VCE Chemistry 3/4 Examination 2015 - Discussion Thread

[odeaa]

Nearly did it wrong myself too because I didn't notice it said to find the n(HCl) reacted in the titration flask (20mL aliquot). So the initial amount of HCl had to be multiplied by 20/250, then you could subtract the amount of n(Hal) reacted. In the end the concentration I calculated was a little lower than the one that was in the information.
Hopefully I got that right...

yeah i got like 43 or something just under, i was certain i'd fucked up but that reassured me

[bobisnotmyname]

for the last back tittation question explaining the error. would i get a mark for say water could have evaporated from the solution (my answer I had like 94g/L) ?

[Bruzzix]

Here is the exam:
http://bit.ly/1MIaqcr
I will be posting this link in the exam copy thread as well.
Edit: someone beat me to it

[Splash-Tackle-Flail]

Nearly did it wrong myself too because I didn't notice it said to find the n(HCl) reacted in the titration flask (20mL aliquot). So the initial amount of HCl had to be multiplied by 20/250, then you could subtract the amount of n(Hal) reacted. In the end the concentration I calculated was a little lower than the one that was in the information.
Hopefully I got that right...

Oh crap I think I multiplied the concentration of excess by 250/20, cause molar ratios? This is the same as multiplying the initial by 20/250 right?

[Bruzzix]

Oh crap I think I multiplied the concentration of excess by 250/20, cause molar ratios? This is the same as multiplying the initial by 20/250 right?

That's what I did too.. I don't even want to think about the exam anymore haha :p

[Stick]

Looks like many of the things I specifically mentioned to my students came up on the exam, so I'm obviously rather happy about that.

[zsteve]

I ended up writing some of the worded responses on the adjacent page (with appropriate linking arrows) and also on the bottom margin, as I made mistakes initially. Just checking that the examiner would be able to read those? (pls pls pls ) I assumed the entire paper was fair game for writing on except the black strip

Btw the exam was easier than expected - I was bracing myself for 2014

[Splash-Tackle-Flail]

I ended up writing some of the worded responses on the adjacent page (with appropriate linking arrows) and also on the bottom margin, as I made mistakes initially. Just checking that the examiner would be able to read those? (pls pls pls ) I assumed the entire paper was fair game for writing on except the black strip

Btw the exam was easier than expected - I was bracing myself for 2014

As long as you indicated (which you did), they will read it- you'll be OK

[zsteve]

Was pH = 4.5 for the H2S question?

[Bruzzix]

Was pH = 4.5 for the H2S question?

I'm pretty sure it is, that was my answer too

[zsteve]

I'm pretty sure it is, that was my answer too

Hmm... what did you write for disadvantages of the hydrogen fuel cell for cars? I wrote that H2 was not readily available and widely distributed as petrol... lol not chemistry but I guess this was where it was heading

[Bruzzix]

Hmm... what did you write for disadvantages of the hydrogen fuel cell for cars? I wrote that H2 was not readily available and widely distributed as petrol... lol not chemistry but I guess this was where it was heading

For advantage I said it is more efficient than a combustion engine because there are few energy conversions and for disadvantage I said more expensive to operate.

[zsteve]

For advantage I said it is more efficient than a combustion engine because there are few energy conversions and for disadvantage I said more expensive to operate.

Hmmm... do you think my response would be accepted then :/ I saw it on the Heinemann textbook so I thought ... yes

[bobisnotmyname]

For disadvantage I wrote hydrogen gas is highly reactive and dangerous in an accident, would this get a mark?

[thushan]

I'm pretty sure it is, that was my answer too

Yeah, I got 4.5