Login

Welcome, Guest. Please login or register.

March 29, 2024, 11:24:12 pm

Author Topic: VCE Chemistry Question Thread  (Read 2313802 times)  Share 

0 Members and 5 Guests are viewing this topic.

eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #90 on: January 12, 2014, 07:42:49 pm »
0
Thanks I understand this concept however in the table it moves from 0.00 to 21.00 to 1.00 to 22.00 to 2.00 in each titration number. Can you account for this difference?

Edward21

  • Victorian
  • Forum Leader
  • ****
  • Posts: 625
  • Don't ask me, all I do is calculate pH.
  • Respect: +27
Re: VCE Chemistry Question Thread
« Reply #91 on: January 12, 2014, 07:47:12 pm »
0
Thanks I understand this concept however in the table it moves from 0.00 to 21.00 to 1.00 to 22.00 to 2.00 in each titration number. Can you account for this difference?
You're reading the table wrong (sorry if that's harsh!) it's the difference between the start and end that gives you the difference, the ACTUAL titre volume. You can't keep on dispensing liquid from a burette, it runs out, you just make note of where it starts and where it ends, and the difference is the titre :) If you look down the bottom the titres are all fairly similar volumes. When you do titrations in class it will make a lot more sense  :D
2012 Biology [44] 2013 Chemistry [50] Italian [38] English [48] Health & HD [45] Methods [34] ATAR: 99.10

2014-2016 Bachelor of Biomedicine - The University of Melbourne


eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #92 on: January 12, 2014, 08:08:07 pm »
0
Ok thanks! Just to clarify, does that mean after titre 1, more standard solution is poured into the burette, and hence the increase in brunette reading number 2?

Edward21

  • Victorian
  • Forum Leader
  • ****
  • Posts: 625
  • Don't ask me, all I do is calculate pH.
  • Respect: +27
Re: VCE Chemistry Question Thread
« Reply #93 on: January 12, 2014, 08:40:00 pm »
0
Ok thanks! Just to clarify, does that mean after titre 1, more standard solution is poured into the burette, and hence the increase in brunette reading number 2?
Probably, I mean if the end titre of #1 doesn't match the starting of #2 then you can assume something's happened :) It's actually strange that it doesn't follow on logically.. in practice exams I've done it has the final reading of one titration matching the starting of the next?? But as I said when you do this in class you'll see what I mean
2012 Biology [44] 2013 Chemistry [50] Italian [38] English [48] Health & HD [45] Methods [34] ATAR: 99.10

2014-2016 Bachelor of Biomedicine - The University of Melbourne


Snorlax

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 371
  • Snore 'n relax
  • Respect: 0
Re: VCE Chemistry Question Thread
« Reply #94 on: January 12, 2014, 08:48:29 pm »
0
Ok thanks! Just to clarify, does that mean after titre 1, more standard solution is poured into the burette, and hence the increase in brunette reading number 2?

The increase in burette reading would have been because it (the solution in the burette) had been dispensed (probably for convenience).

if MORE solution was poured in, that would have resulted in a decrease in burette reading.

« Last Edit: January 12, 2014, 08:58:30 pm by Snorlax »
2014:
ATAR: 99.96

2015:
B.Sc @ UniMelb
Neuroscience Major

2018:
????????

eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #95 on: January 12, 2014, 08:55:45 pm »
+1
Thanks for the explanation snorlax + edward21!

eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #96 on: January 13, 2014, 09:13:33 am »
0
Convert this molar concentration to units of ppm.
0.0036 M Ca(OH)2 solution.

These are my steps:
0.0036mol / 1000 mL
m(Ca(OH)2) = 0.0036 x (40.1+2x17) = 0.26676g

0.26676g / 1000 g = 266.76g / 1,000,000g

Answer: 2.7 x 102 ppm

Textbook answer: 270 ppm

I want to ask why is it to 3 significant figures? Thank you!

brightsky

  • Victorian
  • ATAR Notes Legend
  • *******
  • Posts: 3136
  • Respect: +200
Re: VCE Chemistry Question Thread
« Reply #97 on: January 13, 2014, 09:21:22 am »
0
The textbook is wrong. Your working is perfect except make sure you write 17.0 and not just 17, because all relative atomic masses are given in the data book to 1 decimal place.
2020 - 2021: Master of Public Health, The University of Sydney
2017 - 2020: Doctor of Medicine, The University of Melbourne
2014 - 2016: Bachelor of Biomedicine, The University of Melbourne
2013 ATAR: 99.95

Currently selling copies of the VCE Chinese Exam Revision Book and UMEP Maths Exam Revision Book, and accepting students for Maths Methods and Specialist Maths Tutoring in 2020!

eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #98 on: January 13, 2014, 09:27:29 am »
0
Thanks for clearing it up!

eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #99 on: January 13, 2014, 01:09:58 pm »
0
Assuming complete disassociation occurs, calculate the pH of the following solution at 25o C : 1M HClO4.

pH = -log10(1) = 0

Can an acid ever have a pH of zero?

Thanks!

Edward21

  • Victorian
  • Forum Leader
  • ****
  • Posts: 625
  • Don't ask me, all I do is calculate pH.
  • Respect: +27
Re: VCE Chemistry Question Thread
« Reply #100 on: January 13, 2014, 01:23:20 pm »
+1
Assuming complete disassociation occurs, calculate the pH of the following solution at 25o C : 1M HClO4.

pH = -log10(1) = 0

Can an acid ever have a pH of zero?

Thanks!
Yes! In fact the standard half-cell (look at your electrochemical series, see the equation with 0.00 Eo value) has a pH of 0 too! You can get negative pH and pH over 14, they just generally come between 0-14 :)
2012 Biology [44] 2013 Chemistry [50] Italian [38] English [48] Health & HD [45] Methods [34] ATAR: 99.10

2014-2016 Bachelor of Biomedicine - The University of Melbourne


eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #101 on: January 13, 2014, 01:30:31 pm »
0
That's interesting, thanks!

Edward21

  • Victorian
  • Forum Leader
  • ****
  • Posts: 625
  • Don't ask me, all I do is calculate pH.
  • Respect: +27
Re: VCE Chemistry Question Thread
« Reply #102 on: January 13, 2014, 01:43:48 pm »
0
That's interesting, thanks!
I remember when I got my first pH of -0.30 (2M acid) and 14.7 NaOH haha :P you learn 0-14 is just a loose guide for most solutions.
2012 Biology [44] 2013 Chemistry [50] Italian [38] English [48] Health & HD [45] Methods [34] ATAR: 99.10

2014-2016 Bachelor of Biomedicine - The University of Melbourne


eagles

  • Victorian
  • Trendsetter
  • **
  • Posts: 140
  • Respect: +5
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #103 on: January 13, 2014, 03:18:25 pm »
0
Just as sharp end points = strong acids and bases and
           broad end points = strong acid/weak base or strong base/weak acid;
I was wondering whether weak acid and weak base would also mean a sharp end point?
Thanks!

Stick

  • Victorian
  • ATAR Notes Legend
  • *******
  • Posts: 3774
  • Sticky. :P
  • Respect: +467
Re: VCE Chemistry Question Thread
« Reply #104 on: January 13, 2014, 03:22:10 pm »
0
Unfortunately I think you've gotten yourself a bit confused there. :S Sharp end points occur whenever a strong acid or base is involved - regardless of whether the other reactant is strong or weak. Broad end points only occur when a weak acid reacts with a weak base. Hopefully that's cleared it up for you. :)
2017-2020: Doctor of Medicine - The University of Melbourne
2014-2016: Bachelor of Biomedicine - The University of Melbourne