HSC Chemistry Question Thread

[conic curve]

Your question is not making sense here. If they're dissolved their already in aqueous state. Aqueous means dissolved in solution.

(Splitting NaCl_(aq) into Na⁺ and Cl^- does nothing. They were always dissolved)

I meant why is it represented that way, with the plus and minus charges?

[RuiAce]

I meant why is it represented that way, with the plus and minus charges?

NaCl_(s) is just solid table salt.

NaCl_(aq) is a shorthand for Na⁺_(aq) + Cl^-_(aq).

If a substance featuring an ionic bond is not dissolved, the fact that the sodium ions and chloride ions are attracted to each other will allow positive and negative (opposite) charges to attract. This forms a sturdy lattice of alternating NaCl molecules.

If a substance featuring an ionic bond is dissolved, a ton of polar water molecules will be attracted to the charged ions. The interaction between the sodium and chloride ions breaks apart due to the interference of the water. There is no longer a true NaCl left being held together; instead a ton of Na⁺ and Cl^- ions are present in the water.

[conic curve]

I'm stuck with the following chemical equations

Zn(s)-->Zn2+(aq)+Zn-. Why is there a "2" there?
Cu2+ + 2e- --->Cu(s) Is this based on charges in the periodic table?

How would you find the net ionic equation of this as an example?

Ca(s)+ZnSO4(aq)--->CaSO4(aq)+Zn(s)

[RuiAce]

I'm stuck with the following chemical equations

Zn(s)-->Zn2+(aq)+Zn-. Why is there a "2" there?
Cu2+ + 2e- --->Cu(s) Is this based on charges in the periodic table?

How would you find the net ionic equation of this as an example?

Ca(s)+ZnSO4(aq)--->CaSO4(aq)+Zn(s)

You don't use the periodic table to determine charges on transitional elements.

They will always specify if the iron ion has a 2+ or 3+ charge. Copper, lead and tin generally have a 2+ charge when unstated. If they say copper has a 1+ charge, or lead/tin has a 4+ charge, then go with that.

The zinc ion has a 2+ charge
The silver ion has a 1+ charge

These are common ones that you need to just know. Just like how you need to know sulfates have a 2- charge.
__________________________

Analyse the species separately watching out for where an electron transfer has occurred:
Ca: It went from solid metal to becoming a calcium ion in calcium sulfate
Zn: It went from being an ion in zinc sulfate to just being a solid metal
SO₄: Nothing happened to sulfate

So you have Ca_(s) + Zn²⁺ -> Ca²⁺ + Zn_(s)

[onepunchboy]

Hi guz , i dont really get this graph question

[RuiAce]

(Image removed from quote.)

Hi guz , i dont really get this graph question

Note how we're talking about rates here.

We know that at equilibrium, the rate of the forward reaction equals the rate of the reverse reaction. I'll assumed you deciphered this part out yourself since you picked A.

We are saying that the equilibrium shifts to the right. This means that the forward reaction is being favoured. Thus, the rate A+B->C is happening is going to be much greater than the rate C->A+B is happening. This is why the answer is B.

Of course, the two graphs collide once the equilibrium has been established.

[conic curve]

In prelim chem, is it possible that they'll assess you on groundwater, even though it's a minor part of the syllabus? (I've never seen a question on groundwater before)

[jakesilove]

In prelim chem, is it possible that they'll assess you on groundwater, even though it's a minor part of the syllabus? (I've never seen a question on groundwater before)

I don't remember anything about the prelim syllabus, but if groundwater is in there, then yes they can assess you on it. If you think that it is unlikely to be tested, just learn it in vague detail, in the event that a question does come up.

[senara]

this is a really generic question but in the case we have to describe an experiment, what exactly do we need to include? because different papers have different marking guidelines :/

[RuiAce]

this is a really generic question but in the case we have to describe an experiment, what exactly do we need to include? because different papers have different marking guidelines :/

The question gives you the aim, so the method that you present them has to address the aim. (Diagram is optional - situationally preferrable)

What do you mean different papers have different marking guidelines? The method is different for every individual experiment. Unless you can post two questions the exact same and their marking guidelines for comparison.

[senara]

The question gives you the aim, so the method that you present them has to address the aim. (Diagram is optional - situationally preferrable)

What do you mean different papers have different marking guidelines? The method is different for every individual experiment. Unless you can post two questions the exact same and their marking guidelines for comparison.

No I mean, some requires safety precautions others variables, discussion etc. and for example a 5 mark question do we need to include everything, for e.g. aim, hypothesis, variables, method, safety...... and so and how would that differ from a 7 mark question (if that makes sense...)

[RuiAce]

No I mean, some requires safety precautions others variables, discussion etc. and for example a 5 mark question do we need to include everything, for e.g. aim, hypothesis, variables, method, safety...... and so and how would that differ from a 7 mark question (if that makes sense...)

Look at the question. If it just says to outline then all they want is a method.

Discussion is almost always asked as a separate question, e.g. assess the validity of your experiment, or e.g. comment on why the calculated E^o value is less than the theoretical.

I do not recall having to include the safety in an experiment unless it actually says to outline the safety. You'll have to provide examples of this. (In fact, I've never heard of a question about an experiment being a 7 marker)

Generally, there's not enough marks for the examiners to give away for you to write a full scientific report on an experiment. Most of the time they just want to see the method or a discussion question as a follow-up.

[senara]

Look at the question. If it just says to outline then all they want is a method.

Discussion is almost always asked as a separate question, e.g. assess the validity of your experiment, or e.g. comment on why the calculated E^o value is less than the theoretical.

I do not recall having to include the safety in an experiment unless it actually says to outline the safety. You'll have to provide examples of this. (In fact, I've never heard of a question about an experiment being a 7 marker)

Generally, there's not enough marks for the examiners to give away for you to write a full scientific report on an experiment. Most of the time they just want to see the method or a discussion question as a follow-up.

Ahh okay.. Thank you

[jakesilove]

Look at the question. If it just says to outline then all they want is a method.

Discussion is almost always asked as a separate question, e.g. assess the validity of your experiment, or e.g. comment on why the calculated E^o value is less than the theoretical.

I do not recall having to include the safety in an experiment unless it actually says to outline the safety. You'll have to provide examples of this. (In fact, I've never heard of a question about an experiment being a 7 marker)

Generally, there's not enough marks for the examiners to give away for you to write a full scientific report on an experiment. Most of the time they just want to see the method or a discussion question as a follow-up.

100% agree with Rui!

[bethjomay]

Hey atar notes! This isn't a specific past paper question, but I was wondering if anyone could give me an accurate/concise version of the reactions involved in CFC's depleting ozone in the atmosphere? I can't seem to find any two sources which agree! Thanks!