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March 29, 2024, 05:45:21 am

Author Topic: VCE Chemistry Question Thread  (Read 2313338 times)  Share 

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Yacoubb

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Re: VCE Chemistry Question Thread
« Reply #630 on: April 15, 2014, 08:05:01 pm »
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I'm not entirely sure. I just want to have a thorough understanding of the concept :)

Very good pickup Katie. Technically, in gas-liquid chromatography, the sample dissolves into the stationary phase, because the stationary phase is a liquid.

http://www.chemguide.co.uk/analysis/chromatography/gas.html

ChemGuide refers to dissolution of the sample in the stationary phase in gas-liquid chromatography.


Thanks thushan :)

katiesaliba

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Re: VCE Chemistry Question Thread
« Reply #631 on: April 16, 2014, 12:58:02 am »
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In TLC, can the partition of a sample be measured in frequency? For example, if I were to compare the adsorption and desorption of a polar amino acid to a less polar amino acid, could I say that the polar amino acid partitions itself less frequently between both phases? Is partition even the right term? I've confused myself  :(

(not entirely sure if my example is right either...)
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rhinwarr

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Re: VCE Chemistry Question Thread
« Reply #632 on: April 16, 2014, 08:28:40 pm »
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In a redox titration using a coloured ion eg. permanganate, would the end point be exactly at the equivalence point?

Yacoubb

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Re: VCE Chemistry Question Thread
« Reply #633 on: April 16, 2014, 08:33:25 pm »
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In TLC, can the partition of a sample be measured in frequency? For example, if I were to compare the adsorption and desorption of a polar amino acid to a less polar amino acid, could I say that the polar amino acid partitions itself less frequently between both phases? Is partition even the right term? I've confused myself  :(

(not entirely sure if my example is right either...)

You can say this :) my teacher has instructed me to use 'partitioning' between the stationary and mobile phase when describing and comparing two components of a sample and how frequently adsorption to and from the stationary phase occurs.

In a redox titration using a coloured ion eg. permanganate, would the end point be exactly at the equivalence point?

Many redox titrations are self-indicating. In theory, the end point is the equivalence point; that is, when the reactants are in their equivalent stoichiometric mole ratios, the indicator (or in this case the solution itself) changes colour simultaneously. In practice, the end point occurs right after the equivalence point.

Blondie21

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Re: VCE Chemistry Question Thread
« Reply #634 on: April 17, 2014, 09:35:53 pm »
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Do we need to know what 1,3 butadiene is for vce chem

Also, which carbon is 'carbon number on' on a benzene molecule? In terms of naming?
« Last Edit: April 17, 2014, 09:38:46 pm by Blondie21 »
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vox nihili

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Re: VCE Chemistry Question Thread
« Reply #635 on: April 17, 2014, 09:53:27 pm »
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Do we need to know what 1,3 butadiene is for vce chem

Also, which carbon is 'carbon number on' on a benzene molecule? In terms of naming?

You should be able to draw 1,3-butadiene from your organic stuff. You don't have to know it per se, but you should be able to read that name and draw the structure.

Arbitrary. If it's attached to anything, normally the biggest group attached will be at C1.
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Blondie21

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Re: VCE Chemistry Question Thread
« Reply #636 on: April 17, 2014, 10:41:17 pm »
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You should be able to draw 1,3-butadiene from your organic stuff. You don't have to know it per se, but you should be able to read that name and draw the structure.

Arbitrary. If it's attached to anything, normally the biggest group attached will be at C1.


what does 'diene' mean?


edit; means that there are two double bonds  :-)))
« Last Edit: April 17, 2014, 10:49:57 pm by Blondie21 »
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vox nihili

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Re: VCE Chemistry Question Thread
« Reply #637 on: April 17, 2014, 10:59:37 pm »
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For some reason it's tilted, I have no idea why. Also apologies for UniMelb pad, it was the only one I had!
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Blondie21

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Re: VCE Chemistry Question Thread
« Reply #638 on: April 17, 2014, 11:05:34 pm »
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ohh makes sense. Thanks!
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hobbitle

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Re: VCE Chemistry Question Thread
« Reply #639 on: April 18, 2014, 09:54:30 am »
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REDUCTION POTENTIALS AND GALVANIC CELL REACTIONS

Can anyone help with this, I'm super confused (this is uni Chem but I think it's the same stuff as VCE 3/4).

Question: Use the standard reduction potential table to predict the outcome of the following reactions in an aqueous solution.  If no reaction occurs, write NR.  If reaction does occur, write a balanced equation.

c) Ag+ + Fe -->

So, here's my logic/thought process. 

From the table:
Ag+ + e- <--> Ag (s)  /  Eo = +0.8 V
Fe2+ + 2e- <--> Fe (s)  / Eo = -0.44 V

So far I see nothing wrong, looks like Ag+ is going to be the oxidant and undergo reduction? 

A bit of swapsies and balancing:

2Ag+ + 2e- <--> 2Ag (s)  /  Eo = +0.8 V
Fe (s) <--> Fe2+ + 2e-   / Eo = -0.44 V

Eocell = Eooxidant - Eoreductant
Eocell = +0.8 - -0.44 = +1.24 V

This is a positive value and this the reaction will be spontaneous and will occur according to the following equation:

2Ag+ + Fe --> Fe2+ + 2Ag

So that's my thought process.... however, apparently there will be no reaction (according to the textbook).  Can anyone tell me what I'm doing wrong?
« Last Edit: April 18, 2014, 10:08:38 am by hobbitle »
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Re: VCE Chemistry Question Thread
« Reply #640 on: April 18, 2014, 11:05:34 am »
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Similar topic, I can't seem to get my head around these half-reactions when they get a bit more complicated.

Question: Write cell diagrams* using the following pairs of half-reactions.  For half-rections in which all the reactants are in solution, assume the use of inert platinum electrodes.  Identify the anode and the cathode.

f)
NO3- (aq) + 4H+ + 3e- <--> NO(g) + 2H2O (l)
MnO4- (aq) + 8H+ (aq) + 5e- <--> Mn2+ + 4H2O (l)

My answer:

anode ---> Pt | NO (g), NO3- || MnO4-, Mn2+ | Pt <-- cathode

Actual answer: 

anode ---> Pt | H+ (aq), NO3- || MnO4-, Mn2+, H+ (aq) | Pt <-- cathode

I guess I'm just generally confused... something I'm missing... like where is the NO (g).... what part are the H+ ions playing here....?


*(Do you do cell diagrams in VCE?  The are written like: anode | electrocyte at anode || electrolyte at cathode | cathode
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Blondie21

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Re: VCE Chemistry Question Thread
« Reply #641 on: April 18, 2014, 04:51:03 pm »
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What is the name for H3C-O-CH3 and can you please explain how you found this answer?
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nhmn0301

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Re: VCE Chemistry Question Thread
« Reply #642 on: April 18, 2014, 05:08:29 pm »
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What is the name for H3C-O-CH3 and can you please explain how you found this answer?
That would be dimethyl ether for the systematic name. Simply because you got 2 methyl groups sticking out from a -O- (which is an ether).
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Blondie21

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Re: VCE Chemistry Question Thread
« Reply #643 on: April 18, 2014, 05:14:52 pm »
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That would be dimethyl ether for the systematic name. Simply because you got 2 methyl groups sticking out from a -O- (which is an ether).

Do you know why it would also be called Methoxymethane?
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thushan

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Re: VCE Chemistry Question Thread
« Reply #644 on: April 18, 2014, 05:15:29 pm »
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What is the name for H3C-O-CH3 and can you please explain how you found this answer?

Methoxymethane. Dimethyl ether is also an acceptable name.

You aren't expected to name ethers in the VCE course.
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