2010 VCAA Chemistry U4 Suggested solutions

[mirra250]

I'm
sure fuel cells are rechargeable.

Last year the assessors said try ACCEPTED responses saying fuel cells were unrechargeable. Which means they can be recharged, but VCAA was just being nice.

Your tap in the sink can also suck up water, but at no point in their operation will they return water to the dam against the main flow. Same principle.

cool story. clearly completely different

[_henwee]

ARGH CRAP!
I MISSED THE LABELLING ARROW QUESTIONS!!! FML!!!

[ckg93]

also catalyst foro sulfuric is vanadium pentoxide..

That is the same as Vanadium (V) oxide

According to the to my chem teacher, it MUST be PENToxide to get the full mark, however, the PROPER name is Di-vanadium Pentoxide.

I assumed that the dilution by water would decrease both, however was the increase in [OH-] (by adding water) significantly more than the decrease by dilution??? Taking into account 10 ml of 0.01M Hcl WILL have OH- ions already.

[m@tty]

I don't know if it has been contested yet.. But I believe you've got 18 wrong. It was being electrolysed. So the strongest oxidant is oxidised.. I believe that the correct answer is B. The anode reaction is the oxidation of the sulfate ion and the cathode is the reduction of water..

I think you missed that a current was being supplied?

My 18 is B?

I meant A.

Don't you take the highest in the series for oxidation in electrolosis? Thus the sulfate ion?

If it wasn't for the current I agree it would be water oxidised..

[jasoN-]

For short answer 1ai) why put units? this would be doubling up would it not?

[andy456]

I'm
sure fuel cells are rechargeable.

Last year the assessors said try ACCEPTED responses saying fuel cells were unrechargeable. Which means they can be recharged, but VCAA was just being nice.

Are you serious...... read what you wrote...
Accepted responses saying that fuel cells were UNRECHARGEABLE.........that means cannot be recharged

From VCAA's assessment report last year (page 11, answer to 5d.)
Acceptable responses included:
• fuel cells are not rechargeable
• fuel cells needs continuous supply of reactants
• fuels in fuel cells are molecular, not ionic
• products of fuel cells are not recycled
• some fuel cells produce CO2
• fuel cell electrodes are porous.

VCAA is not going to go back on their word

[bomb]

There is NO WAY that could be right.

If it's rechargeable then a CONTINUOUS FLOW OF REACTANTS is not possible, and the REACTANTS WOULD BE STORED, which would make the other answers right.

[Souljette_93]

I don't know if it has been contested yet.. But I believe you've got 18 wrong. It was being electrolysed. So the strongest oxidant is oxidised.. I believe that the correct answer is B. The anode reaction is the oxidation of the sulfate ion and the cathode is the reduction of water..

I think you missed that a current was being supplied?

My 18 is B?

I meant A.

Don't you take the highest in the series for oxidation in electrolosis? Thus the sulfate ion?

I got A, and i also didn't understand your explanation. ( in the solutions )

[m@tty]

I don't know if it has been contested yet.. But I believe you've got 18 wrong. It was being electrolysed. So the strongest oxidant is oxidised.. I believe that the correct answer is B. The anode reaction is the oxidation of the sulfate ion and the cathode is the reduction of water..

I think you missed that a current was being supplied?

that was incoherent but nonetheless incorrect. an oxidant is REDUCED, a reductant is OXIDISED. In this reaction, water is the strongest reductant hence is oxidised

All half equations in the ECS can go either backward or forward. I know that what I said is technically incorrect, but the species in the half equations higher in the series are often termed as stronger oxidant. The species on both sides. So I guess what I was saying was the weakest reductant will be oxidised.

Looks like you missed that a current was being supplied too :buck2:

[jasoN-]

for short answer 5aii) i wrote "vanadium(II)oxide, V2O5", will i still get the mark? (II instead of V)

[stonecold]

I don't know if it has been contested yet.. But I believe you've got 18 wrong. It was being electrolysed. So the strongest oxidant is oxidised.. I believe that the correct answer is B. The anode reaction is the oxidation of the sulfate ion and the cathode is the reduction of water..

I think you missed that a current was being supplied?

My 18 is B?

I meant A.

Don't you take the highest in the series for oxidation in electrolosis? Thus the sulfate ion?

I got A, and i also didn't understand your explanation. ( in the solutions )

Water is a stronger reductant than what SO42- is...

[m@tty]

But a current was supplied so it was electrolosis. Can someone at least acknowledge that they read that a current was being supplied?

[stonecold]

But a current was supplied so it was electrolosis. Can someone at least acknowledge that they read this?

Yeah, and 2.03 volts is higher than 1.23 volts or whatever water is, so water is the strongest reductant, and will be oxidised...

[m@tty]

But doesn't the current force a reaction which will not normally happen?

Sure, that would happen in a galvanic cell. But it wouldn't also happen during electrolosis, would it?

[vexx]

Ammonia

a)i) 3H2 + N2 <--> 2NH3
ii) porous iron catalyst (Fe2O3)

Isn't it fe3O4?  lol i wrote that and in brackets i wrote "porous iron"

its an iron oxide, the most common one is Fe2O3, but Fe3O4 can be used too just rarer.