VCE Chemistry Question Thread

[Adequace]

For Year 11 and 12 chem is knowing the reactions of alkanes, alkenes, alkynes, alcohols, carboxylic acids and esters important? I had to learn organic chemistry for our mid year exam on my own, so I'm not sure..

Thanks

[Elizawei]

For Year 11 and 12 chem is knowing the reactions of alkanes, alkenes, alkynes, alcohols, carboxylic acids and esters important? I had to learn organic chemistry for our mid year exam on my own, so I'm not sure..

Thanks

I think due to the new course, you guys have to learn organic chem to a more detailed extent
But learning more in yr 11 is good though, since then yr 12 next year will be a breeze for you

[blacksanta62]

The bromine test.
- An unsaturated fat will decolourise a bromine solution due to bromine being added across the C=C bonds in the fat.
- A saturated fat does not have C=C bonds and so no addition reaction occurs and the bromine solution stays its reddish-brown colour.

Just wanted to add this since I thought it was interesting: My teacher said that teachers aren't allowed to do this test anymore because Br2 is carcinogenic in large amounts. Teachers now use I2 when testing for un-saturation.

[Adequace]

Thanks for the reply.

I need help on this question http://m.imgur.com/k0uFJYz

For part a) would it just be that small branched off part on the right? Is the CH3 included?

For part b) I don't understand what to do, what does the circle inside the hexagon ring represent?

[blacksanta62]

Thanks for the reply.

I need help on this question http://m.imgur.com/k0uFJYz

For part a) would it just be that small branched off part on the right? Is the CH3 included?

For part b) I don't understand what to do, what does the circle inside the hexagon ring represent?

A)The ester functional group is the O=C-O-C on the right
B) Circle just represents delocalised (shared) electrons
The synthesis of aspirin is attached. It's a condensation reaction the releases CH3COOH

Edit: I highlighted the ester linkage formed

[jyce]

For Year 11 and 12 chem is knowing the reactions of alkanes, alkenes, alkynes, alcohols, carboxylic acids and esters important? I had to learn organic chemistry for our mid year exam on my own, so I'm not sure..

Thanks

For Unit 1, you need to know how to write combustion reactions for all those families of molecules you mentioned and also how esters are formed from condensation reactions of alcohols and carboxyl acids. You don't know to know about substitution reactions, addition reactions (with the exception of addition polymerisation of alkene monomers) or oxidation of alcohols until Year 12.

[Adequace]

Thanks.

@blacksanta62

Why is the ester functional group including another C-atom? Isn't it just COO?

@jyce

From my understanding of combustion reactions, they always have the products of CO2 and H2O, is this correct and is this all I need to know? In my textbook it only goes over combustion reactions for alkenes and alcohols.

[jyce]

Thanks.

@blacksanta62

Why is the ester functional group including another C-atom? Isn't it just COO?

@jyce

From my understanding of combustion reactions, they always have the products of CO2 and H2O, is this correct and is this all I need to know? In my textbook it only goes over combustion reactions for alkenes and alcohols.

You should be able to write balanced equations for combustion reactions. You'll have an organic compound reacting with oxygen gas, and the products are (almost) always carbon dioxide gas and water/steam.
- First balance the carbon atoms by placing a coefficient in front of CO₂
- Next balance the hydrogen atoms by placing a coefficient in front of H₂O
- Lastly, balance the oxygen atoms by placing a coefficient in front of O₂
If you need x.5 O₂ to balance the equation, multiply all the coefficient by 2 - because you can't have half a molecule.

e.g. Combustion of propanol:
C₃H₈O(l) + O₂(g) -> CO₂(g) + H₂O(l)
Balancing the carbon atoms gives C₃H₈O(l) + O₂(g) -> 3CO₂(g) + H₂O(l)
Balancing the hydrogen atoms gives C₃H₈O(l) + O₂(g) -> 3CO₂(g) + 4H₂O(l)
Balancing the oxygen atoms gives C₃H₈O(l) + 4.5O₂(g) -> 3CO₂(g) + 4H₂O(l)
Multiplying the coefficients by two gives 2C₃H₈O(l) + 9O₂(g) -> 6CO₂(g) + 8H₂O(l)

And yes, you're right: an ester linkage is defined as COO only, not COOC

[JellyBeanz]

Hey guys,

Are we expected to know the processes of cracking? (catalytic cracking)

[blacksanta62]

Hey guys,

Are we expected to know the processes of cracking? (catalytic cracking)

No, my teacher said it was beyond the course.

I was trying to show COO-R but you're right it's just COO- thank you for the correction 

[grindr]

In regards to spectroscopy and chromatography, does VCAA want us to know how these instruments work/function because it says in the study design, 'excluding features of instrumentation and operation'?

[vox nihili]

In regards to spectroscopy and chromatography, does VCAA want us to know how these instruments work/function because it says in the study design, 'excluding features of instrumentation and operation'?

Instrumentation and operation refers to how someone physically actually uses the equipment, not the theory behind them unfortunately.

[HopefulLawStudent]

Could someone please explain this Q to me?

[zsteve]

Could someone please explain this Q to me?

Ok, well remember that retention factor (Rf) is characteristic of the identity of a compound. Judging by the chromatogram, the reaction mixture contains A and B, but not C. So clearly, our reaction either isn't progressing at all OR is progressing REALLY slowly.
C and D are just unfounded assertions (how can we know??) so let's reject those.
Option A is plausible, but a very slowly proceeding reaction basically doesn't occur (i.e. from a molecular point of view, all reactions do proceed, just to a very tiny extent OR very slowly, e.g. rusting of iron)

So I'd go for option B, but it's quite a tricky question to be honest.

[HopefulLawStudent]

Ok, well remember that retention factor (Rf) is characteristic of the identity of a compound. Judging by the chromatogram, the reaction mixture contains A and B, but not C. So clearly, our reaction either isn't progressing at all OR is progressing REALLY slowly.
C and D are just unfounded assertions (how can we know??) so let's reject those.
Option A is plausible, but a very slowly proceeding reaction basically doesn't occur (i.e. from a molecular point of view, all reactions do proceed, just to a very tiny extent OR very slowly, e.g. rusting of iron)

So I'd go for option B, but it's quite a tricky question to be honest.

Apparently the answer is C...?