VCE Chemistry Question Thread

[MG226]

My class was never taught about which foods get digested where in the body, I was doing a company paper and it had a question on where a triglyceride will be broken down, are we meant to know this or is it just a dodgy company question?

[lzxnl]

My class was never taught about which foods get digested where in the body, I was doing a company paper and it had a question on where a triglyceride will be broken down, are we meant to know this or is it just a dodgy company question?

I haven't looked at the chemistry study design in that much detail, but given that that's the sort of thing you cover in biology and biochemistry/physiology at university, I'd be heavily surprised if you needed to know that.

Company exams can be dodgy. I've found mistakes in several company exams in the past. Lisachem back in around 2011-2013 was notorious for making incorrect exams. They failed to recognise that KF, the conjugate base of HF (a weak acid as indicated in your data book) would be basic in one exam.

[zxcvbnm18]

Is 100 one sig fig or three sig figs?

[keltingmeith]

Is 100 one sig fig or three sig figs?

Technically, one, but 100. (With the decimal point) is 3. VCAA will typically not be that ambiguous, though, because the teachers start yelling at them.

[Angelx001]

Why do fats & oils have the ability to be oxidised more so than carbohydrates & proteins? Thank you

[keltingmeith]

Why do fats & oils have the ability to be oxidised more so than carbohydrates & proteins? Thank you

Tbh, to try and give you a proper explanation is a bit beyond VCE level. In general (not even close to always), smaller, acyclic molecules are easier to oxidise.

[kalopsia]

VCAA Sample Exam Q. 6c

Glucose is used as the main fuel by the brain and nervous system, and is the preferred source of fuel for most organs and muscles during exercise.
Suggest why athletes may prefer to include foods with high GI values in their diet.

How should I answer this question?

[Willba99]

VCAA Sample Exam Q. 6c

Glucose is used as the main fuel by the brain and nervous system, and is the preferred source of fuel for most organs and muscles during exercise.
Suggest why athletes may prefer to include foods with high GI values in their diet.

How should I answer this question?

"High GI foods release energy quickly and hence would provide the type of instantaneous energy an athlete would search for" - something like that

[lovelyperson]

Can someone please explain me how to write chemical equations for titration reactions? Are there general formula rulesor something like that  - I'm honestly so lost and just rearrange things until I get something that looks right. 

[simrat99]

For the fermentation of glucose into ethanol and CO2, are the states of glucose and ethanol going to be liquid or aqueous? Thanks

[uhoh]

I need 30 for chem for my course prereq and I've been slacking off the whole yr

What do I need to memorise? I know I need to know the what organic compounds turn into what and their catalysts

Anything else?

[kalopsia]

For the fermentation of glucose into ethanol and CO2, are the states of glucose and ethanol going to be liquid or aqueous? Thanks

According to 2016 examination report, the equation should be C₆H₁₂O₆(aq) → 2C₂H₆O(aq) + 2CO₂(g/aq)

[keltingmeith]

Can someone please explain me how to write chemical equations for titration reactions? Are there general formula rulesor something like that  - I'm honestly so lost and just rearrange things until I get something that looks right. 

Depends what kind of a titration - but, since 90% of them are acid-base anyway, I'll work off of that.

Remember: acids are proton donors, bases are proton acceptors. So, all you need to do is move a proton from your acid to your base. Easy. Example, HCl and NaOH:



Now, this isn't quite it. See, this equation doesn't make a lot of sense. But, you should notice that our NaOH now has a water molecule on it (it's just OH2 as opposed to H2O). So, let's remove that:



One final thing that we tend to do here is combine our ions, which tbh is kinda eh, but feel free to do so:



This general process should help you piece through any and all titration questions. Note that this methodology won't always work - not all bases will lose water (some will just exist as a charged species), and some will lose more than just water (try it with NaHCO3 - you should see both H2O and CO2 disappear from that sodium), but if you always to proton from acid to base, you'll always be on the right foot.

[bentennason]

Why do fats & oils have the ability to be oxidised more so than carbohydrates & proteins? Thank you

As stated, the explanation is a tad above your current knowledge. For explanation's sake, however, you can understand the process through your redox fundamentals:
Oxidation is the "addition" of oxygen or the "loss" of hydrogen. Consider a fatty acid which contains a crap load of C-H bonds. Through an oxidative process, you can oxidise these bonds to C-OH and then to C=O (a very wish wash explanation).
With a carbohydrate, you have many more C-OH bonds and so you can only oxidise up "one level" (ie. C-OH to C=O).
With a protein - taking into account all the acidic/basic/cyclic Z chains - you are left with a few aliphatic carbon atoms (CH2,CH3) to oxidise.

So if you sum up the total "oxidations" possible for each of the three biomolecules, lipids will be oxidised to a greater extent than the other two.

[Nicko912]

For an answer of 80.25, would 3 significant figures bring the value to 80.2 or 80.3? Usually I would go 80.3 but there's been some 'even number rounding' rule I've seen on worked answers that rounds down. How do I go about this one ? Thanks