VCE Chemistry Question Thread

[sweetiepi]

ether linkage is

R-O-R'

so don't include the carbons since it really can be anything

An ether link is usually C-O-C though, I'd circle just in case

OP should consult their teacher, just in case ^_^

[Sine]

An ether link is usually C-O-C though, I'd circle just in case

OP should consult their teacher, just in case ^_^

that's true. It's one of those ambigious ones, when I have some substantial free time I'll look through some past exams for a precedent 

[ponphi]

If a link results from a condensation reaction, it should be the remains of the two functional groups after the small molecule has been eliminated.
Carboxyl + hydroxyl gives -COO-  ester link
Carboxyl + amino gives -CONH-   amide link
Hydroxyl + hydroxyl gives -O-       ether link

[usernameincorrect]

Hello! Can anyone who has done their food chemistry SAC please share what might be on/the format of how you school had it? Any info really cheers

[Bri MT]

Hello! Can anyone who has done their food chemistry SAC please share what might be on/the format of how you school had it? Any info really cheers

On our SAC we had to:
-Draw a possible structural formula of an omega 3 fatty acid when given the molecular formula
-Complete energy calculation based on nutritional packaging info
-Explain why different foods had different energy despite same/simlar total mass
-Explain why acidity might cause lump formation in sour milk with reference to proteins (ie enzyme denaturation)
-Rank foods in order of GI and explain our choices
-describe differences in protein content of a plant based and animal based food ( essential amino acids)
-identify rancidity prevention techniques
-identify from a list, what foods are more likely to become rancid
-describe differences between sat and unsat fatty acids
-probably more than I'm forgetting

[usernameincorrect]

On our SAC we had to:
-Draw a possible structural formula of an omega 3 fatty acid when given the molecular formula
-Complete energy calculation based on nutritional packaging info
-Explain why different foods had different energy despite same/simlar total mass
-Explain why acidity might cause lump formation in sour milk with reference to proteins (ie enzyme denaturation)
-Rank foods in order of GI and explain our choices
-describe differences in protein content of a plant based and animal based food ( essential amino acids)
-identify rancidity prevention techniques
-identify from a list, what foods are more likely to become rancid
-describe differences between sat and unsat fatty acids
-probably more than I'm forgetting

Woah that sounds like a lot, thanks so much!

[syubi]

In calorimetry questions where you work out the enthalpy of the reaction which involves volumes of acids, do we work out the mass of the solution by using the density of water in the data book (0.997g/mL)?

[Syndicate]

In calorimetry questions where you work out the enthalpy of the reaction which involves volumes of acids, do we work out the mass of the solution by using the density of water in the data book (0.997g/mL)?

Yes

[anotherworld2b]

I don't really understand why the integer ratio is x3 . Where did 3 come from?

[Sine]

I don't really understand why the integer ratio is x3 . Where did 3 come from?

they are converting the mole ratio to a integer
since one of the numebrs has a .67 it can eb easily seen that we are required to multiply by 3 to get to an integer number

e.g. if we had .33 we would multiply by 3
if we had .25 multiply by 4
if we had .50 multiply by 2

[-273.15]

Hi guys!
For VCAA 2015 exam question 10bii (see screenshot attached), it asks to label the electrodes (i.e. if it is MH or NiOOH)
The polarity of the electrodes are given and so are the half equations for the anode and cathode
however I am confused because I'm unsure if the polarities labelled on the diagram are for the recharging or discharging reaction
I assume because the reactions given are for recharging, the polarities represent this but the question is in between other questions in relation to discharging so I wasn't sure which one to go with

Could someone please help
thank you

[Rieko Ioane]

Hi, could I have some clarification it's stuff in the book.

They say "denaturation is a result of the disruption of interactions between side chains of the amino acids and the amide links", so they are saying that there a intermolecular forces between side chains with the amide links or are they saying intermolecular forces with side chains with side chains and amide links with amide links?

I thought only the side groups played a role in creating the tertiary structure, not the amide links?

Also, are hydroxyl groups in organic compounds neither basic or acidic? So they won't react at the extremes of the pH scale?

[Phenomenol]

Hi guys!
For VCAA 2015 exam question 10bii (see screenshot attached), it asks to label the electrodes (i.e. if it is MH or NiOOH)
The polarity of the electrodes are given and so are the half equations for the anode and cathode
however I am confused because I'm unsure if the polarities labelled on the diagram are for the recharging or discharging reaction
I assume because the reactions given are for recharging, the polarities represent this but the question is in between other questions in relation to discharging so I wasn't sure which one to go with

Could someone please help
thank you

You're right, there certainly is a bit of ambiguity here. However the potentials of the electrodes DO NOT swap between recharge/discharge - only the reactions do. So either way you should label the diagram the same way.

In the case of discharge, the positive electrode is the cathode (NiOOH). The negative electrode is the anode (MH).

In the case of recharge, the positive electrode is the anode (NiOOH). The negative electrode is the cathode (MH).

Hi, could I have some clarification it's stuff in the book.

They say "denaturation is a result of the disruption of interactions between side chains of the amino acids and the amide links", so they are saying that there a intermolecular forces between side chains with the amide links or are they saying intermolecular forces with side chains with side chains and amide links with amide links?

I thought only the side groups played a role in creating the tertiary structure, not the amide links?

Also, are hydroxyl groups in organic compounds neither basic or acidic? So they won't react at the extremes of the pH scale?

Denaturation involves the disruption of both the secondary (regular H-bonding between amide links) and tertiary (side chain interactions) structure. So the textbook addresses both separately in that one sentence.

For what you need to know, hydroxyl groups are neither acidic nor basic and therefore are not affected by pH. (in reality they can be both protonated and deprotonated under the right conditons but this is entirely outside of the study design and you best forget I ever mentioned it )

[usernameincorrect]

Ive come across some questions about acid base reactions in 2016 practice papers, as well as Ka calculation. Is this stuff from the older study design, and do we need to know it? Same for fermentation reactions as well. Also, are unit 1/2 stuff that isn't covered in 3/4 examinable by VCAA? Thanks!

[Syndicate]

Ive come across some questions about acid base reactions in 2016 practice papers, as well as Ka calculation. Is this stuff from the older study design, and do we need to know it? Same for fermentation reactions as well. Also, are unit 1/2 stuff that isn't covered in 3/4 examinable by VCAA? Thanks!

I don't think you have to know the acid-base stuff (can't say 100% though). If I am correct the only fermentation reaction you have to know is the fermentation of glucose (by bacteria in an digester) to produce bioethanol and CO2.