HSC Chemistry Question Thread

[RuiAce]

For Q 18 of the 2010 paper, why is the answer C?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2010exams/pdf_doc/2010-hsc-exam-chemistry.pdf

For D : When the Ammonium and Chloride dissociate, wouldn't the positively charged ammonium ion ionise with the hydroxide in the water, creating water and ammonia?

And for HSC 2006 Q8, given that they have the same concentration, wouldn't that mean that they are equally dilute/concentrated?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2006exams/pdf_doc/chemistry_06.pdf

So I'll assume that you figured out why A and B are wrong (neutral salts).

Be careful as to which is the conjugate acid and which is the conjugate base here. H⁺ is the conjugate acid of H₂O

Yes, soon enough you'll have NH₃ and what not forming but what happens at the start? What you're adding isn't NH₃, it's NH₄Cl. That's the first thing that comes into contact with the mixture

When the ammonium chloride dissociates, the NH₄⁺ will rush to react with the H₂O already there. This causes the equilibrium to shift to the RIGHT (as per LCP), which is what we DON'T want here.


Instead, by adding sodium acetate, the CH₃COO^- will rush to react with the H⁺ instead. This forces the equilibrium to shift to the left to produce the chromate ions that we do want.

[RuiAce]

For Q 18 of the 2010 paper, why is the answer C?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2010exams/pdf_doc/2010-hsc-exam-chemistry.pdf

For D : When the Ammonium and Chloride dissociate, wouldn't the positively charged ammonium ion ionise with the hydroxide in the water, creating water and ammonia?

And for HSC 2006 Q8, given that they have the same concentration, wouldn't that mean that they are equally dilute/concentrated?

https://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2006exams/pdf_doc/chemistry_06.pdf

In question 8 they don't have equal concentrations. Acid X is 0.1mol L^-1 and acid 2 is 1 mol L^-1. So the second is more concentrated than the first because 1 > 0.1

[RuiAce]

Hi, this 2005 question has the answer as B, which i agree with. However i don't understand why option D is wrong, do electrons not flow through the voltmeter? Thanks in advance

Because we can't "observe" it per se. Observe means that we see it happen.

A bit silly lol

[lha]

Use the raw marks database to see historic data.

What is reported exam mark?

[RuiAce]

What is reported exam mark?

The first two columns are pretty much the same thing. It's just that because some options are harder they get a tiny bit scaled (usually at most +1 mark).

Treat the first column as accurate in my opinion, and compare it to the last column.

[lha]

The first two columns are pretty much the same thing. It's just that because some options are harder they get a tiny bit scaled (usually at most +1 mark).

Treat the first column as accurate in my opinion, and compare it to the last column.

So is the last column the scaled hsc mark?

[RuiAce]

Hey for this, I understand it's an exothermic reaction so the answer can be B or D only but how is the answer D? Do we look at the moles or something?


(Image removed from quote.)

Pressure is going to play a role here.

Observe that in reaction B, there are EQUAL moles of gas on the reactants and the products. This means that, if we should vary the pressure, it should NOT affect the position of the equilibrium, and thus the yield of product.

Whereas in equation D, there are MORE moles of gas in the reactants than on the products. If there are more moles of gas in the reactants, then higher pressures should FAVOUR the FORWARD reaction, and thus the yield is increased.

Which is what is demonstrated, so the answer is D.

So is the last column the scaled hsc mark?

Yeah, basically

[kimmie]

Do we need to know the formula for cyclohexane and bromine water? Or just cyclohexene and bromine water?

[RuiAce]

Do we need to know the formula for cyclohexane and bromine water? Or just cyclohexene and bromine water?

The reaction between cyclohexane and bromine water is similar.

It's just that:
a) You have to write UV on top of the arrow, cause otherwise the reaction doesn't happen
b) H₂ gas is also produced

So it doesn't hurt to know that extra bit extra

[kimmie]

So like this?

[RuiAce]

So like this? (Image removed from quote.)

Yep excellent

[bethjomay]

"identify a range of salts which form acidic, basic or neutral solutions and explain their acidic, neutral or basic nature."

For this dot point, where it says explain do we just need a chemical equation demonstrating it behaving as an acid/base?

[RuiAce]

"identify a range of salts which form acidic, basic or neutral solutions and explain their acidic, neutral or basic nature."

For this dot point, where it says explain do we just need a chemical equation demonstrating it behaving as an acid/base?

Well you need to be able to relate to your equation properly.

Take something like sodium carbonate. It's basic because of the behaviour of the carbonate ion in water:
CO₃^2- + H₂O_(l) <-> HCO₃^- + OH^-

(Alternatively show how it reacts with an acid.)

But so long as you know how to refer to your equation then yeah you're all good.

[bethjomay]

Well you need to be able to relate to your equation properly.

Take something like sodium carbonate. It's basic because of the behaviour of the carbonate ion in water:
CO₃^2- + H₂O_(l) <-> HCO₃^- + OH^-

(Alternatively show how it reacts with an acid.)

But so long as you know how to refer to your equation then yeah you're all good.

Yep, that's what I have! Thank you!

[MysteryMarker]

Just a generic question, but for a question on 'Assess the effectiveness of AAS in pollution control', what would be some main points to talk about?

Cheers.