VCE Chem Questions Thread

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 😀

God

Also just randomly, Remember:

For the purpose of the VCE Chemistry Study Design, whole numbers will have the same significant figures as number of digits, for example 400 has three significant figures while 400.0 has four.

This keeps tricking me - lol 😆

N1ck3lGall1um

Hey all,
Quick qs.
Why is can this not be A wouldnt it still force a forward reaction in both reactions.

Dissolved carbon dioxide, CO2, can react with water, H2O, to form carbonic acid, H2CO3.
H2CO3 can also react with H2O to form bicarbonate ions, HCO3
–, and hydronium ions, H3O+.
CO2(aq) + H2O(l) ⇌ H2CO3(aq)
H2CO3(aq) + H2O(l) ⇌ HCO3
–(aq) + H3O+(aq)
A beaker that contains 2 L of deionised water is placed in a room and left overnight so that these two
reactions reach equilibrium. In the morning one change is made to the system.
Which one of the following changes is most likely to result in an increase in the concentration of H3O+ ions?
A. Dilute the solution.
B. Bubble in more CO2 gas.
C. Add a few drops of phenolphthalein indicator.
D. Add a few drops of 0.1 M sodium hydroxide, NaOH, solution.

Correct answer is B

Billzene

N1ck3lGall1um The effect of dilution will be greater than that of any H3O+ produced. However adding CO2 will prompt the system to use it up which favours the side with H+. That's why if you breathe in a paper bag for too long, your blood pH will drop (this is called respiratory acidosis)

Will

While adding water is technically adding a reactant, and should effect the equilibrium, as it is water all it will do is dilute both sides equally, meaning that the concentrations of each are reduced proportionally to each other. Water is not used to determine the equilibrium constant(Kc), so I believe we ignore it when determining which way equilibriums will shift.

I'd appreciate it if other people could confirm

N1ck3lGall1um

Hey all, thanx for your help 😀, but I got another one.

When the battery is fully charged, it has a lead, Pb, anode, a lead(IV) oxide, PbO2, cathode and
a sulfuric acid, H2SO4, electrolyte. When fully discharged, the two electrodes are both coated in
lead(II) sulfate, PbSO4.
Pb(s)(anode), H2SO4(aq)(electrolyte) and lead(IV) oxide PbO2(s) (cathode)
a. i. Write the oxidation reaction, including states, that occurs during discharge:
Pb(s) + H2SO4(aq)  PbSO4(s) + 2H(aq) + 2e–
Pb(s) + SO42–(aq)  PbSO4(s) + 2e–
Can someone please explain why H2SO4 is involved during oxidation .
Cant Pb just oxidise by itself to produce Pb2+

Billzene

N1ck3lGall1um You can't just show Pb as Pb2+ as that implies it's aqueous, whereas in fact you have a precipitate forming ie PbSO4.

Emmy

Hey guys, 1&2 chemistry here, do you have any tips for practical investigation posters? I’m not sure where I’m going with my discussion.
My poster is on a titration to find the concentration of CaCO3 (water hardness) and an evaporation to find TDS, I didn’t get any meaningful results as I didn’t understand how to perform a titration so my results section is suffering too.

Billzene

Emmy I don't understand which technique(s) you're using, it seems like you're using both volumetric and gravimetric techniques?

Emmy

Billzene yes, the experiment had two parts aiming to analyse water quality

Billzene

Emmy what kind of results are you getting? Can you reason what may have caused them in your discussion?

bw304

hey guys! just a question...
when drawing a sequence of amino acids, can you draw each amino acid similar to how it is presented in the data book, or does vcaa expect you to show all bonds? like instead of NH2 doing H-N-H, etc?
tia!!

God

bw304

If it says structural formula, then you have to show each bond. (Which is so painful)

If it just says draw, then no need!

Billzene

bw304 I was told to always draw all bonds even if the data book doesn't show them. VCAA loves rules for thee but not for me

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