2010 VCAA Chemistry U4 Suggested solutions

[ghadz7]

cool, sorry i just never eard it called oxide b4 :p

also, u reckon they'll cut mc19 outta the exam?

Why would they do that?

The question was fine?..

How'd you go m@tty? Full marks?

[mirra250]

also pretty sure 8 is A, dilution decreases ocncentration of all ions - just because hydronium ion conc decresases doesnt necessarily mean OH- increases...

Why not? I always thought if one increases, the other decreases.

Dilution decreases ALL concs... nuff said? you can't dilute parts of your solution. why is there even debate about this

Jess Christ.....

Pure water has a higher concerration on OH ions than an acid. So when mixed, the end solution will have an overall increased concentration of OH.

Surely ppl dd not forget about the OH concentration in pure water.

Besides the concentration of H+ ions and the concentration of OH ions needs to multiply to give A fixed value at a fixed temperatre. Temp was fixed in question....

Therfore is concentration of H+ ions decreases concentration of OH ions must increase if temp is kept constant.

Finally someone gives a proper explanation!

[m@tty]

cool, sorry i just never eard it called oxide b4 :p

also, u reckon they'll cut mc19 outta the exam?

Why would they do that?

The question was fine?..

How'd you go m@tty? Full marks?

Lol man.. I haven't spotted any errors yet.. :buck2: I think I did decently

EDIT: I got one MC wrong so far...

[Mao]

Why doesn't the Li+ move to the left?? I thought it would finish the 'circuit' by doing so....feel free to correct me :S

As the cell discharges, the reaction at anode is LiC6 --> C6 + Li+(electrolyte) + e, so Li+ is being discharged from LiC6 into the electrolyte, movement to the right.

To 'complete' the circuit, you need a NEGATIVE charge to 'complete' the circuit in the same direction, or a positive going in the opposite direction.

[vexx]

Ammonia

a)i) 3H2 + N2 <--> 2NH3
ii) porous iron catalyst (Fe2O3)
iii) provides an alternative pathway with lower activation energy for the reaction to take place.
b)i)highly corrosive, toxic gas
ii) burns skin, lungs, etc...
iii) wearing protective equipment, ventilation

[mustafa]

I disAgree with 19 MC. The anode and reductand are the same.

I acknowledge Mao's argument that electrons flow from the reductant molecule to te anode electrode, but in this case, both are Fe(s) ...,

electrons don't flow from Fe(s) to Fe(s) in a logical VCAA question...
Although Tyne logic of that question is somewhat stupid.

[bomb]

and H2 combusts in the data book at 286 kJ/mol not 289...

Mao, there is an error in Q's 2.1.b ii) The combustion is -286 Kj/mol, not 289


Also for the chosen chemical only sulfuric acid is given   , wouldn't you know of Ammonia as well?

oops. fixing now.

I do know production of Ammonia, but not at the VCE level, so I'd have no idea what you guys know is what I think I know and what I think you know might be completely different to what you think I know about what I think you know. (Got it? )

7b i put lithium has a low Mr and is lightweight...acceptable answer?

[Mao]

electrons don't flow from Fe(s) to Fe(s) in a logical VCAA question...

And fuel cells don't recharge, in VCELand, or real world

[mirra250]

cool, sorry i just never eard it called oxide b4 :p

also, u reckon they'll cut mc19 outta the exam?

Why would they do that?

The question was fine?..

it clearly wasnt and you're deluded if you believe C is correct. It is completely ambiguous and unacceptable for a VCE exam and hence will either be removed or everyone who answered will receive a mark. If you think it's another answer than C, then you're totally wrong

[m@tty]

I disAgree with 19 MC. The anode and reductand are the same.

I acknowledge Mao's argument that electrons flow from the reductant molecule to te anode electrode, but in this case, both are Fe(s) ...,

electrons don't flow from Fe(s) to Fe(s) in a logical VCAA question...
Although Tyne logic of that question is somewhat stupid.

No they're not. One is a reactant, the other is an electrode.

[Souljette_93]

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"

[Mao]

and H2 combusts in the data book at 286 kJ/mol not 289...

Mao, there is an error in Q's 2.1.b ii) The combustion is -286 Kj/mol, not 289


Also for the chosen chemical only sulfuric acid is given   , wouldn't you know of Ammonia as well?

oops. fixing now.

I do know production of Ammonia, but not at the VCE level, so I'd have no idea what you guys know is what I think I know and what I think you know might be completely different to what you think I know about what I think you know. (Got it? )

7b i put lithium has a low Mr and is lightweight...acceptable answer?

Potentially, yeah. Light weight and packs charge is generally a good thing. I'd accept that.


Also, if I have missed the karma to anyone who helped out on making the solution set better, pm me and I will karma.

[10weid]

ok, just asked my dad, who has a medical degree with an additional year of study in chemistry, and topped chemistry at melb university 2 years in a row, he said fuel cells ARE rechargeable,.

[m@tty]

ok, just asked my dad, who has a medical degree with an additional year of study in chemistry, and topped chemistry at melb university 2 years in a row, he said fuel cells ARE rechargeable,.

Last years examiner's report clearly said they were not. On top of that I've never read that they are. And seriously? How can you get the reactions to go backward in there? Split the H2O up?..

[andy456]

Just a question about balancing the benzoic

would it be 1 mark for correct equation
1 mark for correct co-efficients
1 mark for correct delta H