HSC Chemistry Question Thread

[Happy Physics Land]

I was wondering would my answer to this question be correct?

PF5 abd PH3 have different shapes because of the structure and cimposition of molecukes each one contains. This determines which intermolecular forces are present,  and these forces determine the physical properties of the material

I also wanted to ask what is the difference between a dipole, polar bond and net dipole?

A dipole is where there is a pair of temporary opposite partial charges on opposite sides of a molecule.
A polar bond is the dipole-dipole interaction (for instance, the partial negative charge on one molecule and the partial positive charge on another molecule) between polar molecules.
A net dipole is essentially just a net partial charge. A substance without a net dipole would often be symmetrical in shape and bondings. A substance with a net dipole would have different electronegativities at the head and tail of the molecule.

[massive]

guys just a quick question, i don't really understand this working out:
For part iii of the q attached, why is the answer just 0.16g/L. Isn't that meant to be 0.16g/100ml and then it becomes 1.6g/L???
thnx

[anotherworld2b]

Hi i was wondering if i could get my current answers checked and get help with the ones left blank.
Also whats the difference between ionisation and dissociation? They seem to be the same thing to me 

[anotherworld2b]

The other part because the attachment was too large

[Happy Physics Land]

Hi i was wondering if i could get my current answers checked and get help with the ones left blank.
Also whats the difference between ionisation and dissociation? They seem to be the same thing to me 

Hey anotherworld2b!

Your colour identification for CuSO4, CuCO3 and potassium manganate are incorrect. CuSO4 should have a blue colour and CuCO3 under normal conditions should have a green colour. KMnO4 is a weird one but it should have a purple colour.

In the context of chemistry, ionisation and dissociation can be used interchangeably, they both mean the splitting up of a compound into its component ions when its in an aqueous form.

[Happy Physics Land]

The other part because the attachment was too large

In your exams I'm sure you wont be asked about most of these chemicals listed in your second post - you are more likely to be asked about the colour of the common types of precipitates. Cr(NO3)3 (chromium nitrate) is usually dark-violet in colour. The mixture of CrCl3 and Mn(NO3)2 is a little more tricky. Basically all it asks you to do is to find the colour of CrCl3 solution and the colour of Mn(NO3)2 solution and find the resultant colour of the mixture of two colours. The colour of CrCl3 is violet and the colour of Mn(NO3)2 is white. So mixing the two colours together, the resulting mixture should be a light purple colour.

[anotherworld2b]

thank you very much for your help
I have another question if that's okay
I am really confused on how to know when to use which concentration unit and how to convert from one to the other?
- %v/v   %w/w and % v/w

Could I get advice before tomorrow? I have a chem test on this tomorrow 

[RuiAce]

thank you very much for your help
I have another question if that's okay
I am really confused on how to know when to use which concentration unit and how to convert from one to the other?
- %v/v   %w/w and % v/w

Could I get advice before tomorrow? I have a chem test on this tomorrow 

That's odd. You're going to have to provide questions that interrelate between %v/v and %w/w

Also dissolution is actually dissolving something. If you dissolve Na₂CO₃ you're not exactly "ionising" because the transfer of electrons has already happened. You're just splitting the molecule apart.

As opposed to reacting sodium with chlorine gas: 2 Na + Cl₂ -> 2 NaCl. This is ionising

[RuiAce]

guys just a quick question, i don't really understand this working out:
For part iii of the q attached, why is the answer just 0.16g/L. Isn't that meant to be 0.16g/100ml and then it becomes 1.6g/L???
thnx

Yeah. They should've just considered concentration in g/L instead of be like mass per litre = ...

[anotherworld2b]

I believe b interrelates %v/v and %w/w but im not sure
How would you tell when to use a particular concentration unit?

[jakesilove]

I believe b interrelates %v/v and %w/w but im not sure
How would you tell when to use a particular concentration unit?

Parts per million is the equivalent of



So, you can relate ppm and %w/w (as mg/kg is w/w, you may just need to convert units!)

[massive]

Guys how do you do this multiple choice question. And also in general how do you decide what electrolyte you want to use??
(the answer is A btw)

[massive]

Guys the answer is D for this question, but couldn't it be A as well???

[jakesilove]

Guys how do you do this multiple choice question. And also in general how do you decide what electrolyte you want to use??
(the answer is A btw)

Hey! For the first question, you just sort of need to know that when you use a platinum electrode (ie. an inert electrode), we generally use a substance like HCl that contains Hydrogen (sometimes, we just use water) which get reduced to form Hydrogen gas. I'm not sure of the best explanation here, except to say that none of the other answers make sense, and we don't have the required metal in the cathode itself.

[jakesilove]

Guys the answer is D for this question, but couldn't it be A as well???

As far as I can tell, the answer could also be A. The equilibrium should shift away from any increase in concentration. Not sure why the answer is D, and not A, although D is definitely correct