VCE Chemistry Free Trial Exam (2017) - written by me!

[gypsyakhyar]

Correction: Q5a) Solution doesn't include correct units (should be M^-1)

[VanillaRice]

Question: 2bi) How do we determine if amount refers to volume or mass?

'Amount' usually refers to the number of mole. Mass and volume are usually explicitly specified.

Question: Q3 Why are we only getting singlets in the proton NMR?
(sorry for spam, this is exam is awesome, just need help haha)

Recall low resolution proton NMR - where essentially splitting isn't present. Compare this to high resolution proton NMR, where signal splitting can be present.

Hope this helps

[gypsyakhyar]

'Amount' usually refers to the number of mole. Mass and volume are usually explicitly specified.
Recall low resolution proton NMR - where essentially splitting isn't present. Compare this to high resolution proton NMR, where signal splitting can be present.

Hope this helps

Thanks heaps man, great help!

[VanillaRice]

Thanks heaps man, great help!

I'd like to add something to my response RE: singlets on the proton NMR. From looking at the suggested answer, it turns out the question intended that there was no splitting present either way (whether it was high or low resolution). The reason for this is the hydrogen environments in the molecule have no adjacent hydrogen environments, so there is no splitting.

Hope that clears things up

@Phenomenol Do you think it would be a good idea to specify explicitly that it is a high resolution proton NMR spectrum?

[gypsyakhyar]

I'd like to add something to my response RE: singlets on the proton NMR. From looking at the suggested answer, it turns out the question intended that there was no splitting present either way (whether it was high or low resolution). The reason for this is the hydrogen environments in the molecule have no adjacent hydrogen environments, so there is no splitting.

Rightio, on further inspection it seems I'm an idiot! Hahaha, thanks heaps for your help

[Phenomenol]

Thanks man! You're a legend. Just in Section B: Q1a. Power output, watts aren't a term that's used in the chemistry study design. Might confuse some students, such as myself (needed to do a cheeky google, haha!).

This is very true. I will change the question to "average energy production rate (in MJ/s)".

correction: Q4ai) proper iupac name for aminoethane should be ethanamine

Absolutely! Fixed.

Correction: Q5a) Solution doesn't include correct units (should be M^-1)

Another good find (I was unaware the units for K_c was added to the study design!). Fixed.

@Phenomenol Do you think it would be a good idea to specify explicitly that it is a high resolution proton NMR spectrum?

Indeed it would! Fixed.

Rightio, on further inspection it seems I'm an idiot! Hahaha, thanks heaps for your help

Don't be hard on yourself! Haha

I think that's everything addressed in the v4 update.

Thanks to both gypsyakhyar and VanillaRice for pointing out the numerous errors. I very much appreciate it!

[exit]

For 10a, is the zn cu2+ not touching each other the only valid answer? Can I talk about how cell voltage isn't an indicator of concentration at all? (or am i wrong)

[Eric11267]

For MC Q10 can you explain why the carbon dioxide mole is double the mole of ethanoic acid? What's the chemical equation?

[VanillaRice]

For MC Q10 can you explain why the carbon dioxide mole is double the mole of ethanoic acid? What's the chemical equation?

We can write an equation for the combustion of ethanoic acid as per other organic fuels (such as methane) by balancing C, H and O
Note: CH₃COOH = C₂H₄O₂

\(\ce{C2H4O2 + 2O2 -> 2CO2 + 2H2O}\)

Hope this helps

[Phenomenol]

For 10a, is the zn cu2+ not touching each other the only valid answer? Can I talk about how cell voltage isn't an indicator of concentration at all? (or am i wrong)

Funny story - this was what I originally intended the desired response for the question to be, until a student of mine pointed out that the Zn/Cu2+ collisions do not occur at all.

You're right with the fact that concentration does not directly increase the cell voltage in the same way that it has a direct proportion with current. I would probably say that you would still get full marks if you pointed this out, because you ARE applying your knowledge of the chemical principles you have learnt this year

Having said that, I am not very familiar with how experimental design questions are marked so I am not 100% sure... but on a good day I would mark that sort of response as correct!

For MC Q10 can you explain why the carbon dioxide mole is double the mole of ethanoic acid? What's the chemical equation?

Following on from VanillaRice's explanation, a quick mental check of the fuel/CO₂ ratio is to note that all the carbon in the reactants is in the fuel, and all the carbon in the products is in CO₂. So you can determine the fuel/CO₂ ratio by balancing the carbons in each (circumventing balancing the entire equation!)

[manishmao]

Hey, for question 16 multi choice, the solutions state that pressure inside a solution calorimeter is varied, and volume inside a solution calorimeter is constant. The solutions also state that the opposite is true for a bomb calorimeter. However, online sources state the direct opposite of this i.e. A bomb calorimeter is referred to as a constant-volume calorimeter and a solution calorimeter is referred to a a constant pressure calorimeter. Why is this? Thanks a lot for the exam by the way.
Source: https://courses.lumenlearning.com/boundless-chemistry/chapter/calorimetry/

[Tknight]

i lost 21 marks whoops 13 on MC

[manishmao]

Also isn't higher concentration = greater cell voltage? I thought the E0 values were an indicator of how "out of equilibrium" (i.e. the reaction quotient), so wouldn't a higher concentration of one of the reactants push the system out of equilibrium further and hence drive up the cell voltage.

[thushan]

I had a look through the exam paper.

Excellent work. I was particularly impressed with your IR/NMR question; I would never have thought of a question that had that perfect balance between challenging and doable.

I'll promote this on VCE DiscussionSpace because it is definitely an excellently written paper.

[Phenomenol]

Hey, for question 16 multi choice, the solutions state that pressure inside a solution calorimeter is varied, and volume inside a solution calorimeter is constant. The solutions also state that the opposite is true for a bomb calorimeter. However, online sources state the direct opposite of this i.e. A bomb calorimeter is referred to as a constant-volume calorimeter and a solution calorimeter is referred to a a constant pressure calorimeter. Why is this? Thanks a lot for the exam by the way.
Source: https://courses.lumenlearning.com/boundless-chemistry/chapter/calorimetry/

You're absolutely right :/
This is a complete oversight by me. I will also probably need to alter this question to be slightly more applicable to the study design. Will fix ASAP.

i lost 21 marks whoops 13 on MC

You did really well! The MC is definitely on the very tough side of things.

Also isn't higher concentration = greater cell voltage? I thought the E0 values were an indicator of how "out of equilibrium" (i.e. the reaction quotient), so wouldn't a higher concentration of one of the reactants push the system out of equilibrium further and hence drive up the cell voltage.

You are right. The cell voltage under non-standard conditons can be calculated from the Nernst equation. It is true that decreasing concentration of product ions/increasing concentration of reactant ions will both lead to increase in cell voltage, however it is worth noting that both relationships are logarithmic.

If the student had provided your reasoning in his hypothesis it would be very sound

I had a look through the exam paper.

Excellent work. I was particularly impressed with your IR/NMR question; I would never have thought of a question that had that perfect balance between challenging and doable.

I'll promote this on VCE DiscussionSpace because it is definitely an excellently written paper.

Thanks so much. This paper is still being improved as peer review continues but it is nearly what I envisioned it to be.