2009 Chemistry Unit 3 Exam Questions and Suggested Solutions

[methodsboy]

^yeah. higher. since some of the Na... would be partly neutralized and hence, making the acid less effective (decreasing its strength). Therefore, a larger volume of the HCl would be used to reach the end point.

[Ilovemathsmeth]

good for me!

[leet]

quote from wiki:

"Typical carrier gases include helium, nitrogen, argon, HYDROGEN and air."

but then:

"Safety and availability can also influence carrier selection, for example, hydrogen is flammable"

probably not the best source out there lol, but i guess the ideas are conflicting?

[avram_grant]

i guess we can complain then

[Lemollin]

That was a really hard paper......

[littlecherry25]

FOR MULTIPLE CHOICE QUESTION 12

SHOULDN'T IT BE C???
 
4 different compounds can be formed......not 3??? MAO, have a look at it again

[NE2000]

FOR MULTIPLE CHOICE QUESTION 12

SHOULDN'T IT BE C???
 
4 different compounds can be formed......not 3??? MAO, have a look at it again

http://vcenotes.com/forum/index.php/topic,14353.msg155765.html#msg155765

[lukeperry91]

Ok, so would H2 have been usable to achieve the chromatogram? Is there even ambiguity on this question anymore? I just asked coblin and he reckons A looks correct at a glance

[lukeperry91]

Wiki's intro to GLC: 'In gas chromatography, the moving phase (or "mobile phase") is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen.'

It only mentions hydrogen in passing in the detailed area on carrier gases. Hydrogen gas isn't listen in textbooks as a carrier gas. WTF

[Ilovemathsmeth]

nah its three because the methyl group thingys are all in the same environment, something i overlooked too during the exam...I HATE FRIKEN VCAA

[huynhvien00]

H2 would give a different chromatogram as the retention times are different due to different rates of adsorption and desorption. H2 molecules are smaller than N2 molecules hence H2 will go through the column faster.

http://pubs.acs.org/doi/abs/10.1021/ac50162a043

[lukeperry91]

huyn thats not answering the question. CAN it be used in this case? and if so is it assumed knowledge for unit 3?

[turley]

for the h2 gas multiple choice thingy

realise the stuff we learn is really simplified down. As if your ever going to get a gas chromatogram with just one clear peak. Anyways, the reason inherts gases are used is so they don't react with the sample. However, i think the question deliberately mentions a "straight chain alkane" to test if we realise H2 gas doesn't react with it (or so says my chem text)

[hard]

get over it guys nothing is gona change

[turley]

thats not true
were assuming mao is right. vcaa could be doing drugs