Exam Suggested Solutions

[sally_hates_school]

i think i need to go bury myself in a hole now :uglystupid2:. if all of mao's answers are right i only got 70%  . mao how did you get all of the questions out of the exam? please dont tell me you had enough time to write it on your data book haha. no seriously. or did you get a teachers copy afterwards or something? OR... can you just plain ask the examiners for it?

i had the opportunity to do both. these are my solutions [in the exam] checked against teacher's solutions after the exam, and except for the "explain" type solutions, the numeric results are pretty all confirmed.

woahhhh, i didnt even have time to read through my answers... but to actually write them out? congratulations you are a GENIUS (not that it would be that hard to be a genius when comparing to me, considering my total inability to READ questions properly lol)

[Aba]

Yeah look at Q2.
It goes.

13.936g -> Diluted to 1000mL -> 25mL Aliquot -> Diluted to 100mL -> sample goes into AAS.

If you find the mol based on that 35mg/L concentration, you can ignore the dilutions, and all you need to do is multiply the mol by to get the amount of mol in the 1000mL, which you then multiply by the molar mass to find the mass of it in the 13.936g sample.

its not dilute to 1000mL

its basically dissolved to 1000mL[yes, there's a step in between, but that step is not quantitative and does not matter, as it is really just dissolving it]

so we can see, only 1 dilution, but it is the 25mL to 100mL, as the concentration of the 25mL aliquot is the same as the 1L solution

hence the dilution factor is 4, not 1000/25, and there is no other dilution taking place. [full stop]

But if you're working with the mol, the dilution from 25mL to 100mL will not affect the answer - there is the exact same amount of mol in both solutions, the concentration is just different! :S.
And in that case, the factor would have to be 1000/25, because even though its dissolved, the volume becomes 1L, and only 25mL of that one litre is actually analysed, so therefor there must be 1000/25 times the amount of mol present then what is actually detected. :S

dilution is dealing with concentraion, bucket. the reading we took from the calibration curve was actually a reading of concentration rather than amount.

if you were dealing with number of mols [not concentration] (i.e. convert 35mg/L to number of mols in 100mL straight away), then your method will be correct. [and will arrive at the same answer]

so my friend is half happy, he may have a slim chance of being right?

if his answer differs from mine, then no, it'll be wrong. however, methodology is not COMPLETELY wrong, he still might squeeze a point or two from it.

Coooolllll, or not, this might mean he beats me !!!!

[sally_hates_school]

Yes that is what I did! I'm not trying to prove you wrong I'm trying to prove aba wrong =_=.
When I saw the concentration as 35mg/L I converted it to mol straight away, and I'm arguing that the dilution factors play no part in it, so hence the double dilution aba is raving on about is irrelevant!

believe me, the question said further diluted. This is their clue for u. (that rhymes)

not that i really want to come into this conversation lol.. but they tend to use words like 'further diluted' to confuse you lol. however the dilution factor was 100ml/25ml im pretty sure

[sally_hates_school]

...im not very good at quoting... so that was a bit weird, edit: and i totally didnt swear on this forum when saying that im not very good at quoting, promise

[Aba]

Yes that is what I did! I'm not trying to prove you wrong I'm trying to prove aba wrong =_=.
When I saw the concentration as 35mg/L I converted it to mol straight away, and I'm arguing that the dilution factors play no part in it, so hence the double dilution aba is raving on about is irrelevant!

not that i really want to come into this conversation lol.. but they tend to use words like 'further diluted' to confuse you lol. however the dilution factor was 100ml/25ml im pretty sure
believe me, the question said further diluted. This is their clue for u. (that rhymes)

They wouldn't say it too confuse us, it was their indication that a double dilution was taking place.

[Aba]

...im not very good at quoting... so that was a bit weird, edit: and i totally didnt swear on this forum when saying that im not very good at quoting, promise

u put some of my quote in urs.

[Aba]

there was a double dilution, it has been confirmed. the top student in the state is now officially Aba's friend

[bucket]

Dude!
The double dilution was irrelevant!!!
I'm positive about this!
They would DEFFINITELY test people on recognising what information is relevant to what you are trying to find!

If you have 0.5mol of something in a 10mL solution, and you dilute it to 100mL, the mol doesn't change! Therefore the dilution is irrelevant!

[sally_hates_school]

Yes that is what I did! I'm not trying to prove you wrong I'm trying to prove aba wrong =_=.
When I saw the concentration as 35mg/L I converted it to mol straight away, and I'm arguing that the dilution factors play no part in it, so hence the double dilution aba is raving on about is irrelevant!

not that i really want to come into this conversation lol.. but they tend to use words like 'further diluted' to confuse you lol. however the dilution factor was 100ml/25ml im pretty sure
believe me, the question said further diluted. This is their clue for u. (that rhymes)

They wouldn't say it too confuse us, it was their indication that a double dilution was taking place.

ok, so 'confuse' wasnt the right word.. but its a way for them to pick out the best students with the best answers kind of thing. they want to make sure that you're really analysing the question and understand everything thats going on.. rather then someone that just memorises "ok so a dilution factor goes like this [insert larger volume/insert smaller volume]"

[sally_hates_school]

...im not very good at quoting... so that was a bit weird, edit: and i totally didnt swear on this forum when saying that im not very good at quoting, promise

u put some of my quote in urs.

nooo but i then put my reply INTO your quote. so... i failed lol

[Aba]

Dude!
The double dilution was irrelevant!!!
I'm positive about this!
They would DEFFINITELY test people on recognising what information is relevant to what you are trying to find!

If you have 0.5mol of something in a 10mL solution, and you dilute it to 100mL, the mol doesn't change! Therefore the dilution is irrelevant!

this is wat they wanted people to think, but the double dilution was everything, u will still get 1 mark on the question and one for the one after thaks to consequential marking

[Mao]

there was a double dilution, it has been confirmed. the top student in the state is now officially Aba's friend

dude, read it properly

the dissolved metal (in nitric acid) was made up to 1000mL (first dilution but not really because it is just dissolving with nitric acid as an agent)

then 25mL of this is further diluted to 100mL (second dilution, and is the only one calculations need to worry about)

hence, your friend is utterly wrong, and is more wrong by assuming he's right

in other words, your friend got tripped out by taking VCAA literally [i'm sure it was there to test people's understanding of back titrations and dilutions]

[Aba]

there was a double dilution, it has been confirmed. the top student in the state is now officially Aba's friend

dude, read it properly

the dissolved metal (in nitric acid) was made up to 1000mL (first dilution but not really because it is just dissolving with nitric acid as an agent)

then 25mL of this is further diluted to 100mL (second dilution, and is the only one calculations need to worry about)

hence, your friend is utterly wrong, and is more wrong by assuming he's right

in other words, your friend got tripped out by taking VCAA literally [i'm sure it was there to test people's understanding of back titrations]

the dissolving and making up to 1000ml is no dilution, but the other parts are, a very well known chemist named 'aba' has come to the conclusion that aba's friend is right,

[bucket]

Meh, believe what you want uhm, 'Aba's Friend', we'll see who was right when we see the statement of results.
Honestly, your calculations make no sense >.< What Sally said was right, they would be trying to test who actually knows when to do what, as opposed to someone who just plugs in formulas.

[Mao]

there was a double dilution, it has been confirmed. the top student in the state is now officially Aba's friend

dude, read it properly

the dissolved metal (in nitric acid) was made up to 1000mL (first dilution but not really because it is just dissolving with nitric acid as an agent)

then 25mL of this is further diluted to 100mL (second dilution, and is the only one calculations need to worry about)

hence, your friend is utterly wrong, and is more wrong by assuming he's right

in other words, your friend got tripped out by taking VCAA literally [i'm sure it was there to test people's understanding of back titrations]

the dissolving and making up to 1000ml is no dilution, but the other parts are, a very well known chemist named 'aba' has come to the conclusion that aba's friend is right,

I now grant you the right to be wrong. but you have COMPLETELY misunderstood the question.