VCE Chemistry Question Thread

[Swagadaktal]

thanks

For example
Say in this electrolytic cell there is no membrane seperating the reduction and oxidation
At the Anode we have : \(\ce{2H2O(l)->O2(g) + 4H+(aq) +4e-}\)
At the Cathode we have : \(\ce{2H2O(l) + 2e- -> H2(g) + 2OH-(aq)}\)
Overall is : \(\ce{2H2O(l) -> O2(g) + 2H2(g)}\)
How do we test that the reaction has occured. Can we use universal indicator since H+ is produced at the anode changing pH and like wise with OH-  at the cathode but i'm thinking OH- and H+ react to produce H2O thus no change in pH.
Will they react fast enough for us to be unable to do the test?
Would the only way to check is to observe O2(g) and H2(g) bubbles formed?

If you add a universal indicator to the solutions around both the cathode and anode, you should notice that they change colours. Whilst the overall pH stays the same, around both electrodes there should be a higher concentration of either H+ or OH- ions depending on which electrode it is. There you should be able to observe some kind of colour change due to change in pH

[blacksanta62]

Hey guys, is it a smart idea to think of heat of combustion as the change in enthalpy (like normal reactions) but for combustion? Like, is that all it is? Or is it more special than that. Hope this made sense

[Sine]

Hey guys, is it a smart idea to think of heat of combustion as the change in enthalpy (like normal reactions) but for combustion? Like, is that all it is? Or is it more special than that. Hope this made sense

Yes its just delta H with a subscript c, remember it's per mole as per the data book.

[blacksanta62]

Yes its just delta H with a subscript c, remember it's per mole as per the data book.

So I can work it out in the same way as normal delta H?
Thank you

[mytime]

hey, just out of curiosity, if I'm averaging 62% on SACs, in a strong cohort (macrob) around what score do i need in the exam to get a minimum 38 raw SS? thanks for your help

[sweetcheeks]

I am wondering how many marks you can drop on the exam and still get a 50?

[Sine]

I am wondering how many marks you can drop on the exam and still get a 50?

2013 - 6 marks
2014 - 4-5 marks (not 100% sure on this one)
2015 - 2-3 marks

[Elizawei]

Hey guys quick question, how would you recommend using reading time for chem exam?
E.g. allocate 5 min for MCQ and 10 to rest? etc.
Would love to hear your suggestions

I would spend 2-5 minutes skimming over the entire paper first, to note down the areas that require more thinking (or to internally high 5 yourself because you feel confident ). Then devote rest of your time to multiple choice. I like to do my exam chronologically in the order that they appear so I guess this way of divvying reading time up works for me

[Jakeybaby]

Hey guys quick question, how would you recommend using reading time for chem exam?
E.g. allocate 5 min for MCQ and 10 to rest? etc.
Would love to hear your suggestions

As soon as the reading time starts, I would immediately write down any important conversion tables (concentration conversions), and equations of which you tend to forget or make simple errors in. If you do this at the beginning, spending 2-3 minutes doing it, it'll be fresh in your mind and then you can concentrate on reading through questions.
Here in SA, we don't have multiple choice in Chem nor Physics, but if you do, I would suggest going through most of these first, as that is what works best for me.
If you feel confident with the multiple choice, I would immediately start looking through for questions which you seem iffy about. A good technique which I was told by my math teacher (although, it didn't personally work for me) is to write down each question number, and then place a:

• Tick - if you're confident with the question, easy marks
• Question Mark - If you're 50/50 on the approach/knowledge needed in the question, you've sort of got an idea, but not 100% sure

[li]Cross - No idea on where to start nor approach the question from, hopefully you'll remember as the exam progresses.
[/li][/list]
If you have placed a tick next to Qu. 3, 4, 6, 8, 12, 15 - do these first, get the marks that you know that you can get first!
Then move onto the question marks, and then the crosses.

I'm also not 100% sure on the structure of your exam, but here in SA, we have some extended response questions (usually worth 16 marks), finding these questions in the exam and immediately writing down key ideas surrounding it is essential.

[Sine]

As soon as the reading time starts, I would immediately write down any important conversion tables (concentration conversions), and equations of which you tend to forget or make simple errors in. If you do this at the beginning, spending 2-3 minutes doing it, it'll be fresh in your mind and then you can concentrate on reading through questions.
Here in SA, we don't have multiple choice in Chem nor Physics, but if you do, I would suggest going through most of these first, as that is what works best for me.
If you feel confident with the multiple choice, I would immediately start looking through for questions which you seem iffy about. A good technique which I was told by my math teacher (although, it didn't personally work for me) is to write down each question number, and then place a:

• Tick - if you're confident with the question, easy marks
• Question Mark - If you're 50/50 on the approach/knowledge needed in the question, you've sort of got an idea, but not 100% sure

[li]Cross - No idea on where to start nor approach the question from, hopefully you'll remember as the exam progresses.
[/li][/list]
If you have placed a tick next to Qu. 3, 4, 6, 8, 12, 15 - do these first, get the marks that you know that you can get first!
Then move onto the question marks, and then the crosses.

I'm also not 100% sure on the structure of your exam, but here in SA, we have some extended response questions (usually worth 16 marks), finding these questions in the exam and immediately writing down key ideas surrounding it is essential.

not too sure about South Aus

but you shouldn't be writing down anything during reading time - that is what writing time is for 
personally i feel if you know the stuff well enough there is no reason to have to write down all the formulae before you start answering questions.

[Jakeybaby]

not too sure about South Aus

but you shouldn't be writing down anything during reading time - that is what writing time is for 
personally i feel if you know the stuff well enough there is no reason to have to write down all the formulae before you start answering questions.

You may have it memorised, but you never know what you will forget under pressure, writing down key information will decrease the likelihood of this. During reading time, you should be writing notes on questions, rather than just reading through them. Then, when you get to the question in the exam, you won't have to decipher it all over again, as the bits that you read in reading time will now be completely useless, not writing during reading time is seen as waste of time in my opinion.[/list]

[NerdyPi]

Hi guy, I'm really stressing out about my chem SAC on Monday, and I was wondering if someone could please check my working.

This particular experiment was to determine ΔH of dissolution of KNO3 using calorimetry. In my prac, for calibration aspect, I got ΔT = 174.5 degrees Celsius, for a 21.391g aluminium block (and my teacher said we get told c for aluminium on SAC, for my prep I looked it up and got 0.9J/Cg) .

So I found energy with E = mcΔT = 21.391*0.9*174.5 = 3359J. I then divided this by the ΔT of 174.5 to get 19.25J/degrees c as a calibration factor.

I then times this my 1.5 degrees c, the ΔT when KNO3 was dissolved in water, giving 28.88J released in 2.998g KNO3. I then found the mol of the KNO3 (0.0297), and divided the 28.88 by it to get a value of 973.9J/mol for dissolution of KNO3 (and left it as this because the equation mol ratio was all 1to1).

These seemed like the logical steps to me (and obviously I'll be careful to use exact value on calc and round to correct sig figures in SAC), so was this working correct? Thanks a heap

[zsteve]

Hi guy, I'm really stressing out about my chem SAC on Monday, and I was wondering if someone could please check my working.

This particular experiment was to determine ΔH of dissolution of KNO3 using calorimetry. In my prac, for calibration aspect, I got ΔT = 174.5 degrees Celsius, for a 21.391g aluminium block (and my teacher said we get told c for aluminium on SAC, for my prep I looked it up and got 0.9J/Cg) .

So I found energy with E = mcΔT = 21.391*0.9*174.5 = 3359J. I then divided this by the ΔT of 174.5 to get 19.25J/degrees c as a calibration factor.

I then times this my 1.5 degrees c, the ΔT when KNO3 was dissolved in water, giving 28.88J released in 2.998g KNO3. I then found the mol of the KNO3 (0.0297), and divided the 28.88 by it to get a value of 973.9J/mol for dissolution of KNO3 (and left it as this because the equation mol ratio was all 1to1).

These seemed like the logical steps to me (and obviously I'll be careful to use exact value on calc and round to correct sig figures in SAC), so was this working correct? Thanks a heap

Your working looks fine to me (haven't checked numerical details, but the flow of steps is correct). Also make sure your final value for Delta H is negative, reflecting the fact that it's exothermic

[larissaaa_]

Question: predict the products of electrolysis of 1 M nickel sulfate solution sing copper electrodes.
Suggested answer begins with: The chemicals present at the electrodes are Ni²⁺ SO₄^2- and H₂O ...

How do we know those are what is present at the electrodes? Where did the sulfate go and why does water act as both an oxidant and reductant? Thank yoU!

[Rumena]

Hi guys,
I'm really struggling with the concentration conversions, could someone be really kind and summarise the conversions for me please?!😁