Login

Welcome, Guest. Please login or register.

March 29, 2024, 06:49:04 am

Author Topic: VCE Chemistry Question Thread  (Read 2313373 times)  Share 

0 Members and 5 Guests are viewing this topic.

Lizzy7

  • Victorian
  • Trailblazer
  • *
  • Posts: 35
  • Respect: 0
Re: VCE Chemistry Question Thread
« Reply #405 on: February 27, 2014, 09:50:57 pm »
0
Don't rote learn formulas. Think about where they come from.
Pretend magnesium chloride is a box containing two chloride ions. Then, if you had ten chloride ions, you could put them in five boxes. Hence, the number of magnesium chloride units is half the number of chloride ions.

Mind explosion right now  ;D This was the same principle to my question before, but now your analogy helped me understand it better ! 

^_^ Thank you *cyber high five*


ETTH96

  • Victorian
  • Forum Regular
  • **
  • Posts: 96
  • Respect: 0
Re: VCE Chemistry Question Thread
« Reply #406 on: February 28, 2014, 02:56:45 pm »
0
Hey guys, can someone help me with this question?

All the iron present in a 1.048g sample of a breakfast food was extracted and the total volume of the solution formed was diluted to give a total volume of 100.0 mL. When analysed in the spectrophotometer, an absorbance of 0.23 was obtained. the numerical value for the ion content of this food sample, expressed in mg per 100g of food is...  (A DIAGRAM IS GIVEN, AND AT AN ABSORBANCE OF 0.23, THE CONCENTRATION OF FE(IRON) IS 1.8x10^5 M.

a) 12
b) 1.7
c) 9.6
d) 96

Robert123

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 201
  • Respect: +5
  • School: Kyabram P-12 College
Re: VCE Chemistry Question Thread
« Reply #407 on: February 28, 2014, 06:21:09 pm »
0
Hey guys, can someone help me with this question?

All the iron present in a 1.048g sample of a breakfast food was extracted and the total volume of the solution formed was diluted to give a total volume of 100.0 mL. When analysed in the spectrophotometer, an absorbance of 0.23 was obtained. the numerical value for the ion content of this food sample, expressed in mg per 100g of food is...  (A DIAGRAM IS GIVEN, AND AT AN ABSORBANCE OF 0.23, THE CONCENTRATION OF FE(IRON) IS 1.8x10^5 M.

a) 12
b) 1.7
c) 9.6
d) 96
I don't have a calculator  on me at the moment but the method to solve it will be
n(Fe)=cv
=1.8E-5*0.1=1.8*10^-6 mols
m(fe)=n*M
=1.8*10^-6*55.8 (not 100% sure of iron's molar mass off the top of my head)

From there we know the amount of iron in g within that sample. To calculate how much is in 100g, multiply it by 100/1.048 then convert it into mg ( multiply solution by 10^3)

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 #408 on: March 01, 2014, 05:27:43 pm »
0
How is the gas chromatography instrument calibrated?
Thanks :)
2014: VCE completed
2015-2017: BSc at Melb Uni

DREAM, BELIEVE, ACHIEVE!!!

jgoudie

  • Victorian
  • Trendsetter
  • **
  • Posts: 138
  • Chemisode: an app for studying chemistry
  • Respect: +3
Re: VCE Chemistry Question Thread
« Reply #409 on: March 01, 2014, 08:30:04 pm »
0
In Gas Chromatography you need to run a series of pure standard solutions of varying concentrations.

Pure solutions: you can see the Rt value of the species in question

Varying concentration: You can create a calibration curve and determine the concentration.


How is the gas chromatography instrument calibrated?
Thanks :)
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!

swagsxcboi

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 367
  • Respect: +4
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #410 on: March 01, 2014, 09:13:25 pm »
0
if the average volume of three concordant titres is 22.23333 mL, how do I express it?
22.23mL or 22.20 mL?
2013: Biology [47]

2014 AIMS: English (37)    Methods (37)    Business Management (30)    Chemistry (40)


2015 AIMS:
Applied Science/Physiotherapy Practice at La Trobe

Feel free to PM me about Bio or anything :)

Jason12

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 497
  • Respect: +15
  • School: WCC
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #411 on: March 01, 2014, 11:08:27 pm »
0
a question asked me to work out molarity which is concentration. They then used that value as mol or n to find mass.

how is concentration/molarity the same as n or mol?
2014 ATAR - 88

2015 sem 1 - Bachelor of Business (Accounting/Banking & Finance) - Monash

2015 sem 2 - Present: Bachelor of Commerce (Accounting/Finance), Diploma of Languages (Chinese) - Monash

Limista

  • Victorian
  • Forum Leader
  • ****
  • Posts: 944
  • Respect: +63
  • School Grad Year: 2013
Re: VCE Chemistry Question Thread
« Reply #412 on: March 02, 2014, 04:12:44 am »
0
a question asked me to work out molarity which is concentration. They then used that value as mol or n to find mass.

how is concentration/molarity the same as n or mol?

concentration and no. mole are two different things; they are not the same.

With this question, let's say the concentration value is 5M.

You know that C = n/V
So n = C x V
If C = 5 mol/L, then V = 1L  and n = 5 mol

Applying it to this second formula where   m = n x M
You would substitute n with 5, so m = 5 x M, where M = molar mass
Bachelor of Biomedicine @ The University of Melbourne (II) 2014-2016
Follow me on my blog

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 #413 on: March 02, 2014, 10:02:00 am »
0
if the average volume of three concordant titres is 22.23333 mL, how do I express it?
22.23mL or 22.20 mL?

I don't think it matters too much since you will have to convert it to litres anyway.
2014: VCE completed
2015-2017: BSc at Melb Uni

DREAM, BELIEVE, ACHIEVE!!!

swagsxcboi

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 367
  • Respect: +4
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #414 on: March 02, 2014, 10:10:12 am »
0
I don't think it matters too much since you will have to convert it to litres anyway.
It does matter, that's why I asked
2013: Biology [47]

2014 AIMS: English (37)    Methods (37)    Business Management (30)    Chemistry (40)


2015 AIMS:
Applied Science/Physiotherapy Practice at La Trobe

Feel free to PM me about Bio or anything :)

saba.ay

  • Guest
Re: VCE Chemistry Question Thread
« Reply #415 on: March 02, 2014, 11:08:17 am »
+1
if the average volume of three concordant titres is 22.23333 mL, how do I express it?
22.23mL or 22.20 mL?


Well I'd recommend you use 22.23333 mL in your calculations but if you absolutely have to write it and the number of sig figs is 4, then you'd write 22.23mL . I don't know why you'd round to 22.20 mL ? :/

swagsxcboi

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 367
  • Respect: +4
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #416 on: March 02, 2014, 12:05:44 pm »
0
Well I'd recommend you use 22.23333 mL in your calculations but if you absolutely have to write it and the number of sig figs is 4, then you'd write 22.23mL . I don't know why you'd round to 22.20 mL ? :/
isn't it important to keep your titre to 2 decimal places, rather than 4 sig figs? I mean if it was like 9.00 mL, you wouldn't go to 4 sig figs?
I dunno, my teacher was saying something about rounding your three concordant titres to 0.1 mL - I actually have no idea.
I'll go with 22.23, thanks!
2013: Biology [47]

2014 AIMS: English (37)    Methods (37)    Business Management (30)    Chemistry (40)


2015 AIMS:
Applied Science/Physiotherapy Practice at La Trobe

Feel free to PM me about Bio or anything :)

jgoudie

  • Victorian
  • Trendsetter
  • **
  • Posts: 138
  • Chemisode: an app for studying chemistry
  • Respect: +3
Re: VCE Chemistry Question Thread
« Reply #417 on: March 02, 2014, 12:09:54 pm »
0
The only reason for this i could see is not to go from concentration in to grams, but to go from concentration in mol/L into concentration in g/L.

You are not changing concentration into "mol" into "grams", you are just converting the "mol" in "mol/L" into "grams" in "g/L".

Hope this makes sense.

a question asked me to work out molarity which is concentration. They then used that value as mol or n to find mass.

how is concentration/molarity the same as n or mol?
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!

Jason12

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 497
  • Respect: +15
  • School: WCC
  • School Grad Year: 2014
Re: VCE Chemistry Question Thread
« Reply #418 on: March 02, 2014, 01:14:11 pm »
0
I don't get back titration worded questions. Can anyone tell me the steps required to do the question?

2014 ATAR - 88

2015 sem 1 - Bachelor of Business (Accounting/Banking & Finance) - Monash

2015 sem 2 - Present: Bachelor of Commerce (Accounting/Finance), Diploma of Languages (Chinese) - Monash

RKTR

  • Victorian
  • Forum Leader
  • ****
  • Posts: 613
  • Respect: +17
Re: VCE Chemistry Question Thread
« Reply #419 on: March 02, 2014, 01:32:20 pm »
+1
I don't get back titration worded questions. Can anyone tell me the steps required to do the question?
2HNO3 (aq) +Ca(OH)2 (aq)-->Ca(NO3)2 (aq)+2H2O(l)
n of HNO3=cv=0.050(0.10)=0.0050mol
n of Ca(OH)2=cv=0.060(0.10)=0.0060 mol
from the equation we know that calcium hydroxide is in excess as only 0.0025 of it will react with nitric acid
calcium hydroxide left will be 0.0035 mol
H2SO4(aq)+Ca(OH)2(aq)-->CaSO4(aq)+2H2O(l)
n of sulfuric acid needed = n of calcium hydroxide left=0.0035 mol
v=n/c = 0.0035/0.050 = 0.070L
2015-2017: Bachelor of Biomedicine (Neuroscience)
2018: Doctor of Medicine (Withdrawn)
2019: Bachelor of Commerce (Actuarial Studies?)