Howd you go on the chem exam?

[ghadz7]

Yep, that's what i got as well.

[stonecold]

pH to 3 decimal places?

[8039]

what was the correct E naught value ?
AgCl.... = +0.22V ?

I was confused... in experiment 3 hydrogen acts as a reductant... but has a 0.00V so wtf

[bubsy]

for question 19 i said A beacuse the reactants ARE stored within the fuel cell regardless of whether it is pumped continuously. all the other possible answers were plain wrong...so yeah.
hope i'm right.
i said biochemical was more sustainable cos its renewable?

they aren't stored. they are PUMPED IN - hence they were never originally stored in the cell. but i repeat, ALL ANSWERS WERE WRONG FOR Q19

THis is what i think.
Technically electrons do pass from the reductant to the anode though? Anode is just negative electrode?

Reductant (site of oxidation) is the anode. How the hell do electrons go from anode to anode.

This was my reasoning: Although the direction of electron through the wire is from anode to cathode, the anode is the site of oxidation, the loss of electrons from the reductant. These electrons are taken up by the anode (bad terminology ) and are then conducted to the cathode. All of the others looked completely wrong to me.

[bubsy]

for question 19 i said A beacuse the reactants ARE stored within the fuel cell regardless of whether it is pumped continuously. all the other possible answers were plain wrong...so yeah.
hope i'm right.
i said biochemical was more sustainable cos its renewable?

they aren't stored. they are PUMPED IN - hence they were never originally stored in the cell. but i repeat, ALL ANSWERS WERE WRONG FOR Q19

THis is what i think.
Technically electrons do pass from the reductant to the anode though? Anode is just negative electrode?

Reductant (site of oxidation) is the anode. How the hell do electrons go from anode to anode.

LOL that post cracked me up. its A guys.  :2funny:

Dont think so  Its clearly C

for question 19 i said A beacuse the reactants ARE stored within the fuel cell regardless of whether it is pumped continuously. all the other possible answers were plain wrong...so yeah.
hope i'm right.
i said biochemical was more sustainable cos its renewable?

they aren't stored. they are PUMPED IN - hence they were never originally stored in the cell. but i repeat, ALL ANSWERS WERE WRONG FOR Q19

THis is what i think.
Technically electrons do pass from the reductant to the anode though? Anode is just negative electrode?

Reductant (site of oxidation) is the anode. How the hell do electrons go from anode to anode.

LOL that post cracked me up. its A guys.  :2funny:

Dont think so  Its clearly C

um the reductant is the anode.... so it's clearly not C

I don't think the reductant has to be the anode. The anode could be an inert electrode and the reductant could be a species in the solution.

[bubsy]

RAWR. For the stupid liquid phosphoric acid question I didn't realise that it was liquid. I cited temperature as the reason for the discrepancy between the actual E0 and the predicted E0, except I then went on to say that because H3PO4 was triprotic, the concentration of H+ would be higher than the standard 1M used in the ECS. Do you reckon that'll get a mark, or is it sort of implicit in my explanation that the electrolyte was aqueous. I mean I thought it was at the time but I didn't actually write that down... GIMME MARKS!!!!!

[bubsy]

Ummmmm, guys seriosuly....

For that dilution question the [H+] decreases and the [OH-] OBViOusly INCREASES.

There is à higher concentration of OH Ions in Water than in Acid. Hence à dilution will increase OH conc.

Pls correct me i am wrong

The concentrations of H+ and OH- in water are equal. So if the concentration of OH- increases due to the addition of water, it would make sense that H+ increased correspondingly as well. The degree of self ionisation of water is so negligible that I'm pretty sure the OH- decreases as well as the H+. idk, I could be wrong.

[brett011]

Let's say that the intial concentration of h+ is 0.1. The the concentration of oh- is 10^-14\0.1 which is 10^-13. If the acid is diluted the concentration of h+ decrease to let's say 0.001. This means that the concentration of oh- is 10^-14\ 0.001 which is 10^-11. This shows that as h+ decreases oh increases. I think

[aznanthony]

I found it to be quite easy, according to suggested solutions 18 or 19 on multiple choice

[bubsy]

Christ, someone with brains pls
explain how on earth is it possible to have electrons flow to the anode?

Seriously? Are you really going to get this agro over a one mark multiple choice question? If electrons flow from anode to cathode, they do so through the wire. The electrons don't materialise out of thin air (or thin water, given it was a solution). Oxidation is the loss of electrons and since the anode is the site of oxidation, it seems most sensible to me that the reductant, which is OXIDISED, donates its electrons TO the anode, which then passes it on to the cathode. This is my reasoning, fault it if you will but do so in a civil manner.

I also think that it would be profoundly unfair of VCAA to explicitly state one year that fuel cells are not rechargeable and to then expect students to know that they are theoretically rechargeable and work this into a multiple choice question.

As for the situation with solid iron acting as the anode, I'm not entirely sure about the mechanics of this, but seeing as electrons are delocalised in metals anyway, I would simply assume that the production of electrons during oxidation would still be transmitted through the iron, even if it were itself being oxidised in the process.

I'm not particularly good at chemistry, so I chose the option that struck me as being the most logical.

[bubsy]

What did people get for the balanced complete combustion of benzoic acid???

Fkn balancing too ages!! LOL

Hm i think overall it wasn't too bad, considering i barely studied for it (2 prac exams) and had around 6.5 hrs of sleep. I agree that some questions were weird though.

haha me too, i did six exams and had about 5 hours of sleep, but i also had two spoonfuls of instant coffee mixed with a teeny bit of hot water before my exam... it made me jittery,.

[jasoN-]

for question 8a) is it alright to say "fuel  cells are only ~60-70% efficient, hence less voltage produced"

[cama23]

77/82!

[m@tty]

for question 8a) is it alright to say "fuel  cells are only ~60-70% efficient, hence less voltage produced"

That's basically what I said. "In fuel cells there are energy losses to heat and other forms, thus reducing the voltage produced."

[liv]

What did people get for the balanced complete combustion of benzoic acid???

Fkn balancing too ages!! LOL

Hm i think overall it wasn't too bad, considering i barely studied for it (2 prac exams) and had around 6.5 hrs of sleep. I agree that some questions were weird though.

haha me too, i did six exams and had about 5 hours of sleep, but i also had two spoonfuls of instant coffee mixed with a teeny bit of hot water before my exam... it made me jittery,.

i onbly had two hours of sleep last night...because my brain didn't want to switch off. it then took me ages this morning to understand what the questions were asking...
and then when it came to the balancing....bleurgh.