Chemistry - general thoughts on the exam (3 Viewers)

[StitchWitch27]

I thought the multiple choice was OK - except for the question on the phosphoric acid. That was insane. Thank God it's over! Part B was fairly decent, I think. I'm just glad they didn't ask a huge question on water quality because that would have finished me completely. I have no idea whatsoever about membrane filters. Gah.

What did people think about that question in part B with the pH of a solution of 50ml HCl 20mL NaOH (or something). Is it just me or would that be a neutral solution with pH 7 because they're both strong?

I really liked the option (shipwrecks) especially the 7-marker on restoration because my teacher had us do this HUGE assessment on restoration and so everyone in my class got to be basically experts.

 

[Triangulum]

What did people think about that question in part B with the pH of a solution of 50ml HCl 20mL NaOH (or something). Is it just me or would that be a neutral solution with pH 7 because they're both strong?

But there were different amounts with different concentrations. I think the way to do it was to work out how much of what substance would remain in excess once the neutralisation reaction completed, and then figure out what that made the pH.

 

[1qaz2wsxokm]

i got ph 7=P!

 

[lala2]

So the general consensus was that it was more tricky than actually being hard, and that there were a couple of 7 markers hanging in there for the options which most people liked? That's good to know, particularly the trick factor--a lot of people are on auto-pilot mode going in and don't read the question properly, so it'll really do quite a bit of separation. I felt my year's paper (2005) was quite ok.

 

[[Damo]]

You get pH 2 if you worked out the pH straight after figuring out the HCl that remained in excess, which was about 0.0098 mol. However, you needed concentration, and that value is just 0.0098 mol / 70mL. You had to convert that to mol/L, which came to about 0.14, I think. That gave you pH ~0.85.

I found it sort of OK - think I may have tripped up on a couple of the trick questions, and as expected I couldn't do acidic salts, sulphur compounds in the atmosphere or industrial reactions of ethylene very well. Hopefully I managed to bluff my way through them.

My option (Forensic) was great. Apart from the fact that I hadn't a clue what glycogen was or how enzymes affected polypeptides, it was almost perfect. The 7-mark was so broad you could essentially blather at length about any type of chromatography you liked. That was a good section.

My target for all subjects is high Band 5/low Band 6, so I'm hopeful. Can't be sure of anything, though.

pH= .85 is not correct, the pH is .9 (u had to round it up!)
this is because of the significant figure/decimal point rules associated with working out pH and [H3O] conc. the rule is; however many sig. figs they give concentration, is the amount of decimal places the pH must be. they gave conc to one sig fig, hence answer must be to one d.p. hence pH=.9

 

[toadstooltown]

Argh! I hate significant figures. Apart from the fact that my chem teacher doesn't completely understand them when there are zeros involved, I'm not a fan of any form of rounding and prefer to leave things exact (habit from maths). I'm sure I rounded incorrectly a few times but everytime I did I wrote (to __ sig.fig) next to it, noting the number in the qustion - hopefully they'll see I at least tried. They won't, but don't get the paper back so can live in blissful ignorance.

 

[4back89]

does ne 1 think that it was an alright test and you did alright but know that you don't wanna speak too soon.... i always seem to think i did pretty good in chemistry, like i answered all the questions right nd that but when ever i get em back its not that i got the question swrong its just theres is so much shit i left out in answering them... well i hope its not the case this time coz i studied a fair bit but i got a feelin it will hahaha...
and can ne1 tell me in the second last question of partB... it was the questiion with the flow diagram showing the different test for carbonates and chloride and that... Y were they in that order??? i left the question in the test to come back to but i ran outa time before i could. and how much was it worth?

 

[PF]

yeah i didnt know the one about why it had to be in that order - because Ca or Ba both give a white carbonate.... but it was onli a three marker ... overall a pretty decent test ... im pretty glad tho that they didnt ask abt solvay process - they skipped the whole thing!!!

 

[majan]

pH= .85 is not correct, the pH is .9 (u had to round it up!)
this is because of the significant figure/decimal point rules associated with working out pH and [H3O] conc. the rule is; however many sig. figs they give concentration, is the amount of decimal places the pH must be. they gave conc to one sig fig, hence answer must be to one d.p. hence pH=.9


u FOOOOL!!!!!.....its 0.85 cause u must give the answer to most significant figures that appears in the question.....and i am preety sure there was a figure in the question with 2 significant figures!

 

[Dropdeadbored]

Hey I found the Chem exam great, since my second last exam was Extension 1 Maths- yukky, awful.....

I found this quite an easy paper. Multiple choice questions were pretty good. The one about the catalysts of ethanol- I think I got that right. I tried to remember which catalyst was which by remembering that it wants to be ethanol... (don't ask, it just works for me) so I put a) as my answer.

And I just checked my notes and that is right

Question 4 was weird, because our class used Q=mcAt to work out enthalpy or something then divided by moles of ethanol used. I tried that and my answer was nothing like the last 2 choices, so I just put down b) which was the energy given out but not molar energy.

I absolutely loved the 7mark ethylene question. For those of you who found it hard, you talked about all the products you could make from ethylene- polyethylene, ethylene glycol (antifreeze), ethanol.... plenty of stuff there.

The acidic salt thing I couldn't remember either, but I also put ammonium chloride as my answer, because I wanted something that had Hs in it so they could make H3O+ in solution. So many people fluked that, I think it actually is acidic.

Shipwrecks was alright. So many questions could be fudged. The 7marks about restoration, I wrote about understanding REDOX etc. so we can use that to restore the metals etc. I even started talking about leaving things in water baths instead of letting them dry, to get rid of salts.... uh, duh......

Basically, if you had paid some attention to your studies, and wrote something, anything on the paper, you are bound to get some marks, even if they are marks of sympathy.....

Bye now and enjoy the next month of anxious waiting and partying...

 

[lala2]

Ya-ha, that's what you do at uni too if you're going under--rely on a lot of part marks for everything rather than full marks for high-mark questions. I think I will pass PHAR1616 only because of this way *shrugs*

 

[Carl_S]

I think you might have stuffed that Q entirely...not going to get 5/7...i think you should be hoping for any marks what so ever. NaOH doesn't replace a natural product.

I thought in general the test was quite easy.

Except i misread the 7 marker in industrial chem.

Instead of talking about a natural product that has been artificially produced, I talked about NaOH which isnt artificially produced... I'm hoping i can get up to a maximum of 5 for what i wrote based on a follow on error of using the wrong product... any thoughts??

 

[[Damo]]

pH= .85 is not correct, the pH is .9 (u had to round it up!)
this is because of the significant figure/decimal point rules associated with working out pH and [H3O] conc. the rule is; however many sig. figs they give concentration, is the amount of decimal places the pH must be. they gave conc to one sig fig, hence answer must be to one d.p. hence pH=.9


u FOOOOL!!!!!.....its 0.85 cause u must give the answer to most significant figures that appears in the question.....and i am preety sure there was a figure in the question with 2 significant figures!

sorry mate, in the question they only had to one sig. fig, the conc. was 0.02 and 0.01 if i remember correctly :S, i believe that is only 1 sig fig? and since conc. is to one sig fig, you must give pH to one dec. place. thats the rules of conversion of conc. to pH.