2009 exam

[thushan]

hey don't call yourself disgusting vegemite!

[pi]

hey don't call yourself disgusting vegemite!

[charmanderp]

No way man haha. Our Methods cohort has about 250 kids and I'm in the bottom 100 for SACs. I think that negates any comparison :p

You go to Melbourne High.

He doesn't?


AND STOP EDITING MY POSTS THUSHAN! I'm fixing it

Doesn't he? I swear when I met him he was wearing his Melb High uniform...

And pi I wasn't editing your posts, I'm just...um...improving them as to enhance their accuracy.

Pssh, as if anyone from MHS could emulate my fashion sense :p

I love Vegemite!

Moderator action: removed real name, sorry for the inconvenience

[destain]

i can dont worry
and seeing as the smartest people in AN is involved in this post
does the first peak in mass spec always show the molar mass of the compound?

and im still getting some sig figs wrong...I asked my teacher and he said to use the lowest sig figs out of the values i use in my question. So in a way the sig figs i use is not related to the actual wording of the question but instead what values i use whether i take it from the question or it's simply a molar mass. And also what if it is just a mole ratio,and if it is 1:1, i just use the answer of my previous question, what sig figs do i do then? thank you LOL

[charmanderp]

The furthest peak away from 0 shows the mass of the molecular ions, which is the positively charged fragment which contains the entire molecule. So yes, that's the molar mass. Although sometimes you'll have two or more molecular ions peaks due to isotopes of certain elements, usually halogens.

[destain]

oh ok thanks
and also what 'special' equations are there where states are changed from what they normally are?
Like in fermentation, ethanol is aq?
And in combustion is the H20 g or l?

[thushan]

oh ok thanks
and also what 'special' equations are there where states are changed from what they normally are?
Like in fermentation, ethanol is aq?
And in combustion is the H20 g or l?

Yup, ethanol is aq and for combustion, either g or l would be accepted for H2O.

[Mao]

does the first peak in mass spec always show the molar mass of the compound?

Not always. Generally, the peak with the largest m/z is the molar mass, but sometimes you get complete fragmentation and there are no molecular ions. Only sometimes though. (No you don't need to know how or when, just know that you won't ALWAYS get the molecular ion)

[destain]

oh ok thanks (: cause i think that queation asked me for the molar mass from the mass spec graph and i just looked at the first peak, it didnt really give any more info and i wasnt sure if i had to assume the first peak is the molar mass.

and also whats significance does being triprotic have in a titration, does it mean the mole ratio is 3:1? and what is propanone? meant to write a half equation for the oxidation of 2-propanol to propanone

[Mao]

and also whats significance does being triprotic have in a titration, does it mean the mole ratio is 3:1?

If the base is monoprotic, then yes.

and what is propanone? meant to write a half equation for the oxidation of 2-propanol to propanone

It is a ketone. Google is your friend.

[destain]

HAHAHAHAHAHAHA my biffle.

With salicylic acid and acetic anhydride and asprin, if the question comes out in the exam, will they give the structures to you or do you have to memorise them?

Also when do you use the term 'covalent' linkage instead of going into hydrogen bonds etc. I'm not sure if that makes sense but
the phosphate and deoxyribose units condense to form the covalent linkages in the backbone of the DNA
so something like that

[charmanderp]

does the first peak in mass spec always show the molar mass of the compound?

Not always. Generally, the peak with the largest m/z is the molar mass, but sometimes you get complete fragmentation and there are no molecular ions. Only sometimes though. (No you don't need to know how or when, just know that you won't ALWAYS get the molecular ion)

Do you know any examples where that happens?

[jadams]

Thought i'd ask here, given the thread title:

In Q4b of the 2009 exam, I guess I am being very literal, but i gave the number of moles of hydrogen as actual number of moles of H, not H2 as the question requests amount in moles of "hydrogen reacting." I can't possibly see how they could mark that wrong, but no mention of anyone answering as such in the assessor's report.

[Tonychet2]

In a laboratory investigation, a 1.00 g sample of pure myrcene fully reacted with exactly 510 mL of hydrogen gas which is H2 lol but ure right and since its ambiguous they cant assume its only h2 rather than n(h) = 2x n(H2)

or maybe only a small small proportion of people did it <1% of the 10% who got 2 marks lol
 but id assume the 10% who got it  correct would realise itd make more sense to calculate the mols of h2

[jadams]

In a laboratory investigation, a 1.00 g sample of pure myrcene fully reacted with exactly 510 mL of hydrogen gas which is H2 lol but ure right and since its ambiguous they cant assume its only h2 rather than n(h) = 2x n(H2)

or maybe only a small small proportion of people did it <1% of the 10% who got 2 marks lol
 but id assume the 10% who got it  correct would realise itd make more sense to calculate the mols of h2

Obviously its reacting with Hydrogen gas haha...I'm only contemplating the ambiguity and vagueness of the question itself...no chemistry, merely interpretation/logic.