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Joseph41

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QCE Chemistry Questions Thread
« on: January 30, 2019, 03:36:09 pm »
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QCE CHEMISTRY Q&A THREAD

What is this thread for?
If you have general questions about the QCE Chemistry course (both Units 1&2 and 3&4) or how to improve in certain areas, this is the place to ask! 👌


Who can/will answer questions?
Everyone is welcome to contribute; even if you're unsure of yourself, providing different perspectives is incredibly valuable.

Please don't be dissuaded by the fact that you haven't finished Year 12, or didn't score as highly as others, or your advice contradicts something else you've seen on this thread, or whatever; none of this disqualifies you from helping others. And if you're worried you do have some sort of misconception, put it out there and someone else can clarify and modify your understanding! 

There'll be a whole bunch of other high-scoring students with their own wealths of wisdom to share with you, so you may even get multiple answers from different people offering their insights - very cool.


To ask a question or make a post, you will first need an ATAR Notes account. You probably already have one, but if you don't, it takes about four seconds to sign up - and completely free!

Oxford comma, Garamond, Avett Brothers, Orla Gartland enthusiast.

alphabeta

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Re: QCE Chemistry Questions Thread
« Reply #1 on: December 12, 2019, 01:23:27 pm »
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Hello,

Can someone explain how they would go about naming this molecule according to current IUPAC nomenclature conventions?

Thanks in advance,

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Bri MT

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Re: QCE Chemistry Questions Thread
« Reply #2 on: December 12, 2019, 07:33:45 pm »
+5
I am surprised you have been asked to name a cyclic alkane but nonetheless here's the procedure:
1. Count the number of carbons in the ring, there are 6     cyclohexane is the name of a cyclic alkane with 6 carbons
2. Identify the other things we have going on in the ring.
There are:
- 2 C=C in the ring
- 1 C=O
- 1 C-OH
- 1 C-CH3
Of these, it's the C=O that has highest priority so we count from there picking a direction that reduces the numbers of our other functional groups.

In the end we obtain: 3-hydroxy-4-methylcyclohexa-2,5-dien-1-one

Let me know if any part of this doesn't make sense :)

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Re: QCE Chemistry Questions Thread
« Reply #3 on: December 12, 2019, 08:30:51 pm »
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I am surprised you have been asked to name a cyclic alkane but nonetheless here's the procedure:
1. Count the number of carbons in the ring, there are 6     cyclohexane is the name of a cyclic alkane with 6 carbons
2. Identify the other things we have going on in the ring.
There are:
- 2 C=C in the ring
- 1 C=O
- 1 C-OH
- 1 C-CH3
Of these, it's the C=O that has highest priority so we count from there picking a direction that reduces the numbers of our other functional groups.

In the end we obtain: 3-hydroxy-4-methylcyclohexa-2,5-dien-1-one

Let me know if any part of this doesn't make sense :)

Thanks Bri!

I'm still a little confused about some parts. I wasn't actually aware that there was an ''order of functional groups''. Like how you mentioned the numbering of the Carbons depends on where a functional group is. Is there like an order or priority depending on what type of functional group is there? Also I don't understand why 2,5-dien us there. I'm not quite sure what dien is. And based on the structure, i'm not sure why 6 isn't in the dien part too.

Aside from that, everything makes sense to me.
Thanks heaps Bri! Really appreciate it. :)

Bri MT

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Re: QCE Chemistry Questions Thread
« Reply #4 on: December 12, 2019, 08:42:04 pm »
+3
Thanks Bri!

I'm still a little confused about some parts. I wasn't actually aware that there was an ''order of functional groups''. Like how you mentioned the numbering of the Carbons depends on where a functional group is. Is there like an order or priority depending on what type of functional group is there? Also I don't understand why 2,5-dien us there. I'm not quite sure what dien is. And based on the structure, i'm not sure why 6 isn't in the dien part too.

Aside from that, everything makes sense to me.
Thanks heaps Bri! Really appreciate it. :)

No worries!

Different functional groups have different priority, and this comes into play when you have multiple functional groups to consider. I cannot definitively state whether this is assessable at a QCE level as it's not explicitly part of the syllabus but it is part of the IUPAC naming system.

dien is indicating that there are 2 double bonds - one connecting the 2nd carbon to the 3rd carbon & one connecting the 5th carbon to the 6th carbon. Remember that you go for low numbers whenever you have a choice.

Hope this clarifies things!

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Re: QCE Chemistry Questions Thread
« Reply #5 on: December 12, 2019, 09:41:02 pm »
+1
No worries!

Different functional groups have different priority, and this comes into play when you have multiple functional groups to consider. I cannot definitively state whether this is assessable at a QCE level as it's not explicitly part of the syllabus but it is part of the IUPAC naming system.

dien is indicating that there are 2 double bonds - one connecting the 2nd carbon to the 3rd carbon & one connecting the 5th carbon to the 6th carbon. Remember that you go for low numbers whenever you have a choice.

Hope this clarifies things!

Thanks Bri! Can you tell me the functional groups from highest priority to lowest?  Makes much more sense now! :)

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Re: QCE Chemistry Questions Thread
« Reply #6 on: December 12, 2019, 09:54:02 pm »
+3
Thanks Bri! Can you tell me the functional groups from highest priority to lowest?  Makes much more sense now! :)

You're absolutely welcome!

Here they are:
Caboxyl  (highest)
ester
amide
nitrile
aldehyde
ketone
hydroxyl
amine
alkene
alkyne
halogen (lowest)

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Re: QCE Chemistry Questions Thread
« Reply #7 on: January 06, 2020, 12:27:54 pm »
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Hey everyone!

I was recently looking at the qce chemistry syllabus (unit 3, topic 2) and I wasn't quite sure what one of the dot points were referring to. The dot point was:

• recognise the limitation associated with standard reduction potentials


Is this referring to the fact that the EMF can only be calculated accurately at standard conditions? If not, could someone please explain what it is referring to?

Thanks! :)

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Re: QCE Chemistry Questions Thread
« Reply #8 on: January 06, 2020, 12:45:53 pm »
+3
Hey everyone!

I was recently looking at the qce chemistry syllabus (unit 3, topic 2) and I wasn't quite sure what one of the dot points were referring to. The dot point was:

• recognise the limitation associated with standard reduction potentials


Is this referring to the fact that the EMF can only be calculated accurately at standard conditions? If not, could someone please explain what it is referring to?

Thanks! :)

This would be referring to standard conditions being met :)

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Re: QCE Chemistry Questions Thread
« Reply #9 on: January 08, 2020, 03:04:45 pm »
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Hello everyone! :)

I'm just checking if I did my titration calculations correctly. So for a titration of hydrochloric acid using a standard solution of sodium carbonate. 2.5 g of sodium carbonate was dissolved in 200 mL water. The equation is:

2HCl + Na2CO3 --> 2NaCl + CO2 + H2O

The attached results were collected. The unknown concentration is HCl.

If I have missed any values, please let me know.

Thanks so much!

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Re: QCE Chemistry Questions Thread
« Reply #10 on: January 08, 2020, 03:50:25 pm »
+1
Hello everyone! :)

I'm just checking if I did my titration calculations correctly. So for a titration of hydrochloric acid using a standard solution of sodium carbonate. 2.5 g of sodium carbonate was dissolved in 200 mL water. The equation is:

2HCl + Na2CO3 --> 2NaCl + CO2 + H2O

The attached results were collected. The unknown concentration is HCl.

If I have missed any values, please let me know.

Thanks so much!


Hey :)

Can you explain how you arrived at your average titre? It seems to be lower than each of your individual titres.

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Re: QCE Chemistry Questions Thread
« Reply #11 on: January 08, 2020, 04:13:46 pm »
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Quote
Hey :)

Can you explain how you arrived at your average titre? It seems to be lower than each of your individual titres.

So, the titre values are 28.6, 28.8, 29, 28 and 28. Adding them up gives 142.4. 142.4 divided by 5 gives 28.48.

Sine

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Re: QCE Chemistry Questions Thread
« Reply #12 on: January 08, 2020, 04:49:42 pm »
+1
So, the titre values are 28.6, 28.8, 29, 28 and 28. Adding them up gives 142.4. 142.4 divided by 5 gives 28.48.
Your average titre calculation is fine.

Whether it is correct or not will depend on the concentration of HCl (which from what I can see you have not calculated yet). So I am not 100% clear on your question.


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Re: QCE Chemistry Questions Thread
« Reply #13 on: January 08, 2020, 05:08:12 pm »
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So, the titre values are 28.6, 28.8, 29, 28 and 28. Adding them up gives 142.4. 142.4 divided by 5 gives 28.48.

Sorry I completely misread your handwriting!

Like Sine, I'm not sure what your question is

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Re: QCE Chemistry Questions Thread
« Reply #14 on: January 08, 2020, 05:33:34 pm »
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Quote
Your average titre calculation is fine.

Whether it is correct or not will depend on the concentration of HCl (which from what I can see you have not calculated yet). So I am not 100% clear on your question.

Quote
Sorry I completely misread your handwriting!

Like Sine, I'm not sure what your question is

Sorry for being so vague - I was in a bit of a rush lol. So, to clear it up, the titration was using the concentration of sodium carbonate to find the concentration of hydrochloric acid. This is how I calculated its concentration:

moles of sodium carbonate = m/M = 2.5/105.99 = 0.023587 mol
moles of HCl = 2 times 0.023587 (as per molar ratio in equation)
                      = 0.047174 mol

The concentration of HCl = moles/volume = 0.047174/0.02848 = 1.656 M

So, my question is: is what I did right?

Thank you! :)