VCE Chem Questions Thread

Billzene

Lord I don't think you need to in the new SD. If you're curious, it's M + e- ---> M+ + 2e-. Some people choose to show it with a radical ie M+. but I don't

sasushi

Hey guys I have a question.

So I'm doing a gravimetric analysis task tmr where we have to look at the % of sulphate in fertilizer and compare it to the manufacturer's claim.

One of the steps in the experiment is to grind the fertilizer and then mix it with both HCl and distilled water. Then we boil and add barium chloride to form a precipitate.

I was just wondering what the role of the HCl was.

Billzene

sasushi
A lot of times in fertilisers they also have phosphate in there. Following the solubility rules, barium phosphate is also very insoluble in water, so when you add BaCl2 to the fertiliser which may contain phosphate some Ba2(PO4)3 precipitate may form and you might erroneously include it in the mass of BaSO4 precipitate, which overestimates the sulfate content of the fertiliser. Ba2(PO4)3 is soluble in HCl so adding HCl will prevent it from precipitating such that the final precipitate is exclusively BaSO4

sasushi

Billzene thank you soo muchh!!

Billzene

hamna_fa
You have volume and concentration of the Na2S solution so you want to convert that to mol and then you’d use molar ratios to calculate n(CdS) and hence m(CdS)

Cd(NO3)2 in excess = Na2S is limiting which means the amount of Na2S present (not Cd(NO3)2) is important to know if you want to calculate how much CdS precipitate is produced

God

Hi Billzene!

For VCE purposes; do we need to know how to number carbons in a cyclic molecule?

Eg. For determining if a monosaccharide is alpha or beta?

Thanks in advance 🙏

Billzene

God you need to recognise the structures of alpha/beta anomers of glucose, but you don’t need to know how to name cyclical compounds except maybe benzene

God

Billzene
legend, as always!

Chocolatepistachio

for this question For the boric acid isn’t it 0.89x v1 =1 x 0.15
Stock is C1
But the answer says 133.5g
https://drive.google.com/drive/folders/1qKgLbhtaTwmzOsE-7TBQBFsv-k4HE-xV

Billzene

Chocolatepistachio no idea why it’s in g. Also it should’ve been 0.890 M x v1 = 0.089 M x 0.15 L

PizzaMaster

Hii everyone!
I am so confused...
The answer says 5-bromo-2-chloro-4-ethylhexane
but can't it also be
2-bromo-5-chloro-3-ethylhexane
then which one do you prefer?
Please help Thank you!!!

Ps. I am not sure how to attach the photo

God

PizzaMaster
Click the 'Add an image icon' down below (next to link / dot-points)

Go to and upload ur image to: https://imgur.com/upload

Copy the link from the address bar, and add it in the space provided!

PizzaMaster

sorry that didn't seem to work for me
how about:
https://ibb.co/26R91Z3

God

PizzaMaster
Yeah I see what you mean....

I just tried plugging it into mol-view; which breaks whenever I try to render it / view it's name. Fair chance this molecule doesn't exist... but then again - its chemistry... So who knows.

Maybe Billzene?

Will

What is the accepted equation for alkene hydration?

Is it done with H2 gas? I've read that it is done with steam(H2O) but my textbook says H2(g).
What does VCAA say?

_sophiestudies_

Will
My Edrolo textbook (and what my teacher has taught) says that alkene hydration involves H2O, requiring phosphoric acid and heat as a catalyst (therefore, I'm assuming H2O would be steam due to the heat?). H2(g) is involved in alkene hydrogenation, and needs a metal catalyst (e.g. Ni). Just remember that when you hydrate, you're drinking water, so alkene hydration must involve water (and hydrogenation involves H2(g)). I'm not 100% sure if I'm correct, but that's what I've been taught.

Billzene

_sophiestudies_ this is correct, VCAA said alkene hydration involves H2O(l) on my exam (2018) which was hilariously wrong

God

Hydrogenation: Alkene + H₂ (g) → Alkane: Ni(s)
Hydration: Alkene + H₂O(g) → Alcohol: H₃PO₄ (H₂SO₄ also accepted)

bw304

hi all! i just have a couple quick questions regarding calculations... sorry if these have already been asked!

when you are calculating the specific heat capacity of water, does vcaa expect us to convert mL to grams (as in multiply by 0.997)?

also when finding the percentage atom economy, do you have to take into account the coefficients in the given equation? like if it's 2H2O would you use 2x18 as the molar mass?

sorry if these don't make sense, I've just noticed a slight difference in given solutions across different papers
thanks in advance!!

Christ

bw304
Hello

Q1/ When you are doing calculations involving the equation q=mcΔT, only convert mL to grams if it specifically tells you that the experimental conditions are SLC because the density of water varies with temperature. If conditions are non SLC, then you can just assume mL of water = g of water.

Q2/ Atom Economy takes into account the stoichiometric ratios of the reaction.
SCENARIO
Observe the reaction below, where C is the desired product.
Reaction 1) 5A+5B → C +9D
Reaction 2) 5A+5B→9C+D
It would "make sense" that Reaction 2 has a higher atom economy because greater proportion of the reactants are being converted to the desired product (9C) as compared to Reaction 1, which has a lower atom economy as only 1 C is being produced.

Hope this makes sense 😀

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