VCE Chemistry Question Thread

[Maya24]

Can someone help me out with vcca 2014 Q9a?  Shouldn't cl go under reduction at the cathode as it is the strongest oxidant? Thanks in advance

[sweetcheeks]

Can someone help me out with vcca 2014 Q9a?  Shouldn't cl go under reduction at the cathode as it is the strongest oxidant? Thanks in advance

Are you talking about chlorine gas that is produced by the reaction? If so, the inert gas displaces any chlorine produced to remove it from the system so it doesn't react with the magnesium or the cathode.

[Maya24]

For the 2018 NHT chemistry exam Question 1, how come compound T is not a carboxylic acid. As s reacts with cr2o7^2-, shouldn't  T become a carboxylic acid? Thanks in advance.

[Bri MT]

For the 2018 NHT chemistry exam Question 1, how come compound T is not a carboxylic acid. As s reacts with cr2o7^2-, shouldn't  T become a carboxylic acid? Thanks in advance.

S is oxidised from an alcohol to a ketone.

If the location of the alcohol was different, then it could be oxidised to an aldehyde, which could be oxidised to a carboxylic acid.


Edit: typo (again)

[Azzzz]

For the 2018 NHT chemistry exam Question 1, how come compound T is not a carboxylic acid. As s reacts with cr2o7^2-, shouldn't  T become a carboxylic acid? Thanks in advance.

Compound T is pentan-2-ol which means it is a secondary alcohol (the carbon the OH group is attached to is attached to 2 other carbons). When oxidized secondary alcohols become ketones rather than a carboxylic acid. This is due to the hydroxyl group not being at the end, primary alcohols when oxidized turn into aldehydes then can be oxidised to carboxylic acid's as the hydroxyl group is at the end of the molecule (and carboxylic acids are always at the end of molecules) while tertiary alcohols cannot be oxidized, due to the carbon which the OH is attached to is also attached to three other carbons, when an alcohol is oxidized it forms a double bond. The three already carbons which are already present take up the four bonds that the OH's carbon already has.

[Maya24]

I'm struggling with the vcca electrolysis/galvanic redox equations. Does anyone have any tips on how I can improve?

[Azim.m]

What method could be used to produce PURE propyl propanoate? (Besides fractional distillation) 

[sweetiepi]

What method could be used to produce PURE propyl propanoate? (Besides fractional distillation) 

Fractional distillation is the main method to purify esters, however in lab I have done liquid-liquid extractions for esters not miscible in water. You can also do simple and steam distillations (likely not viable options), however these are not covered in the VCE SD* afaik.
(*feel free to correct me on this)

[sweetcheeks]

What method could be used to produce PURE propyl propanoate? (Besides fractional distillation) 

Some forms of chromatography (column, HPLC).

[rinner]

hey can anyone clarify how an antioxidant works against oxidative rancidity?
Does it a) react preferentially with oxygen in air, hence reducing the extent of oxidation of unsaturated fatty acids
or b) prevent propagation of free radicals?
thanks in advance!!

[sweetiepi]

hey can anyone clarify how an antioxidant works against oxidative rancidity?
Does it a) react preferentially with oxygen in air, hence reducing the extent of oxidation of unsaturated fatty acids
or b) prevent propagation of free radicals?
thanks in advance!!

Most work antioxidants work by donating a hydrogen atom radical to other radicals, preventing them from reacting with nearby molecules.

(Extra) A little bit of stuff from a unit I had this semester

Antioxidants work in two ways:
Type 1. Sacrifice antioxidants have a lower electrochemical oxidation potential and are more easily oxidised than the active substance that is being protected.
E.g., Vitamin C, hydroquinone

Type 2. Chain terminating antioxidants generate low concentrations of stable free radicals that interfere with the progress of oxidation reactions by reacting with essential free radical intermediates in the reaction.
E.g., Vitamin E, melatonin

[Freddie Hg]

Most work antioxidants work by donating a hydrogen atom radical to other radicals, preventing them from reacting with nearby molecules.

(Extra) A little bit of stuff from a unit I had this semester

Antioxidants work in two ways:
Type 1. Sacrifice antioxidants have a lower electrochemical oxidation potential and are more easily oxidised than the active substance that is being protected.
E.g., Vitamin C, hydroquinone

Type 2. Chain terminating antioxidants generate low concentrations of stable free radicals that interfere with the progress of oxidation reactions by reacting with essential free radical intermediates in the reaction.
E.g., Vitamin E, melatonin

hey just checking your extra stuff. we dont need to no that?/

[sweetiepi]

hey just checking your extra stuff. we dont need to no that?/

I don't believe it's in the study design. It's just extra, hence my (extra) tag

[Freddie Hg]

I'm struggling with the vcca electrolysis/galvanic redox equations. Does anyone have any tips on how I can improve?

what seems to be the exact problem with redox?

[ilikenoodlez]

what exactly are we supposed to know in regards to fuels? do we have to know the process of how fossil fuels and biofuels are produced?