VCE Chemistry Question Thread

[keltingmeith]

There will always be ions in the salt bridge. They just stop migrating after the cells stops producing electrical energy. But they are not the reason that the cell stops so the equilibrium is more correct as it is the reason why the cell stops. The ions just stop migrating as a consequence

I don't like this answer - usually, when VCAA says "none of X", they do mean there won't be any.

I think the correct answer is the equilibrium one because you can have galvanic cells where the anode and cathode are in the same beaker - in this case, a salt bridge isn't required. In that sense, lack of ions in the salt bridge doesn't mean the reaction will stop, because they're not always necessary - making the equilibrium answer more correct.

[Daniellac]

I have two questions!

1- with IR spec why does it need to be combined with other techniques?
2- I'm confused about the hydrolysis of DNA, like how many water molecules would be needed to hydrolyise a single and double strand of DNA

Thanks so much! xx

[keltingmeith]

I have two questions!

1- with IR spec why does it need to be combined with other techniques?

You can use IR by itself for complex molecules, actually. BUT IR by itself doesn't give structural information, just for functional groups, so if the molecule is super simple (like, propane), or if you don't have a standard to reference it against, you'll need to use mass spec or NMR to help figure out what you've got.

2- I'm confused about the hydrolysis of DNA, like how many water molecules would be needed to hydrolyise a single and double strand of DNA

Thanks so much! xx

Depends on the length of each strand - you need (n-1) water molecules for n bases.

[Daniellac]

Hey me again aha

Could anyone tell me how many isomers pentene and hexene have, I keep finding different numbers

Thankyou in advance xx

[nadiaaa]

Does consequential marking exist in Chemistry?
Like for the 2015  exam, the question on titration, if you got the mole of HCL wrong obviously all your calculations after would be wrong, so would you just lose all the marks for the rest of the question?? Or can u still gain some marks?

[Samm1]

I don't know what semi-conservative means OR anything about DNA replication, so probably not. The study design only specifically mentions the primary and secondary structures of DNA (primary=sugar-phosphone ester backbone, with four base pairs running along it, made by covalent bonds, secondary=hydrogen bonding between base pairs), as well as the reactions that make them (i.e., condensation reactions. This is the same for all biomolecules you've learned about, btw). Anything else is too much biology for VCAA's liking.

So we don't need to know about Tertiary structures in DNA? That always gives me problems.

[sweetcheeks]

Does consequential marking exist in Chemistry?
Like for the 2015  exam, the question on titration, if you got the mole of HCL wrong obviously all your calculations after would be wrong, so would you just lose all the marks for the rest of the question?? Or can u still gain some marks?

They do give consequential marks. As long as you show the correct working out you will receive marks.

[nadiaaa]

They do give consequential marks. As long as you show the correct working out you will receive marks.

Thank god, thank you!!

[larissaaa_]

I'm confused - are the specifics of sulfuric acid, ammonia, and nitric acid gonna be tested or were they just something we had to do for sac purposes? And aspirin as well?

[keltingmeith]

Just SACs for the first three - but pretttty sure they can ask you about aspirin, VCAA seem to like it. BUT, it's just like a normal esterification, so if you know your pathways, you're good.

[sweetcheeks]

Aspirin is definitely something that can be tested on the exam. It came up in a question last year where you had to draw the functional groups. It gave all the information but it definitely helped if you had seen the process before (we made it at school).

[mandy.healy]

can someone explain to me how to get the anode and cathode equations when the cell is RECHARGING from this overall equation of DISCHARGING. would be greatly appreciated xx 

[mandy.healy]

does glucose have 6 c-H bonds? i keep getting 7 

[The Usual Student]

does anyone know if VCAA will accept
n(r) and n(i)
as moles reacted and moles initial or do I need to say
let n(r) = moles reacted
let n(i) = initial moles

[Adequace]

Hi, does anyone know why all metals can't be analysed by atomic absorption spectroscopy? Thanks.