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August 26, 2019, 10:11:03 am

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Bri MT

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Re: Chemistry Question Thread
« Reply #3645 on: November 04, 2018, 12:05:23 pm »
+1
Hey, so isomers are just the same molecule with a different structure, it's a bit hard to describe without diagrams but for example, both 1-bromo-1-chloropentane and 1-bromo-2-chloropentane are both isomers of that molecule. So, the isomers of C3H6BrCl are:

1-bromo-1-chloropentane
1-bromo-2-chloropentane
2-bromo-2-chloropentane
2-bromo-1-chloropentane

"pent" is for 5 carbons in the chain,  "prop" is for 3

1 bromo 3 chloro

Thankyou for having a go at the question and explaining isomerism :)
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Re: Chemistry Question Thread
« Reply #3646 on: November 04, 2018, 01:42:15 pm »
0
Hey, so isomers are just the same molecule with a different structure, it's a bit hard to describe without diagrams but for example, both 1-bromo-1-chloropentane and 1-bromo-2-chloropentane are both isomers of that molecule. So, the isomers of C3H6BrCl are:

1-bromo-1-chloropentane
1-bromo-2-chloropentane
2-bromo-2-chloropentane
2-bromo-1-chloropentane

Those are the only isomers of C3H6BrCl so the answer is 4.

hey, going back to what @Fergus6748 said, he was actually missing one more isomer. so the correct answer should be

1-bromo-1-chloropropane
1-bromo-2-chloropropane
2-bromo-2-chloropropane
2-bromo-1-chloropropane

as well as 1-bromo-3-chloropropane

therefore there are 5 isomers hence c

I hope this helps

horse9996

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Re: Chemistry Question Thread
« Reply #3647 on: November 04, 2018, 01:45:27 pm »
0
Does anyone have any predictions for tomorrow's paper?
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Re: Chemistry Question Thread
« Reply #3648 on: November 04, 2018, 01:53:39 pm »
+3
For saponification, you know how you add oil, sodium hydroxide and a water/ethanol mixture into a beaker which is heated to make the soap? Why is the ethanol added, what's its purpose?

again, adding on to what @Fergus6748 said, basically the "equation" for saponification is

ESTER + NAOH <----> SODUM CARBOXYLATE + ALKANOL

an example would be an ester being ETHYL METHANOATE

SO IT WOULD BE ETHYL METHANOATE  + NAOH <----> SODUM METHANOATE + ETHANOL

so the use of ethanol, is for making the ester along with an alkaloid acid which on this case is methanol acid. and being. byproduct of the reaction

I hope this makes sense

Fergus6748

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Re: Chemistry Question Thread
« Reply #3649 on: November 04, 2018, 03:47:37 pm »
+1
Does anyone have any predictions for tomorrow's paper?
It's going to be hard?? aha
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horse9996

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Re: Chemistry Question Thread
« Reply #3650 on: November 04, 2018, 04:14:27 pm »
0
It's going to be hard?? aha

Haha yea, based on the other exams so far this year
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InnererSchweinehund

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Re: Chemistry Question Thread
« Reply #3651 on: November 05, 2018, 08:11:15 pm »
0
Hey,
I was wondering if anyone could give advice on the best way to study for a practical exam - specifically a titration exams.
Also does anyone know of any past papers / practice exams I could do for preparation for ^^ and where to access these?? I just want to know what the common questions are sort of thing.
Thanks!!

Bri MT

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Re: Chemistry Question Thread
« Reply #3652 on: November 05, 2018, 11:02:46 pm »
0
Hey,
I was wondering if anyone could give advice on the best way to study for a practical exam - specifically a titration exams.
Also does anyone know of any past papers / practice exams I could do for preparation for ^^ and where to access these?? I just want to know what the common questions are sort of thing.
Thanks!!

I didn't do HSC but here are some things to watch out for:
- what are you rinsing the glassware with and why? What would happen if you didn't rinse correctly?
- what's the difference between the end point and equivalence point?
- why is the indicator suitable for this reaction? What would be the consequence of using an unsuited indicator?
- what would the pH curve look like?
- how did you read a burette and to how many decimal places?
- what are concordant titres and why are they important?
- why is it good to use a white background?
- what are the characteristics of a good standard? 
« Last Edit: November 06, 2018, 07:49:00 am by miniturtle »
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charlottemchenry

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Re: Chemistry Question Thread
« Reply #3653 on: November 05, 2018, 11:11:54 pm »
+1
Hey,
I was wondering if anyone could give advice on the best way to study for a practical exam - specifically a titration exams.
Also does anyone know of any past papers / practice exams I could do for preparation for ^^ and where to access these?? I just want to know what the common questions are sort of thing.
Thanks!!

My class did this for the exam and pretty much exactly what miniturtle said. We had 30 marks of questions at it was made up of those things.

Just know your equations ie like weak strong all that. Know which indicator and how to rinse glassware.

Not sure if your school allowed this but my school did it so like we did it in class and then could go at lunch a week before exam for another practice. So we did it twice before the prac in groups so maybe ask if you could do that.

Just try make your measurements as accurate as possible.

Good luck!
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david.wang28

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Re: Chemistry Question Thread
« Reply #3654 on: November 06, 2018, 12:05:56 pm »
0
Hello,
I'm just here to ask about question 10 b,c and d about my chemistry hw. May I please get a detailed reply ASAP? Thanks! :)
« Last Edit: November 06, 2018, 12:08:09 pm by david.wang28 »
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Fergus6748

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Re: Chemistry Question Thread
« Reply #3655 on: November 06, 2018, 12:21:02 pm »
+4
Hello,
I'm just here to ask about question 10 b,c and d about my chemistry hw. May I please get a detailed reply ASAP? Thanks! :)
Heya, is the new syllabus, I will give it a go!

(10.b) So at point A, Q will increase as the system reaches equilibrium as the equilibrium is shifting to the right, producing more products, and because we know that:

Q = Products/Reactants

Since the concentration of the products is increasing while the concentrations of the reactants is decreasing as the system reaches equilibrium. Thus, you can say that Q is going to increase.

(10.c) So what has happened is that the concentration of lead (Pb) has increased sharply because excess lead has been added to the chamber. From there, the equilibrium is shifting to the right to produce more products to counteract the sharp rise in lead, according to Le Chatelier's Principle. Le Chatelier's Principle states that a system at equilibrium will adjust itself to reduce any change in the system. So in this case, the change is the increase in lead that has been added, thus the system has produced more products (PbNO3) to counteract the change. It then reaches a new equilibrium.

(10.d) that is literally the exact same question as (10.c) so is that a mistake?

Hope this helps!!
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david.wang28

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Re: Chemistry Question Thread
« Reply #3656 on: November 06, 2018, 12:29:44 pm »
0
Yes, d should be ignored, it's a mistake. But thanks for the help Fergus!
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david.wang28

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Re: Chemistry Question Thread
« Reply #3657 on: November 07, 2018, 11:52:06 am »
0
Hello,
I'm here to ask about Question 9, 10 and 11 as shown in the attachment. I've attempted them, but can anyone please give me corrections if need be? Thanks :)
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InnererSchweinehund

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Re: Chemistry Question Thread
« Reply #3658 on: November 07, 2018, 08:39:10 pm »
0
I didn't do HSC but here are some things to watch out for:
- what are you rinsing the glassware with and why? What would happen if you didn't rinse correctly?
- what's the difference between the end point and equivalence point?
- why is the indicator suitable for this reaction? What would be the consequence of using an unsuited indicator?
- what would the pH curve look like?
- how did you read a burette and to how many decimal places?
- what are concordant titres and why are they important?
- why is it good to use a white background?
- what are the characteristics of a good standard?

My class did this for the exam and pretty much exactly what miniturtle said. We had 30 marks of questions at it was made up of those things.

Just know your equations ie like weak strong all that. Know which indicator and how to rinse glassware.

Not sure if your school allowed this but my school did it so like we did it in class and then could go at lunch a week before exam for another practice. So we did it twice before the prac in groups so maybe ask if you could do that.

Just try make your measurements as accurate as possible.

Good luck!

Thanks so much!!

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Re: Chemistry Question Thread
« Reply #3659 on: November 11, 2018, 03:32:19 pm »
+2
Hello everyone! I know there have been a couple of questions already, but just putting this here as a marker for the new syllabus which kicks in for 2019 exams and beyond. Everything before this is still useful, there are a fair few places where the new course overlaps with the old, but do look at posts before this line with a bit of a grain of salt.

Keen to see this thread be just as much of a collaborative resource for the new course as it was for the old :)