HSC Chemistry Question Thread

[RuiAce]

Should i only be practicing long response questions rather than short responses?

If you ask me, neglecting short responses will mean you end up being bad at those and over complicating it. I always treated short and long responses differently - short just requires a suitable answer; long requires structure.

(I'll assume short responses excludes calculations here)

But you need to figure out YOUR best studying techniques.

[angiezhang9]

Hey! It's a really good question, and quite a tough one too. Firstly, we need to remember that ionisation is the removal of a hydrogen ion. For weak acids, like acetic acid, this will only occur a small percentage of the time. If we add more water, more acid ions/hydrogen ions will dissociate. This means that the ionisation increases, just because it has more water to react with!

So, we know that there are MORE hydrogen ions in the solution after we add water than before. Why doesn't the pH change? Remember that the formula for pH is -log[H], where [H] is the CONCENTRATION of Hydrogen ions. Whilst the AMOUNT of Hydrogen ions have increased, the amount of liquid has doubled too. Ionisation will only barely increase, so the relative concentration of ions will actually decrease. As such, the concentration of Hydrogen ions will decrease, and thus the pH will increase.

Let me know if this explanation makes sense!

Jake

That was a perfect explanation! Thanks so much Jake

[milkteaOO]

Hi! I was just wondering if anyone could tell me the rules for calculating how many significant figures in something in chemistry? Thank you!

[RuiAce]

Hi! I was just wondering if anyone could tell me the rules for calculating how many significant figures in something in chemistry? Thank you!

This has most likely been answered already in this thread but I can't be bothered digging it up.

Of all of the data (numbers) you use, whichever number has the least amount of significant figures is the amount that you use.


E.g. What volume of O₂ would be occupied by 3.49mol at 25^oC and 100kPa
You would us the formula n=V/V_M with n=3.49 and V_M=24.79L mol^-1
Hence 3 s.f.

[anotherworld2b]

Hi i just wanted ask for some advice my exams are approximately 3 weeks from now but there is a lot of content to recall. Is there a way to effectively and quickly revise  for chemistry? How did high achievers like yourselves prep for exams? I just wanted to see how others approach studying for exams because ive benn spending a lot of time just on stoichimetry.

[ml125]

Hi i just wanted ask for some advice my exams are approximately 3 weeks from now but there is a lot of content to recall. Is there a way to effectively and quickly revise  for chemistry? How did high achievers like yourselves prep for exams? I just wanted to see how others approach studying for exams because ive benn spending a lot of time just on stoichimetry.

I'm sure that by now you're tired of hearing this - but it's always best to go through whole past papers or even just single past exam questions. In between practice exams, particularly for chemistry, I will usually go through specific questions on topics I am less confident in until I feel I can do them properly. What has helped me a lot is that within my notes, I include questions and examples to address any major concepts so I have an easy resource to look back on if I get stuck.

[jakesilove]

Hi i just wanted ask for some advice my exams are approximately 3 weeks from now but there is a lot of content to recall. Is there a way to effectively and quickly revise  for chemistry? How did high achievers like yourselves prep for exams? I just wanted to see how others approach studying for exams because ive benn spending a lot of time just on stoichimetry.

Hey! I totally agree with the above reply. The other thing I would be doing is going through a comprehensive set of notes, and just writing out all of the information you're not comfortable with yet. Be super succinct in your summary, and use colours to structure your notes. Learn from these summary sheets, and cut down on them as you learn the content. Ideally, you want to get these sheets (which you should rewrite everytime you understand something, because then you can take it OFF your sheet) down to like one or two pages by the time the exam comes around.

Other then that, just focus on past papers!

Jake

[anotherworld2b]

Is this the right answer?

Spoiler

In your last line of working, you divide by 0.001 instead of 0.01! The answer should be 0.423M instead of 4.23M. Other than that, the rest should be fine

[anotherworld2b]

I was also wondering is my answer right for these questions ?

[RuiAce]

I was also wondering is my answer right for these questions ?

It's hard to say whether or not you're doing it right for a question like this without seeing all the previous parts.

Also, it's an ask but if you're going to use pencil can you please use a darker one? It's a bit tiring to read at times

[anotherworld2b]

Sorry. I've been trying to so this question for a while but i cant get the right answer 

[MysteryMarker]

Hey guys,

Just curious as to what the syllabus is actually asking for this dot point, 'Compare the properties of the gaseous forms of oxygen and the oxygen free radical.

Like what would I write if this were to come as a short answer question in my exam?

Cheers guys.

[RuiAce]

Hey guys,

Just curious as to what the syllabus is actually asking for this dot point, 'Compare the properties of the gaseous forms of oxygen and the oxygen free radical.

Like what would I write if this were to come as a short answer question in my exam?

Cheers guys.

In terms of reactivity, everyone knows that oxygen is moderately reactive as whilst it doesn't react aggressively by itself, it can be made aggressive through means of burning/combustion and etc.

However, ozone is appreciably more reactive due to the instability of the coordinate bond. It is essentially a site of higher reactivity.

The oxygen free radical is the most reactive due to the fact that it's a single atom. It doesn't even have a full outer shell and wants to fill it up.


Then in terms of melting/boiling points, oxygen is a linear molecule and its melting/boiling points are extremely low

However, the melting/boiling points of ozone are slightly more elevated due to the fact that it is bent. The central oxygen has a lone, unbonded pair of electrons which is a site for dipole-dipole interactions.

[MysteryMarker]

In terms of reactivity, everyone knows that oxygen is moderately reactive as whilst it doesn't react aggressively by itself, it can be made aggressive through means of burning/combustion and etc.

However, ozone is appreciably more reactive due to the instability of the coordinate bond. It is essentially a site of higher reactivity.

The oxygen free radical is the most reactive due to the fact that it's a single atom. It doesn't even have a full outer shell and wants to fill it up.


Then in terms of melting/boiling points, oxygen is a linear molecule and its melting/boiling points are extremely low

However, the melting/boiling points of ozone are slightly more elevated due to the fact that it is bent. The central oxygen has a lone, unbonded pair of electrons which is a site for dipole-dipole interactions.

Oh thanks, but I was asking for the differences between oxygen and the oxygen free radical, not oxygen and ozone haha.

Cheers.

[jakesilove]

Oh thanks, but I was asking for the differences between oxygen and the oxygen free radical, not oxygen and ozone haha.

Cheers.

Really, the main points I would know are where they are found (ie. radicals are largely in upper atmosphere, as they are very unstable etc.), their comparative reactivities and their chemical structures. You'll never be asked more than three marks on it (tbh you'll never be asked on this at all). Potentially, you can discuss each of their importance.

Jake