to form new isotopes. So your second statement about particle accelerators would be quite right, particle accelerators involve predominantly the nuclear process of fission.

So anyways I hope my explanation is clear to you and I really liked the question you asked because it is quite confusing since they are quite complicated to understand (those fancy gadgets these days). If you have any further concerns, please dont hesitate to ask!

Best Regards
Happy Physics Land

[jakesilove]

Hey Amanda:

Yep, nice question. Actually this question has been posted for quite a few times now on this forum, and Jake and I kinda have our own individual ways of responding to your concerns. Jake recommends to effectively use other people's notes from a variety of sources and choose and pick the best information for the particular syllabus dot point. For me, I usually type up my own notes. I would update my notes for every single subject (especially content based subjects such as chemistry and physics) every week. In this way I only have to spend 3 hours a week to basically make notes and revise through everything. As your notes accumulate you will be much better prepared for your exams. But of course this is only my approach and when Jake comes around he can give you more insights.

Regarding the nuclear chemistry question, I may like to inform you that this is definitely not always the case. In fact in nuclear reactors, fission would often be involved. I do understand where your perspective came from though, since our final desired radioisotope would only be produced through fusion with neutrons, which you have correctly stated. But if you consider how neutron bombardment is achieved, you can see the slight inaccuracy in your statement (sorry if lm being a bit too critical!)

Neutron bombardment which takes place in nuclear reactors actually begins with the FISSION of Uranium. When we add a neutron to Uranium-235, an extremely unstable state Uranium-236 is formed, which will only exist for 10^-12 seconds before splitting into fission fragments such as Barium-146 and Krypton-92. During this process, excess neutrons are also produced which then becomes the source for neutron bombardment. So as you can see, fission DO indeed take place inside nuclear reactors and fission of Uranium-236 is essential for fusion between neutron and other nuclei to produce the desired radioisotope.

In particle accelerators or cyclotrons you would have positive particles such as an alpha-particle or neutrons which are a result of spallation (fragmentation of other elements) being accelerated into a target nuclei to form a new radioisotope. Similar to what happens in nuclear reactors, we dont just get those neutrons or alpha particles from nowhere. We need another element to undergo fission to produce there particles that would allow us to form new isotopes. So your second statement about particle accelerators would be quite right, particle accelerators involve predominantly the nuclear process of fission.

So anyways I hope my explanation is clear to you and I really liked the question you asked because it is quite confusing since they are quite complicated to understand (those fancy gadgets these days). If you have any further concerns, please dont hesitate to ask!

Best Regards
Happy Physics Land

Love you HPL.

Just remember everyone that you don't really need to know all this stuff in as much depth as HPL has described above; but that shouldn't stop you from extending yourself! If there isn't an explicit dotpoint on the topic, you can't really be assessed on it. Look at past papers to figure out how much information you need to remember!

Jake

[curious.egg]

Helloo!

How would you use the equilibrium constant to describe the position of the equilibrium? Please help!!

Question:
" 2NO(g) ⇌ N2(g) + O2(g)               0.800 moles of NO was placed into a 2.00L vessel at 2000 degrees Celsius and the equilibrium concentration of N2 was found to be 0.198 mol/L. Calculate the equilibrium constant for this reaction and use this value to describe the position of the equilibrium. "

(industrial chemistry)

[amandali]

"given a geiger counter, outline a procedure by which you could determine the proportions of alpha and beta emissions from a sample of ac-277"  3 marks    im not sure what to write about    is it just describing the radiation entering the tube, ionising air molecules and generating audible clicks

[jakesilove]

Helloo!

How would you use the equilibrium constant to describe the position of the equilibrium? Please help!!

Question:
" 2NO(g) ⇌ N2(g) + O2(g)               0.800 moles of NO was placed into a 2.00L vessel at 2000 degrees Celsius and the equilibrium concentration of N2 was found to be 0.198 mol/L. Calculate the equilibrium constant for this reaction and use this value to describe the position of the equilibrium. "

(industrial chemistry)

Hey Mr. Egg!

I'll premise my answer with the fact that I didn't actually do Industrial chemistry, and despite having done Equilibrium constants at University would have no idea how to actually calculate that equilibrium constant.

However, your question isn't to calculate the constant but how we would then use this value to describe the position of the equilibrium. My university level Chemistry can definitely help with that part!

An equilibrium constant is used to describe whether there will be more of the products, more of the reactants, or an equal amount of both in a reaction.

The rule is as follows.

If

K > 1

then the equilibrium favors the products.

If

K < 1

then the equilibrium favors the reactants.

And that's it! So if you got an equilibrium constant of 1.1 in your calculations, you would just say that the position of the equilibrium lies slightly on the right (the side of the products). If you got an equilibrium constant of 0.1, you would say that the position of the equilibrium lies largely on the left (the side of the reactants).

Hope my explanation made sense!
If anyone that has actually DONE Industrial Chemistry would like to contribute, that would be supremely helpful!

Jake

[jakesilove]

"given a geiger counter, outline a procedure by which you could determine the proportions of alpha and beta emissions from a sample of ac-277"  3 marks    im not sure what to write about    is it just describing the radiation entering the tube, ionising air molecules and generating audible clicks

Hey Amandali!

This is a really tricky question, and to be honest one that I think falls largely outside the syllabus. Still, you could use your working knowledge of Geiger counters to come to some sort of answer!

I definitely agree that, first, you would explain how Geiger counters actually work (radiation entering the tube, ionising air molecules and generating audible clicks etc.). However, since it says "outline a procedure" and it is worth three marks, I would recommend actually pretending it was some sort of experiment. Knowing that ac-277 is radioactive, I would just spout something vague like "1. Place ac-277 in a location such that its radiation does not negatively effect human life. 2. Taking adequate precautions, direct a Geiger counter towards the ac-277. 3. As the (radiation entering the tube, ionising air molecules and generating audible clicks etc.), a certain value can be read and recorded from the scale placed on the Geiger counter."

Basically, just make sure that you identify that a specific amount of radiation can be detected (as per the scale on the counter) and that this is some sort of procedure, to make sure you get full marks!

It is really important that you read the question thoroughly and address each individual word. Hope this helps!

Jake

[FD121]

Any advice for Gravimatric Analysis SAC? It is a prac write up.

[jakesilove]

Any advice for Gravimatric Analysis SAC? It is a prac write up.

Hey FD121!

I think you're looking for the VCE Chemistry thread: This is the HSC Chemistry thread! As I don't know what is in your curriculum, I can't really answer your question.

Maybe repost your question here: VCE Chemistry Question Thread

Jake

[amandali]

The question is "Describe how commercial radioisotopes are produced, and how transuranic elements are produced" - 4 marks

Isn't this to much for a 4 marker ques ?


Commercial isotopes are used in medicine, industry and research. It can be produced in nuclear reactors where the target nuclei is bombarded with slow-moving neutrons which are then absorbed by the nucleus, thus forming a neutron-rich isotope.
eg.the medical isotope Cobalt-60 is produced in nuclear reactor (equation)

Neutron-deficient isotopes can be made in particle accelerators where the target nuclei collides with accelerated positively charged particles, causing fusion to occur.
eg.fluorine-18 is produced in particle accelerator
(equation)

Transuranic elements which have atomic masses greater than 92, can also be produced in nuclear reactor and particle accelerator, however, the target nuclei  is usually already large
eg. Neptunium-93 is made in reactor
(equation)

eg.Curium-242 is produced in particle accelerator (equation)

[jakesilove]

The question is "Describe how commercial radioisotopes are produced, and how transuranic elements are produced" - 4 marks

Isn't this to much for a 4 marker ques ?


Commercial isotopes are used in medicine, industry and research. It can be produced in nuclear reactors where the target nuclei is bombarded with slow-moving neutrons which are then absorbed by the nucleus, thus forming a neutron-rich isotope.
eg.the medical isotope Cobalt-60 is produced in nuclear reactor (equation)

Neutron-deficient isotopes can be made in particle accelerators where the target nuclei collides with accelerated positively charged particles, causing fusion to occur.
eg.fluorine-18 is produced in particle accelerator
(equation)

Transuranic elements which have atomic masses greater than 92, can also be produced in nuclear reactor and particle accelerator, however, the target nuclei  is usually already large
eg. Neptunium-93 is made in reactor
(equation)

eg.Curium-242 is produced in particle accelerator (equation)

Hey Amandali!

I definitely don't think that's too much for a four marker. I think it's always best to be SURE you get every single mark. By including loads of scientific jargon (which you did), and including great examples (which you did), you will absolutely get full marks. I think that is probably slightly longer than absolutely necessary, but in this case there really isn't much harm spending an extra 30 seconds to be sure you don't lose a mark.

Jake

[amandali]

hi  how do u do this question
"a small amount of pure sodium metal was dropped into 1.5 L of water. the collected gas occupied a volume of 18.6L at 25 degrees and 100 kpa. calculate concentration of hydroxide ions(aq) after reaction" ans:1mol/L

[RuiAce]

hi  how do u do this question
"a small amount of pure sodium metal was dropped into 1.5 L of water. the collected gas occupied a volume of 18.6L at 25 degrees and 100 kpa. calculate concentration of hydroxide ions(aq) after reaction" ans:1mol/L

The reaction between sodium and water is given as thus:

2 Na + 2 H2O -> 2 NaOH + H2

The gas collected is simply hydrogen gas. As we are at 25deg 100kPa, we have the molar volume Vm = 24.79
Hence, to determine the moles of H2:
n = V/Vm = 18.6/24.79 = 0.7503025413... mol

For each mole of H2 yielded, 2 moles of NaOH are yielded. Hence, moles of NaOH:
n = 2 * n(H2) = 1.500605083... mol

Note that one mole of {OH-} is present in one mole of NaOH, so the above answer gives us the moles of hydroxide ions present.

Hence, to determine the concentration, use C = n/V where V is the volume of water here
C = 1.500605083.../1.5 = 1.000403388 mol L^-1
= 1.0 mol L^-1 (correct to 2 sig. fig.)

[jakesilove]

The reaction between sodium and water is given as thus:

2 Na + 2 H2O -> 2 NaOH + H2

The gas collected is simply hydrogen gas. As we are at 25deg 100kPa, we have the molar volume Vm = 24.79
Hence, to determine the moles of H2:
n = V/Vm = 18.6/24.79 = 0.7503025413... mol

For each mole of H2 yielded, 2 moles of NaOH are yielded. Hence, moles of NaOH:
n = 2 * n(H2) = 1.500605083... mol

Note that one mole of {OH-} is present in one mole of NaOH, so the above answer gives us the moles of hydroxide ions present.

Hence, to determine the concentration, use C = n/V where V is the volume of water here
C = 1.500605083.../1.5 = 1.000403388 mol L^-1
= 1.0 mol L^-1 (correct to 2 sig. fig.)

RuiAce, looks like you'll be a big name on this community! Love your "Maths Challenge" forum, and this is a great answer, perfectly set out, that will really benefit everyone!

The only thing I would add, which I'm sure you would have done in an actual answer but didn't because of the formatting, is to make sure to always include states when writing out a chemical reaction. It's just an easy way to lose marks unnecessarily, so keep an eye out for that!

Again, thanks for posting the response! Keep at it!

Jake

[RuiAce]

RuiAce, looks like you'll be a big name on this community! Love your "Maths Challenge" forum, and this is a great answer, perfectly set out, that will really benefit everyone!

The only thing I would add, which I'm sure you would have done in an actual answer but didn't because of the formatting, is to make sure to always include states when writing out a chemical reaction. It's just an easy way to lose marks unnecessarily, so keep an eye out for that!

Again, thanks for posting the response! Keep at it!

Jake

Thank you! I'll stay around here more and do my best

As for the comment, yes I agree most definitely. I think if I were writing it out I would've just subconsciously written down the states.

[Maz]

Hi humans 
i did an experiment in class the other day- and i have a validation on it in the next couple of days...i was wandering if someone could please help me out? please
The experiment was on equilibrium and Le CHatelier's principle
first we got K2CrO7 and added HCl solution to it...then to the same solution we added the base NaOH. originally the K2CrO7 was yellow, with added HCl it went to a darker colour (around orange), then when we added NaOH to the solution it went back to yellow..
i did the first part of the experiment ok...but i need help with this bit
the question is: By referring to the collision theory, account for the observed colour change that occurred when NaOH solution and the HCl solution were added to the K2CrO7 solution
I'd appreciate any help