HSC Chemistry Question Thread

[Cindy2k16]

I got 4.65g, which is closest to B, which is the correct answer. Anyone have an idea why its 5.30g?

dumb question but whats the chemical equation for this reaction? i can't seem to balance it- my mind is still in a post-physics haze lmao

Edit: oh haha nevermind ive got it

another edit: The chemical equation I wrote doesnt work to get the correct answer. I get A instead :/ the mole ratio for Na2CO3, CH3COOH, CH3COONa, CO3, H2O in the equation I wrote is 1:2:2:1:1. Where did I stuff up?

[jakesilove]

dumb question but whats the chemical equation for this reaction? i can't seem to balance it- my mind is still in a post-physics haze lmao

Edit: oh haha nevermind ive got it

another edit: The chemical equation I wrote doesnt work to get the correct answer. I get A instead :/ the mole ratio for Na2CO3, CH3COOH, CH3COONa, CO3, H2O in the equation I wrote is 1:2:2:1:1. Where did I stuff up?

You're totally right, and you're totally wrong; based on research, it looks like the reaction could have been 1:1 OR 1:2. Initially, I actually got what you got, but changed my mind because I knew the answer. Basically, if a reaction could be EITHER 1:1 or 1:2, the HSC just won't assess you on it, because that's totally unfair.

[Cindy2k16]

You're totally right, and you're totally wrong; based on research, it looks like the reaction could have been 1:1 OR 1:2. Initially, I actually got what you got, but changed my mind because I knew the answer. Basically, if a reaction could be EITHER 1:1 or 1:2, the HSC just won't assess you on it, because that's totally unfair.

I don't quite understand what you mean by it can be 1:1 or 1:2.. could u expand on that? TIA

[jakesilove]

I don't quite understand what you mean by it can be 1:1 or 1:2.. could u expand on that? TIA

Only that you can come up with an equation stating that

Acetic Acid + Sodium Carbonate --> Some products

The above reaction is 1:1

2*Acetic Acid + Sodium Carbon --> Different products

The above reaction is 2:1

Both of these equations seem to work, and so it's impossible to tell which one to use! In the HSC, you don't need to worry about that, because only one equation will work.

[noonedoesnt]

Chemistry is so mind crunching

[noonedoesnt]

always get 164 g/mol. Can someone help pls

[grace_joseph]

Hi Jake,

Just wondering if someone could explain to me why ozone is polar? I know it's normally to do with electron distribution but I can't seem to figure this one out. Thanks

[jakesilove]

always get 164 g/mol. Can someone help pls

2*Sodium + 1*Carbon + 3*Oxygen = 2(22.99)+12+3(16)=106g

[Cindy2k16]

Only that you can come up with an equation stating that

Acetic Acid + Sodium Carbonate --> Some products

The above reaction is 1:1

2*Acetic Acid + Sodium Carbon --> Different products

The above reaction is 2:1

Both of these equations seem to work, and so it's impossible to tell which one to use! In the HSC, you don't need to worry about that, because only one equation will work.

Oh I see. Thanks! And what do you mean that only one equation will work? If this was in a long answer question how would you know which one to use?
Actually I believe there was actually a titration question in the HSC in the past that had something similar to this and due to the production of CO2 the titration had 2 equivalence points...Though I think the HSC answer didn't require you to know that lol

[jakesilove]

Hi Jake,

Just wondering if someone could explain to me why ozone is polar? I know it's normally to do with electron distribution but I can't seem to figure this one out. Thanks

Basically, there's a weird number of electrons around a weird shaped object, right? It's configuration will be such that the electrons are as spread out as possible, as they are repulsive. Is it more likely for the 3-Oxygen molecule to be perfectly straight (linear), or just anything else? Obviously, it's just more likely for it to be in some other shape (probably bent, but who knows!). As it isn't linear, it is going to have to be polar (as somewhere there are going to be more electrons etc.). You don't really need to know why it's polar, just that it is

[jakesilove]

Oh I see. Thanks! And what do you mean that only one equation will work? If this was in a long answer question how would you know which one to use?
Actually I believe there was actually a titration question in the HSC in the past that had something similar to this and due to the production of CO2 the titration had 2 equivalence points...Though I think the HSC answer didn't require you to know that lol

All I'm saying is that this particular question wouldn't be asked, because there was more than one way of working it out, and it gives you two different answers. Formulas like Sodium Hydroxide and HCl are much more likely, as there is a clear answer. The HSC won't give you anything vague, or anything that you have a 50% chance of getting right! Don't worry about it

[noonedoesnt]

sorry, uploaded wrong question earlier.

[Cindy2k16]

All I'm saying is that this particular question wouldn't be asked, because there was more than one way of working it out, and it gives you two different answers. Formulas like Sodium Hydroxide and HCl are much more likely, as there is a clear answer. The HSC won't give you anything vague, or anything that you have a 50% chance of getting right! Don't worry about it

Oh ok thank you!

Also some other questions..
1. Is there a simple equation for a radioisotope produced in a cyclotron? The one I have (Iodine 123) is quite complicated so it's hard to memorise and I was wondering if there were any more basic ones?

2. Do we need to know how our chosen radioisotopes (medical, industrial) are produced?

TIA

[jakesilove]

sorry, uploaded wrong question earlier.

We know that



After realising it's a 1:1 reaction, and noting that the moles of each substance must be the same. Therefore




Therefore, in 100mL, there would be



If 1 gram is that many moles, then




Is that the answer? I'm seriously tired and I may have made a calculation error, but that's the method

[jakesilove]

Oh ok thank you!

Also some other questions..
1. Is there a simple equation for a radioisotope produced in a cyclotron? The one I have (Iodine 123) is quite complicated so it's hard to memorise and I was wondering if there were any more basic ones?

2. Do we need to know how our chosen radioisotopes (medical, industrial) are produced?

TIA

I definitely didn't have a cyclotron reaction up my sleeve when I went into the HSC! That's the sort of thing I would only try to learn if you've done absolutely everything else. As for the production of your radioisotope, maybe have a general idea (ie. cyclotron or, more likely, small-scale nuclear reactor and nuclear decay) so you can write half a sentence on it to sound smart, but you really don't need anything in depth.