VCE Chemistry Question Thread

[Scooby]

Could someone please check if my answers to these questions are correct? Thanks

1. What are the differences between phenol and alcohol?
Phenol is an aromatic organic compound made up of a benzene ring attached to a hydroxyl group, whereas an alcohol is an organic compound containing a hydroxyl functional group.

Presence of a hydroxyl group in a compound doesn't prove that it's an alcohol. The hydroxyl group has to be the principal functional group

[Yacoubb]

Presence of a hydroxyl group in a compound doesn't prove that it's an alcohol. The hydroxyl group has to be the principal functional group

So would I say that an alcohol is an organic with a hydroxyl group as the principal functional group?

I think you also need to show that phosphoric acid actually speeds up the reaction too, although that's easy to prove xP

Why should mass of aspirin increase? Assuming you've filtered and purified your product properly, the catalytic H3PO4 shouldn't be in the aspirin.

Thanks for that. Should I just say that if the mass of pure aspirin obtained has minimal to change as amount of phosphoric acid increases, and if the reaction occurs at a greater rate, this proves that H3PO4 is a catalyst and not in fact a reactant?

Thanks for the help guys!

[Einstein]

out of metallic, ionic and covalent what is the strongest type of bond and why?

thanks

[IndefatigableLover]

Hey AN,

When naming carbon compounds, I know we are required to place a ',' in between numbers (i.e 2,3 dimethyl) but I occasionally see them placed in between numbers and words. So when are we required to use a '-' and ','?

Thanks in advance

Hyphens must separate numbers and letters.
Commas must separate numbers.

[Einstein]

say ive got to elements (making up charges)

Cl^2- and (SO4)2^- , how does the cross over rule work?

[lzxnl]

out of metallic, ionic and covalent what is the strongest type of bond and why?

thanks

That's actually a very dodgy kind of question as technically, all three are variants on the same theme. Ionic and covalent bonds only really differ in how polar the bond is (how large the electronegativity difference is) and metallic, covalent bonds both involve overlap of orbitals.
You don't need to know the above for VCE btw

In terms of the types of bonding commonly seen though, all three types of bonds are strong. It depends on the atoms really. Like, there are very weak covalent bonds (like F-F bonds, will react with almost anything), very weak metallic bonds (think caesium which melts at room temperature) and very weak ionic bonds (look up ionic liquids on Wiki for a list of these). In contrast, there are also strong covalent bonds (diamond), ionic bonds (sodium and lithium fluoride) and metallic bonds (titanium metal). All of these have melting points around or over 1000 degrees.

say ive got to elements (making up charges)

Cl^2- and (SO4)2^- , how does the cross over rule work?

What cross over rule?

[Reus]

say ive got to elements (making up charges)

Cl^2- and (SO4)2^- , how does the cross over rule work?

Cross over rule?

[nhmn0301]

say ive got to elements (making up charges)

Cl^2- and (SO4)2^- , how does the cross over rule work?

You mean for e.g. BaCl2 ( Ba+2 and Cl-1 so swap over to get BaCl2)

[lzxnl]

That's more relying on the fact that the chemical formula for an ionic compound has to be electrically neutral, so you take the lowest integer multiple of the cations and anions and put them together so that the resulting compound is neutral

If this is the case, let's say you have Al 3+ and O 2-
If you have 2 Al 3+ and 3 O 2- you get an electrically neutral compound. Is that what you mean by 'crossing over'?

[Yacoubb]

Is 1:1 ethanol/dichloromethane a polar or non-polar solvent?

[lzxnl]

Likely to be somewhere in-between. I'd say it has a more limited ability to dissolve polar things.

[melbin123]

Help!! How do I do this question
Ans:C

[Sense]

(Image removed from quote.)
Help!! How do I do this question
Ans:C

Remember that in polymerisation a water molecule is lost.

The weight of 4-hydroxyl butanoic acid is 104.

Each monomer will lose h2o so take away the weight of h2o = 104 - 18 = 86

86 x 450 = 38700 

[rinaheartsx3]

Help with part d? My friend thinks the ratio when comparing the acid with bromine is 6:1 but I thought 2:1..explain?

[Rishi97]

Chloroacetic acid is a weak monoprotic acid with a Ka of 1.3 × 10–3 M. For a 1.0 M solution of chloroacetic acid, calculate:
a) the pH
b) the percentage hydrolysis