ATARNotes Official Solutions to VCAA 2012 Unit 4 Chemistry Examination

[thushan]

I think in chem you always get consequential marks if there was no other way of solving the question except by using the wrong answer you got in the previous question.

Otherwise you would have almost ended up like me in the Olympiad exam last year, where I got the first part of a 30 mark question wrong, and the Turkish examiners gave me like 18/30 because they docked a mark off each subsequent part. My Australian mentors had to argue with them for like 2 hours to convince them to give me the consequentials - ended up getting 29/30 for that qn. LOL.

[Tombraider28]

Hey Thushan, with question 3c. because the HCl is aqueous, I mentioned that the water would react with the sorbate ion, driving the reaction forward increasing [Sorbic Acid], and also would'nt the h+ ions from HCl and OH- ions react to form more water which would then react more with sorbate ion, or am I just going a bit overboard and sound like a dumbass . I just thought that if H2o is present it would react with the sorbate ion and form sorbic acid as the equation depicts. And like you said a forward reaction occurs due to the decrease in OH- ions from the HCl, and then I would have thought that the OH-ions react with the H+ ions to form more water and hence the water present causes the forward reaction to be favoured to then act to reduce the increase in water. I am a bit overboard aren't I. Will I get a mark for saying Sorbic acid concentration has increased. Don't judge me.

[thushan]

Dude, why would I judge you?

:/ you over thought the question. You are right in saying that the HCl is aqueous, and yes, we have added extra water because HCl is aqueous, however the concentration of water doesn't change (water is a liquid) - so you can't really say that the forward reaction rate increases because of addition of water.

You were absolutely right in your point about H+ reacting with OH- to form water, but the extra water in itself doesn't cause an increase in the forward reaction rate, because the concentration of water never changes.

But you'd get 1/2 for that.

[Tombraider28]

@Thushan. Oh okay, I am happy with one mark at least, so water does not do anything, alright understood, also I just wanted to ask about uni chem, is it better than in vce, cause i hated vce absolutely hated it, did not enjoy year 12 at all  . I love chemistry alot and would love to continue it throughout my future it is one of my passions. I just wish I could have been better at it this year, but I suppose I can't complain because I tried my best. I got an A for mid year and I hope for an A+ end of year, what could I get as a study score with possibly A+ sacs. I feel if I say something wrong I sound stupid. What I find confusing and frustrating, is that I was essentially learning new content from the practice exams that I attempted, rather then the textbook which had jack crap, only about basic concepts. I read the textbook like three times and annotated the absolute crap out of it, and all the information (relative to exam style questions) that I picked up from these practice exams was completely new and was not contained within the textbook.  Is it like that in Uni, I would like to know to get mentally prepared, because I have picked on that concept and found that it has helped. I also used a bit of general knowledge from chemistry to help me with exam questions. I love learning new things in chemistry, I just wish it was all together for you, so you you don't have to do every exam possible ever made to try an understand exam style questions. Sorry for the long message, I like talking about chemistry and what not.   

[thushan]

"I feel if I say something wrong I sound stupid."

Yeah, I know the feeling; however, remember that it's all a learning experience, and we're not going to judge you for saying something wrong. Hell, I've said many wrong things, on AN too.

Which textbook do you have?

Hmm, from my experience at uni, for uni chem the course is generally well-structured - the lectures are good, the textbook a good supplementary resource. However, in other courses such as med, the amount that you have to know in the exam is not specified - so you often get the most random of questions, so to get 100% you basically have to know everything there is to know.

[Tombraider28]

I have the Heinemann Chemistry 2 Enhanced (I think that's how you spell it) it does not go into enough detail for my liking. And also, if you don't mind me asking, what sort of stuff do you learn in first year, is it similar? What course are you doing? I plan on doing a bachelor of science at monash, that is if I can get the Atar requirement. I have heard they are really good in the science area. 

[thushan]

Oh, I'm doing Med - did Monash Uni Chem during year 12.

[Tombraider28]

Oh do you still got to Monash, How do you find it? Also what do you think I could get as a study score, with A mid year, hopefully A+ sacs and I hoped to god A+ End of year? I just want to get a rough idea of where abouts I could be.

[thushan]

Yeah I still go monash

Um between I'd say 37-43.

[Nobby]

For SA. 6)c)ii) would you pay an answer explaining how a catalyst increases reaction rate, then saying that this allows the cell to draw more current?

[thushan]

Yeah, I'd pay that.

[Tombraider28]

Might see you there maybe in the future. 

[Tombraider28]

For that question you just answered, 6c.ii could you say that the catalyst increases the rate of that reaction occuring, and so without the catalyst, the rate of the reaction occuring would be very slow. I just talked about rates of reactions, because I thought they were asking specifically about why the catalyst is important for the reaction in decreasing activation energy.  I did not know you to say that current was increased. It is only worth one mark, isn't it? Oh man

[doc2]

Some slight suggestions

6b The calibration factor allows for the insulation of the calorimeter, so I dont think the first answer would be OK
Other possibilities include
Incomplete combustion- ie production of CO not CO2
Weighing error or loss of Methanol on transfer to calorimeter

8b  The key thing is that a lot of energy goes into drying the coal (mention latent heat if you wish)
9(a) The state of Br2 should be (g) at these temperatures.

[charmanderp]

8b  The key thing is that a lot of energy goes into drying the coal (mention latent heat if you wish)

Would this change the amount of energy that is produced though via combustion though?