VCE Chemistry Question Thread

[redset8]

The naming is correct. You are correct for the integration as well, its the ratio of the number of protons in each environment.

I'm not too sure.
In the study design it says 'IUPAC systematic naming of organic compounds up to C8 with no more than two functional groups for a molecule, limited to non-cyclic hydrocarbons, haloalkanes, primary amines, alcohols (primary, secondary,
tertiary), carboxylic acids and non-branched esters.'

I guess it wouldn't be any different than a hydroxylated alkene.

Ok thanks heaps sweetcheeks and Billuminati!

With the integration, it is always the ratio, so for example 6:2 is represented as 3:1?

With hydroxylated alkenes, are they like 1-hydroxyl-but-2-ene (or but-2-en-1-ol - I'm not to sure how to name these either)?

[Billuminati]

Ok thanks heaps sweetcheeks and Billuminati!

With the integration, it is always the ratio, so for example 6:2 is represented as 3:1?

With hydroxylated alkenes, are they like 1-hydroxyl-but-2-ene (or but-2-en-1-ol - I'm not to sure how to name these either)?

Yes it's always simplest ratio. If you have another proton environment with 1H, you'll have to keep it as 6:2:1. Note uni chem where u have complex splitting for example in a triplet of quartets (not assessable for VCE), you'll still have to name the subpeak integration ratio 1:3:3:1:2:6:6:2:1:3:3:1. I think the hydroxylated alkene may have been a typo because methene doesn't exist. The alcohol component in your ester is 1,1-methandiol. It's actually a derivative of methanal when it's hydrated by water, but you don't cover this until 2nd year chem.

[redset8]

Yes it's always simplest ratio. I think the hydroxylated alkene may have been a typo because methene doesn't exist. The alcohol component in your ester is 1,1-methandiol. It's actually a derivative of methanal when it's hydrated by water, but you don't cover this until 2nd year chem.

Ooh ok I won't worry about it then. Thanks again Billuminati!

[jasperray]

Hi,
I'm doing an electrolysis prac with a copper anode and inert platinum cathode with the electrolyte copper nitrate. I observed bubbling at an electrode, but I was unsure what this was. Could it be hydrogen gas by the half-equation:
2H2O(l) + 2e– ⇌ H2(g) + 2OH–(aq) ?
How could hydroxide OH- ions be formed if copper nitrate is an acidic solution, and copper ion is a stronger oxidant than water? And could the gas be oxygen instead?

Thank you!

[Billuminati]

Hi,
I'm doing an electrolysis prac with a copper anode and inert platinum cathode with the electrolyte copper nitrate. I observed bubbling at an electrode, but I was unsure what this was. Could it be hydrogen gas by the half-equation:
2H2O(l) + 2e– ⇌ H2(g) + 2OH–(aq) ?
How could hydroxide OH- ions be formed if copper nitrate is an acidic solution, and copper ion is a stronger oxidant than water? And could the gas be oxygen instead?

Thank you!

The gas produced is indeed O2 and your reasoning is correct that OH- can't be produced because Cu(NO3)2 is an acidic salt

Reduction: Cu2+(aq) + 2e- —> Cu(s)
Oxidation: 2H2O(l) —> O2(g) + 4H+(aq) + 4e-

Edited to correct a mind blank

[jasperray]

Thanks for the reply billuminati, but isn't the oxidation reaction Cu(s) -> Cu2+(aq) + 2e- as the anode is copper, and copper is the stronger reductant?
Or is this because at SLC the electrochemical series doesn't hold true?

Edit: I observed gas at the cathode too, so was there gas produced here as well?

[Billuminati]

Thanks for the reply billuminati, but isn't the oxidation reaction Cu(s) -> Cu2+(aq) + 2e- as the anode is copper, and copper is the stronger reductant?
Or is this because at SLC the electrochemical series doesn't hold true?

Edit: I observed gas at the cathode too, so was there gas produced here as well?

Normally you would have Cu oxidised at the anode because you need to replenish Cu2+ concentration in the electrolyte which gets depleted at the cathode to produce solid Cu. My year 12 EPI was on electrolysis of CuSO4 (which is chemically very similar to Cu(NO3)2) with a Cu anode and a graphite inert cathode and the theoretical equations were:

Anode: Cu(s) —> Cu2+(aq) + 2e-
Cathode: Cu2+(aq) + 2e- —> Cu(s)

Your experimental design is very similar to mine. However, you’ve stated that a gas was produced and the oxidation of H2O is the only way to rationalise it. I think you’re looking at a case of non-SLC conditions that may have caused some side reactions. If your anode mass decreased, then oxidation of Cu has definitely occurred and it’s probably best to list the theoretical equations (but also mention the H2O oxidation reaction to give O2)

[jasperray]

The anode mass did decrease, but I agree that oxidation of H2O produced O2 in a side reaction.

Thanks so much Billuminati

[beep boop]

I was wondering if anyone could help with these concentration questions:

a) What volume of  5% m/V cloudy ammonia cleaning solution is needed to make 250mL of a 1.50% m/V solution?
b) What mass of ammonia is present in 150mL of the 1.50% solution?

Thanks in advance!

[Billuminati]

I was wondering if anyone could help with these concentration questions:

a) What volume of  5% m/V cloudy ammonia cleaning solution is needed to make 250mL of a 1.50% m/V solution?
b) What mass of ammonia is present in 150mL of the 1.50% solution?

Thanks in advance!

For a, use c1v1=c2v2: 5 * V1= 1.5* 250, V1= 75mL

For b, remember that 1% m/v = 1g per 100mL, so 1.5%= 1.5g/100mL=  2.25g in 150mL

[Harrycc3000]

Hi guys,
Is an instruments uncertainty (e.g. amp meter uncertainty is plus minus 0.5A) a random error or systematic error or is it none of them?
Thanks!

[Billuminati]

Hi guys,
Is an instruments uncertainty (e.g. amp meter uncertainty is plus minus 0.5A) a random error or systematic error or is it none of them?
Thanks!

The uncertainty in analytical chem actually resulted from a combination of random and systematic error effects

[miyukiaura]

In esterification reactions, I know that H2SO4(l) is the catalyst, however in VCAA reports I've seen that they usually just write H+/H2O. Which one is most correct to write, and would they just accept H+?

Thanks!

[Billuminati]

In esterification reactions, I know that H2SO4(l) is the catalyst, however in VCAA reports I've seen that they usually just write H+/H2O. Which one is most correct to write, and would they just accept H+?

Thanks!

You must write H2SO4(l) or concentrated H2SO4 for VCAA. By the way, it's not appropriate to   conduct esterification in the presence of H2O as it actually causes hydrolysis of any ester formed. Remember that the reaction is an equilibrium reaction and H2O is on the products side so it will not favour the forward reaction. In uni chem we refer to this phenomenon called competing nucleophile in a nucleophilic acyl substitution reaction because H2O as a nucleophile can attack the ester to hydrolyse it back into its components, that's why we use something called the Dean Stark apparatus to remove H2O as it forms in the reaction to both prevent the reverse reaction and to drive the equilibrium towards the forward reaction

[amyzzwq]

Hi,

for mass spec if they ask the fragmentation for the parent ion, do I still have to write + at the back of the ion I give?