Chemistry Marathon (HSC) (2 Viewers)

[someth1ng]

Hey guys I just had a quick question (sorry deswa lol)

What makes ozone more reactive that oxygen? Is it because the co-ordinate covalent bond is weak? If so, what makes it weaker than an ordinary covalent bond?
And what makes ozone slightly polar? It's a bent molecule but its net dipole is 0.

1. Ozone is more reactive than oxygen because it has one double bond and one single bond. The single bond is easily broken and hence, ozone is more reactive than oxygen. The coordinate covalent bond is actually the same strength as a normal covalent bond.
2. Ozone is slightly polar because it has a bent structure, also, the distribution of electrons between the structure is uneven making dipoles and hence, polarity (draw Lewis dot diagram).

 

[Sanjeet]

1. Ozone is more reactive than oxygen because it has one double bond and one single bond. The single bond is easily broken and hence, ozone is more reactive than oxygen. The coordinate covalent bond is actually the same strength as a normal covalent bond.
2. Ozone is slightly polar because it has a bent structure, also, the distribution of electrons between the structure is uneven making dipoles and hence, polarity (draw Lewis dot diagram).

Thanks for the reply, is this the extent of the detail we have to know for a band 6 response?

 

[deswa1]

Thanks for the reply, is this the extent of the detail we have to know for a band 6 response?

Yeah you should know that much imo for B6 defs

 

[Sanjeet]

Yeah you should know that much imo for B6 defs

Yea I was just wondering if its bent shape is enough to conclude that it's polar, because the net dipole is 0.

 

[crazy_paki123]

Ozone molecules are definitely polar

 

[Kimyia]

Quick question: with neutralisation reactions, can you say sodium hydrogen carbonate is useful because its amphiprotic but also because when neutralising an acid, it evolves carbon dioxide so you can tell when the reaction is complete as it will stop evolving carbon dioxide bubbles?

 

[someth1ng]

Quick question: with neutralisation reactions, can you say sodium hydrogen carbonate is useful because its amphiprotic but also because when neutralising an acid, it evolves carbon dioxide so you can tell when the reaction is complete as it will stop evolving carbon dioxide bubbles?

Yes, you can say the CO2 halting from production would be an indication of a complete reaction. You should elaborate on the fact that it's amphiprotic and also say that it can neutralise with both acids and bases. As well as that, say that the products are non-toxic.

 

[TheOptimist]

Yes, you can say the CO2 halting from production would be an indication of a complete reaction. You should elaborate on the fact that it's amphiprotic and also say that it can neutralise with both acids and bases. As well as that, say that the products are non-toxic.

Could you also say that it would be safe to use NaHCO^3 in excess?

 

[someth1ng]

Could you also say that it would be safe to use NaHCO^3 in excess?

Definitely, that's one of the advantages of NaHCO3 since it's non-toxic etc.

 

[Kimyia]

Haha thanks! Yeah, I knew the other benefits of NaHCO3, I was just wondering if the carbon dioxide part was correct

 

[Rawf]

Do we always have to do a line of best fit? and will we lose marks if we just connect all the points?
And do we have to write the state symbols if we're doing structural formulas?

 

[someth1ng]

Do we always have to do a line of best fit? and will we lose marks if we just connect all the points?
And do we have to write the state symbols if we're doing structural formulas?

1. You should always do a line/curve of best fit but I believe you will not lose marks unless they specifically asked for it.
2. I don't think it is required to include states but it can't hurt to include them and so, I would recommend always including states.

 

[Rawf]

1. You should always do a line/curve of best fit but I believe you will not lose marks unless they specifically asked for it.
2. I don't think it is required to include states but it can't hurt to include them and so, I would recommend always including states.

Ahh okay in one of my internals i did curve of best fit and i lost a mark though. I saw in successone that there was a graph with line of best fit, and it only had like 2 points on the line and 3-4 pretty off lolol. but it was for AAS though, should we be using a line of best fit for AAS curves?

 

[deswa1]

For every graph I'm pretty sure you need either a line or curve of best fit -> connecting the dots is definitely WRONG. You need to do your line so you have equal number of dots on both sides etc.

For states, I think they pick one or two questions in the whole paper and mark just those on states (same with sig figs) BUT you don't know which ones they'll pick so do states for everything imo

 

[Rawf]

For every graph I'm pretty sure you need either a line or curve of best fit -> connecting the dots is definitely WRONG. You need to do your line so you have equal number of dots on both sides etc.

For states, I think they pick one or two questions in the whole paper and mark just those on states (same with sig figs) BUT you don't know which ones they'll pick so do states for everything imo

I'm pretty confused about sigfigs. Like, I know how to see how many sig figs is in each number, and I've read somewhere on here that we use the number of sigfigs which is the smallest in the question.
However, when I was doing my successone stuff, I'm continually getting them wrong.
ie (just made this one up) 50mL of bla was used, 23.4g salt was weighed, 13.4mL added --> I assume they want it in 2 sig fig because its '50mL' but the answer would have 3 sig fig
for another question, they had all the numbers in 5sig fig like 234.95, 183.73, 103.85 so I assume that they want the ans in 5 sig fig but no -__- it's like in 2 sig fig or something (its a decimal like 0.40)
Lastly, for a pH question, they stated the pH of something was like 5, and then you add water and then you figure out the final pH, the answer was like 6.511 but from the question '5' is 1 sig fig, so I rounded it to 7, and the answer says 6.5.
Will I lose a mark in the exam if I round it to a sig fig (which is rather small.. like 1 or 2) and the marks are not allocated to that? ie. the answer is 3948.83 and I write that down first, and then i round to 2 sig figs --> 3900?

 

[madharris]

I'm pretty confused about sigfigs. Like, I know how to see how many sig figs is in each number, and I've read somewhere on here that we use the number of sigfigs which is the smallest in the question.
However, when I was doing my successone stuff, I'm continually getting them wrong.
ie (just made this one up) 50mL of bla was used, 23.4g salt was weighed, 13.4mL added --> I assume they want it in 2 sig fig because its '50mL' but the answer would have 3 sig fig
for another question, they had all the numbers in 5sig fig like 234.95, 183.73, 103.85 so I assume that they want the ans in 5 sig fig but no -__- it's like in 2 sig fig or something (its a decimal like 0.40)
Lastly, for a pH question, they stated the pH of something was like 5, and then you add water and then you figure out the final pH, the answer was like 6.511 but from the question '5' is 1 sig fig, so I rounded it to 7, and the answer says 6.5.
Will I lose a mark in the exam if I round it to a sig fig (which is rather small.. like 1 or 2) and the marks are not allocated to that? ie. the answer is 3948.83 and I write that down first, and then i round to 2 sig figs --> 3900?

It's definitely the lowest number of sigfigs, i've noticed that successone sometimes gets it wrong.
I don't think usually the pH counts as a sigfig, but I could be wrong.
If there's no marks allocated for sigfigs then you will usually get a mark.

Question of my own: So I noticed in some papers that the AAS graph is a straight line and noticed in some others that the AAS graph is a curved line even if the dots indicate that it would most likely be straight. How do you know when it is a straight line graph and when it is a curved one.
e.g. question 25 in the 2006 paper http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2006exams/pdf_doc/chemistry_06.pdf
is a curved line even though when you draw it out, you would think it's a straight line. Should I always make it a curved line?

Sorry i realised i didn't make much sense, but i'll try explain it again if you want

 

[Rawf]

It's definitely the lowest number of sigfigs, i've noticed that successone sometimes gets it wrong.
I don't think usually the pH counts as a sigfig, but I could be wrong.
If there's no marks allocated for sigfigs then you will usually get a mark.

Question of my own: So I noticed in some papers that the AAS graph is a straight line and noticed in some others that the AAS graph is a curved line even if the dots indicate that it would most likely be straight. How do you know when it is a straight line graph and when it is a curved one.
e.g. question 25 in the 2006 paper http://www.boardofstudies.nsw.edu.au/hsc_exams/hsc2006exams/pdf_doc/chemistry_06.pdf
is a curved line even though when you draw it out, you would think it's a straight line. Should I always make it a curved line?

Sorry i realised i didn't make much sense, but i'll try explain it again if you want

So if I figured out an answer and got 2842.49g (wrote this down) and then the next line i wrote 2800g (2sig figs), and there are no marks allocated to sig figs, I wont lose any marks? What happens if there are no marks allocated to sig figs, but using the data in the question it was supposed to be to 3 sig figs?

& This is exactly the question i was referring to before. when you draw it.. its not straight. However, in the successone answers they used line of best fit, when only 2 of the points lie on the line and 4 of them do not. I think for AAS we have to do a straight line maybe? :S i think my tutor said it's meant to be a straight line (if performed correctly).

 

[Riaa]

Hey guys,
Out of curiosity, if I were to answer a radioisotope question with one that we learnt in Physics (Medical Physics), I should not be penalised right? XD Say if I wrote about Technetium 99m instead of the regular Colbat 60.

 

[study-freak]

Hey guys,
Out of curiosity, if I were to answer a radioisotope question with one that we learnt in Physics (Medical Physics), I should not be penalised right? XD Say if I wrote about Technetium 99m instead of the regular Colbat 60.

many people answer radioisotope questions in chem with Tc-99m
Co-60 might have been what you learnt in chem at school, but is certainly not the 'regular' radioisotope to discuss

so you'll be fine

 

[Kimyia]

Hey guys,
Out of curiosity, if I were to answer a radioisotope question with one that we learnt in Physics (Medical Physics), I should not be penalised right? XD Say if I wrote about Technetium 99m instead of the regular Colbat 60.

Yes, your allowed to write about any radioisotope as examples for medical and industrial use. Tc-99m is actually pretty common, I think.