Login

Welcome, Guest. Please login or register.

March 28, 2024, 07:20:44 pm

Author Topic: VCE Chemistry Question Thread  (Read 2312957 times)  Share 

0 Members and 1 Guest are viewing this topic.

PB

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 387
  • Hi!
  • Respect: +16
  • School: Class of 2018: Griffith BOHDS II
  • School Grad Year: 2013
Re: VCE Chemistry Question Thread
« Reply #495 on: March 21, 2014, 11:35:32 pm »
+4
lol what the... I think they have used the wrong formula.  c1v1=c2v2   should only be used when you are trying to find the concentration of a solution after is has been diluted with water.   

I am pretty the answers are wrong man :P because what their working out would be finding out is the new concentration of HCl in the mineral water after it has been diluted to 20mls from 12.30mls.   

and mind you, it is not even the molarity of HCl we are after...it is K2CO3.  Pretty sure the solutions are wrong.

P.S. how about some +1's if I have helped you hey? ;)    Help me up to +5 respect on my 300th post!

2013
Physics:50 (Premier's)

ATAR: 99.55

Selling my neat, concise cheatsheet for only $15! Has got extra shortcut formulas which you can get nowhere else, and includes vital watchouts for the exam!

Rishi97

  • Victorian
  • Part of the furniture
  • *****
  • Posts: 1042
  • Respect: +40
  • School: The University of Melbourne
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #496 on: March 22, 2014, 03:06:09 pm »
0
Can someone pls help me with MC q9 in  chem exam 1 2012?
Its naming compounds and I really suck at it :(
2014: VCE completed
2015-2017: BSc at Melb Uni

DREAM, BELIEVE, ACHIEVE!!!

PB

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 387
  • Hi!
  • Respect: +16
  • School: Class of 2018: Griffith BOHDS II
  • School Grad Year: 2013
Re: VCE Chemistry Question Thread
« Reply #497 on: March 22, 2014, 05:57:26 pm »
+4
Ok well, first up - we know that this is an ester due to the COO- group trapped in the middle of the carbon chain.
and how do we name esters? its easy dw.
Lets take a look at how esters are formed first. It is formed from a carboxylic acid joining together with an alcohol.

Looking at the diagram, we can see that what was once the carboxylic acid in the ester has three carbons (CH3CH2COO...) so it would form the SECOND part of the name - propanOATE.

The first part of the ester's name would simply be related to the other carbon chain hanging off on the other side of the ester. In the diagram, we can see that this carbon chain is only 2 carbons long.  Hence the FIRST part of the name would be - ethYL.

Put the two parts together and you get Ethyl Propanoate.

So it goes that the general 'formula' of ester nomenclature is   -   (prefix 1)yl   (prefix 2)oate.

where:
(prefix 1) =  the number of carbons in what was once the alcohol
(prefix 2) =  the number of carbons in what was once the carboxylic acid
« Last Edit: March 22, 2014, 06:04:02 pm by PB »
2013
Physics:50 (Premier's)

ATAR: 99.55

Selling my neat, concise cheatsheet for only $15! Has got extra shortcut formulas which you can get nowhere else, and includes vital watchouts for the exam!

Rishi97

  • Victorian
  • Part of the furniture
  • *****
  • Posts: 1042
  • Respect: +40
  • School: The University of Melbourne
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #498 on: March 22, 2014, 06:38:21 pm »
0
OMG THANK YOU SOOOO MUCH!!!!
U r so good at explaining things. I would give u more than +1 if I could.
Kind request, whoever benefitted from PB's explanation, pls +1
2014: VCE completed
2015-2017: BSc at Melb Uni

DREAM, BELIEVE, ACHIEVE!!!

PB

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 387
  • Hi!
  • Respect: +16
  • School: Class of 2018: Griffith BOHDS II
  • School Grad Year: 2013
Re: VCE Chemistry Question Thread
« Reply #499 on: March 22, 2014, 07:13:00 pm »
+3
Thanks rishi :) really appreciate it!
2013
Physics:50 (Premier's)

ATAR: 99.55

Selling my neat, concise cheatsheet for only $15! Has got extra shortcut formulas which you can get nowhere else, and includes vital watchouts for the exam!

eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #500 on: March 23, 2014, 08:45:50 am »
0
Hi! Please see attached the problem I'm working on.
Should the answer to question b) be component B as it is more strongly absorbed to the stationary phase than component a? Thus it will travel more slowly and move least distance on the paper. Hence the lower RF value.

Thank you!

jgoudie

  • Victorian
  • Trendsetter
  • **
  • Posts: 138
  • Chemisode: an app for studying chemistry
  • Respect: +3
Re: VCE Chemistry Question Thread
« Reply #501 on: March 23, 2014, 11:10:06 am »
+1
The only problem I can see is that the question said "absorbed" instead of "adsorbed".  In chromatography compounds are adsorbed (bonded to the stationary phase) not absorbed (taken into).  Could be a typo, but you do need to be careful not to confuse the two.

Your logic is correct in regards to Rf values though.

Hi! Please see attached the problem I'm working on.
Should the answer to question b) be component B as it is more strongly absorbed to the stationary phase than component a? Thus it will travel more slowly and move least distance on the paper. Hence the lower RF value.

Thank you!
Chemisode: A podcast, iPhone/iPad app for studying VCE chemistry.

Search the appstore: "Chemisode"
http://www.facebook/chemisode34
http://www.facebook/chemisode12
http://jgoudie.podomatic.com/
http://www.youtube.com/mrjasongoudie
Iphone and Ipad apps: 'Chemisode' out in the app store now!

Blondie21

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 489
  • Respect: +13
  • School: Lakeview Senior College
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #502 on: March 23, 2014, 04:44:55 pm »
0
"Write a sequence of reactions that shows the production of ethanoic acid to ethane"

The answers state that

First Cl is used as a catalyst to subtitute H

Then OH is used to substitute the Cl

Then it is oxidised and becomes ethanoic acid


But why? Why is ethane reacted with Cl first? Why can't ethane react with OH first? I'm confused about the whole process. Can someone please explain what has happened? Thanks :)
« Last Edit: March 23, 2014, 04:46:48 pm by Blondie21 »
'15 - '17: The University of Melbourne - Bachelor of Science

PB

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 387
  • Hi!
  • Respect: +16
  • School: Class of 2018: Griffith BOHDS II
  • School Grad Year: 2013
Re: VCE Chemistry Question Thread
« Reply #503 on: March 23, 2014, 04:58:50 pm »
+1
lol, this question has been asked soooo many times, even in the years before you XD
In the end everyone just takes it as a fact and moves on because the actual mechanics of it is way out of the course. :P

Simply put, it is easier to substitute a Cl with OH than it is to substitute a H with OH (you also get higher yield of Ethanol this way). VCAA is NEVER going to test you on why that is - just that it is that way. 

One more thing, Chlorine is NOT the catalyst as it takes part in the reaction.  UV light is the catalayst.

Hope that helps :P
« Last Edit: March 23, 2014, 05:15:44 pm by PB »
2013
Physics:50 (Premier's)

ATAR: 99.55

Selling my neat, concise cheatsheet for only $15! Has got extra shortcut formulas which you can get nowhere else, and includes vital watchouts for the exam!

Blondie21

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 489
  • Respect: +13
  • School: Lakeview Senior College
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #504 on: March 23, 2014, 05:13:22 pm »
0
lol, this question has been asked soooo many times, even in the years before you XD
In the end everyone just takes it as a fact and moves on because the actual mechanics of it is way out of the course. :P

Simply put, it is easier to substitute a Cl than with OH than it is to substitute a H with OH (you also get higher yield of Ethanol this way). VCAA is NEVER going to test you on why that is - just that it is that way. 

One more thing, Chlorine is NOT the catalyst as it takes part in the reaction.  UV light is the catalayst.

Hope that helps :P

ohh okay thanks :)

So do alkanes always have to react with Cl? My friend said that they can react with any of the halogens?
'15 - '17: The University of Melbourne - Bachelor of Science

PB

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 387
  • Hi!
  • Respect: +16
  • School: Class of 2018: Griffith BOHDS II
  • School Grad Year: 2013
Re: VCE Chemistry Question Thread
« Reply #505 on: March 23, 2014, 05:16:44 pm »
+1
Yeah for sure, you could do it with Bromine as well.  Just as long as the halogen is electronegative enough :)
2013
Physics:50 (Premier's)

ATAR: 99.55

Selling my neat, concise cheatsheet for only $15! Has got extra shortcut formulas which you can get nowhere else, and includes vital watchouts for the exam!

thushan

  • ATAR Notes Lecturer
  • Honorary Moderator
  • ATAR Notes Legend
  • *******
  • Posts: 4959
  • Respect: +626
Re: VCE Chemistry Question Thread
« Reply #506 on: March 23, 2014, 05:22:04 pm »
+1
Yeah for sure, you could do it with Bromine as well.  Just as long as the halogen is electronegative enough :)

Iodine works too. Fluorine doesn't, though. If you mix methane and fluorine, fluorine just rips all the H out and you get C and HF.
Managing Director  and Senior Content Developer - Decode Publishing (2020+)
http://www.decodeguides.com.au

Basic Physician Trainee - Monash Health (2019-)
Medical Intern - Alfred Hospital (2018)
MBBS (Hons.) - Monash Uni
BMedSci (Hons.) - Monash Uni

Former ATARNotes Lecturer for Chemistry, Biology

PB

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 387
  • Hi!
  • Respect: +16
  • School: Class of 2018: Griffith BOHDS II
  • School Grad Year: 2013
Re: VCE Chemistry Question Thread
« Reply #507 on: March 23, 2014, 05:24:46 pm »
+2
Iodine works too. Fluorine doesn't, though. If you mix methane and fluorine, fluorine just rips all the H out and you get C and HF.

What he said ^
2013
Physics:50 (Premier's)

ATAR: 99.55

Selling my neat, concise cheatsheet for only $15! Has got extra shortcut formulas which you can get nowhere else, and includes vital watchouts for the exam!

Jawnle

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 210
  • Respect: +2
Re: VCE Chemistry Question Thread
« Reply #508 on: March 23, 2014, 05:49:37 pm »
0
Chem Klub or Khem Club?

lzxnl

  • Victorian
  • ATAR Notes Legend
  • *******
  • Posts: 3432
  • Respect: +215
Re: VCE Chemistry Question Thread
« Reply #509 on: March 23, 2014, 06:01:58 pm »
0
Iodine works too. Fluorine doesn't, though. If you mix methane and fluorine, fluorine just rips all the H out and you get C and HF.

What about excess fluorine? :D
2012
Mathematical Methods (50) Chinese SL (45~52)

2013
English Language (50) Chemistry (50) Specialist Mathematics (49~54.9) Physics (49) UMEP Physics (96%) ATAR 99.95

2014-2016: University of Melbourne, Bachelor of Science, Diploma in Mathematical Sciences (Applied Maths)

2017-2018: Master of Science (Applied Mathematics)

2019-2024: PhD, MIT (Applied Mathematics)

Accepting students for VCE tutoring in Maths Methods, Specialist Maths and Physics! (and university maths/physics too) PM for more details