VCE Chemistry Exam Discussion and Solutions (in progress)

[Willba99]

I think that question 2 in MC should be B - its the lowest temp range above freezing point. I think, as its an lithium ion battery, they're implying the presence of water, so it has to be above freezing point to function, but other then that I think the lowest possible temp will decrease the rate of unwanted reaction in the battery. Thats just my two cents, I'm reasonably certain my teacher said we didn't have to know about specific batteries anymore...

EDIT: here's a page I found. Not sure about its validity, but it seems to support what I'm saying:
https://arstechnica.com/gadgets/2011/02/ask-ars-what-is-the-best-way-to-use-an-li-ion-battery/

[bentennason]

Hi guys,

I have checked the both the mc answer short answer questions, but I need a bit more of checking with my answers to short answer questions.

For question 1, I did write H2O and MnO4/H+, but do we absolutely have to write states - I didn't for these? Like for the reaction between propanol and ethanoic acid, I wrote all of the reactants and products in liquid state? And also, do we have to absolutely include the H2SO4 catalyst for the formation of ester? (I forgot this)

For question 6ai, would it be okay for one mark to say that the electrolyte helps to carry ions between the electrodes so that they could react to form the products required?

For question 6bi, when it says 'state two advantages of PEM fuel cell', I mentioned that the fuel cell is more energy efficient compared to diesel engine, and also that it is more environmental friendly as no CO2 is produced. Would this be okay? (by the way, there is such thing as a closed system diesel engine in submarines)

For question 8d, when it says that why carbon anode cannot be interchanged with iron, I did say that iron is a stronger reducing agent and oxidises in preference to fl-, however, my half equation had the wrong state for Fe2+ cos I said that it was 'aq' instead of 'hf'. Would I get penalised for this?

For question 9b, would concentration of NaOH be an appropriate controlled variable - cause I said that higher concentrations of NaOH will result in less titre being delivered?

For question 9f, I wrote for preparing the solution you needed 'safety glasses, gloves and gas mask' and for conducting titration you needed 'safety glasses, gloves'. Would this be correct?

6ai) seems ok albeit not mentioning "hydrogen ions" as in this case you do know ion's identity

6bi) not sure if there is a context behind the question, ie. you don't want to be detected while underwater, don't want to pollute the local environment with CO2...
if there is context, i reckon both your CO2 argument and efficiency are valid; the unreacted gas looks like it can be pooled again.

9b) a good point. although if you literally use a more concentrated solution of NaOH (ie. using 0.55M vs 0.50M), the result will not change. your argument only applies if you're thinking you're using 0.50M, but in actual fact it is 0.55M. depends on wording

9f) what about a lab coat? we doin this in boxers, flip flops and a singlet? edit: luckily i didn't sit this exam

[Deonyi]

It said excepting a lab coat.

[thushan]

Question 10 is D. Zwitterions by definition are uncharged overall.

Also, question 15 is B. Alcohol does disrupt hydrogen bonding.

[thushan]

I think that question 2 in MC should be B - its the lowest temp range above freezing point. I think, as its an lithium ion battery, they're implying the presence of water, so it has to be above freezing point to function, but other then that I think the lowest possible temp will decrease the rate of unwanted reaction in the battery. Thats just my two cents, I'm reasonably certain my teacher said we didn't have to know about specific batteries anymore...

EDIT: here's a page I found. Not sure about its validity, but it seems to support what I'm saying:
https://arstechnica.com/gadgets/2011/02/ask-ars-what-is-the-best-way-to-use-an-li-ion-battery/

Lithium ion batteries don't contain water; if they did, the battery would explode since Li and H2O react violently to form H2.

[MG226]

Does anyone have any sample solutions for short answer? I know some are quite open so obviously are not a proper guide as to what VCAA will mark as correct but just want an idea of what should have been said

[keltingmeith]

Does anyone have any sample solutions for short answer? I know some are quite open so obviously are not a proper guide as to what VCAA will mark as correct but just want an idea of what should have been said

Working on it, sorry. Had important meetings today I had to deal with, then had to help my mum with her computer (who is so bad with them she had to make a shortcut to her desktop).

[MG226]

Working on it, sorry. Had important meetings today I had to deal with, then had to help my mum with her computer (who is so bad with them she had to make a shortcut to her desktop).

No need to apologise! Not something anyone is obliged to in anyway. Sorry if that was a bit impatient or demanding sounding, I just have a tendency to overthink things and convince myself that I fail everything lol... and then I wonder why I don’t sleep. Seriously though, no rush - you guys don’t HAVE to do this all for us and have other things that need to be done before writing up solutions for anxious year 12s. I can imagine these would be a bit time consuming too as there are various answers for some questions, especially the last 2. Thank you for taking the time to do them

[lovebiology]

But could Q23 of MC be indicating that by sampling from different sources, accuracy could be improved? Which means that the sampling bias is minimized so that the experimental value is closer to the true value? Can someone help me out?

[keltingmeith]

But could Q23 of MC be indicating that by sampling from different sources, accuracy could be improved? Which means that the sampling bias is minimized so that the experimental value is closer to the true value? Can someone help me out?

But it wouldn't improve accuracy, it would improve precision. If there is a sampling bias, as each sample is collected in the same way, the bias would exist in each, still.

It is inherently a good idea to collect from multiple samples - but to increase precision. You can't improve accuracy except by taking extra care with sample prep, and that's why C isn't the right answer - not because taking multiple samples is a bad idea, but because it won't improve accuracy, which is what the answer says it does.

[lovebiology]

Thanks for the reply! But I thought increasing the sample size improve precision, whereas limiting sampling bias improve accuracy... Or am I so wrong...

[keltingmeith]

Thanks for the reply! But I thought increasing the sample size improve precision, whereas limiting sampling bias improve accuracy... Or am I so wrong...

Limiting sampling bias does improve accuracy, but sampling from multiple places isn't going to decrease sampling bias, it's going to increase the sample size.

[dan0038]

can someone plz post the solutions. been waiting for agess 

[keltingmeith]

can someone plz post the solutions. been waiting for agess 

There's some solutions to the MCQ in the first post (a couple of them need to change), I'll be working on the short-answer questions tonight.

[Bri MT]

can someone plz post the solutions. been waiting for agess 

Please remember that the kind people who use their time to write solutions are volunteers