VCE Chemistry Question Thread

[HopefulLawStudent]

No, they're not technically the same; I'd stick with "vaporised". Regardless of which word you use, however, your answer doesn't actually explain WHY molecules with a molar mass of greater than 300 g mol^-1 often cannot be analysed by GC. I would write something like "Because often such molecules cannot be vaporised in a gas chromatograph without decomposing". 

Thanks jyce!

[HasibA]

need some opinions for chem
1) should i do prac exams, find what i dont know , and rinse and repeat until my scores average out higher ?
Or
should i do prac exams, revise the whole course lightly, and then continue to do prac exams to find gaps in knowledge?
just wanted some 2cents from past students as to what would be more effective with the time i have left ty !!

[Sine]

need some opinions for chem
1) should i do prac exams, find what i dont know , and rinse and repeat until my scores average out higher ?
Or
should i do prac exams, revise the whole course lightly, and then continue to do prac exams to find gaps in knowledge?
just wanted some 2cents from past students as to what would be more effective with the time i have left ty !!

not a past student lol

some reason i feel both your methods are quite similar so can't really "choose" between them

Personally i was doing prac exams and noting down mistakes and in the past couple of days i went though (just read through) all my Unit 3 notes and a bit more in depth into the stuff i know for sure isn't my best(biofuels). I will probably do this for Unit 4 over the next few days, having said that, i am continuously doing prac exams during this time.

If you don't mind what are your averages this may be a better gauge of what you should be doing

[sweetcheeks]

The answer is A and I understand that, but couldn't C also be an acceptable answer? Isn't it just asking the same thing?

[zsteve]

The answer is A and I understand that, but couldn't C also be an acceptable answer? Isn't it just asking the same thing?

And I'd agree there :/ not sure what's going on. If it's a commercial paper, I'd just ignore it haha. Dodgy question.

[nadiaaa]

For this question, they said the answer was B but in their working out they said the delta H = -250 and the EA = 250
SO just need a bit of help
thanks

[HasibA]

For this question, they said the answer was B but in their working out they said the delta H = -250 and the EA = 250
SO just need a bit of help
thanks

working out must be wrong ? I see no faults with the answer being b. Products minus reactants would give -350 and to go from 250kj to 450kj , 200kj is needed.

[nadiaaa]

Yep alright, just wanted to clarify thank you!

[blacksanta62]

Could anyone explain the steps involved in the formation of biodiesel please
Thank you

[sweetcheeks]

Could anyone explain the steps involved in the formation of biodiesel please
Thank you

In VCE, we just need to know the simplified pathway (there is a multistep mechanism but we just need to know the initial and final steps)

Take a triglyceride and put it in an aqueous solution containing methanol and a base catalyst (generally sodium hydroxide). The ester link between the glycerol and the fatty acids will be broken, forming glycerol and three fatty acids. The methanol will then react with these free fatty acids and form and ester. This methyl ester is the biodiesel.

You will end up with two layers in the beaker. There will be an aqueous layer which will contain the base catalyst, glycerol, methanol and triglycerides/free fatty acids
The other layer will contain the biodiesel.


Is there anything specific that you are having trouble with?

[larissaaa_]

How do you convert units of pressure and does vcaa expect us to do it on the exam? My teacher has never mentioned how to do it in class and I can't get my head around it.

[HasibA]

How do you convert units of pressure and does vcaa expect us to do it on the exam? My teacher has never mentioned how to do it in class and I can't get my head around it.

unitsof pressure? so 1ATM= 101.3kPa=760mmHg etc. ? just know the basic conversions, and use ratios (i.e if 1ATM= 101.3kPa, then 202.6 kPa must equal....)
make sense?

[nadiaaa]

Hi again,
i just need help with this question as well..
I know that Electrochemical Series is only valid @ SLC but im still struggling to understand this Q.

[larissaaa_]

unitsof pressure? so 1ATM= 101.3kPa=760mmHg etc. ? just know the basic conversions, and use ratios (i.e if 1ATM= 101.3kPa, then 202.6 kPa must equal....)
make sense?

Yess! So for example say we need the pressure to be in kPa for the general gas equation, but the question tells us that the pressure is 3 atm, we just need to multiply 101.3 x 3 ?

[sweetiepi]

Hi again,
i just need help with this question as well..
I know that Electrochemical Series is only valid @ SLC but im still struggling to understand this Q.

Hey!
So to get delta H, you subtract the inital energy from the final energy (in this case   -100-250)

Activation Energy is calculated by the peak energy (450) minus the reactant energy (250). You should get answer B