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March 28, 2024, 11:48:27 pm

Author Topic: VCE Chemistry Free Trial Exam (2017) - written by me!  (Read 32023 times)  Share 

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manishmao

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #30 on: November 08, 2017, 08:47:05 pm »
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Thanks for the response, Just another question about the glycogen ether linkage question. How do you connect 2900 glucose units with only 2.33*10^4 linkages. I got confused doing it since I assumed there would be 28999 peptide linkages. Is it because the molecule of glycogen is made up of multiple polysaccharide chains interwoven and held together by hydrogen bonds / dispersion forces? I thought glycogen was a single circular outward branching polysaccharide in which every glucose molecule is connected (Like this image) https://www.google.com.au/imgres?imgurl=https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/Glycogen_structure.svg/1200px-Glycogen_structure.svg.png&imgrefurl=https://en.wikipedia.org/wiki/Glycogen&h=1187&w=1200&tbnid=B_WXpV1_c6m_hM:&tbnh=186&tbnw=188&usg=__W4-agyGP2HSH3H4TGFb-Hq4ni2A=&vet=10ahUKEwiJmtW42K7XAhXGKJQKHTECDtoQ_B0ImwEwEw..i&docid=vJnmhV5rCcUMsM&itg=1&sa=X&ved=0ahUKEwiJmtW42K7XAhXGKJQKHTECDtoQ_B0ImwEwEw)

Would multiple glycogen polysaccharide chains count as a single glycogen molecule?Just making sure since there are many VCAA questions where they give you the molar mass of a polysaccharide chain and ask you to find how many units of glucose / how many ether linkages etc. Thanks again and sorry for long post; I'm really engaging with this exam.

Phenomenol

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #31 on: November 08, 2017, 09:50:07 pm »
+1
Thanks for the response, Just another question about the glycogen ether linkage question. How do you connect 2900 glucose units with only 2.33*10^4 linkages. I got confused doing it since I assumed there would be 28999 peptide linkages. Is it because the molecule of glycogen is made up of multiple polysaccharide chains interwoven and held together by hydrogen bonds / dispersion forces? I thought glycogen was a single circular outward branching polysaccharide in which every glucose molecule is connected (Like this image) https://www.google.com.au/imgres?imgurl=https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/Glycogen_structure.svg/1200px-Glycogen_structure.svg.png&imgrefurl=https://en.wikipedia.org/wiki/Glycogen&h=1187&w=1200&tbnid=B_WXpV1_c6m_hM:&tbnh=186&tbnw=188&usg=__W4-agyGP2HSH3H4TGFb-Hq4ni2A=&vet=10ahUKEwiJmtW42K7XAhXGKJQKHTECDtoQ_B0ImwEwEw..i&docid=vJnmhV5rCcUMsM&itg=1&sa=X&ved=0ahUKEwiJmtW42K7XAhXGKJQKHTECDtoQ_B0ImwEwEw)

Would multiple glycogen polysaccharide chains count as a single glycogen molecule?Just making sure since there are many VCAA questions where they give you the molar mass of a polysaccharide chain and ask you to find how many units of glucose / how many ether linkages etc. Thanks again and sorry for long post; I'm really engaging with this exam.

I am happy to help you with your questions!

To be honest, I had not thought about this detail when I chose the numbers for the question. I used this page as a reference for writing the question. But it looks like I have slightly incompatible values - there should in reality be about 13/12 glycosidic linkages per glucose unit (one for every glucose and and a branching link approx. every 12 units apart). I will fix this - thanks again for pointing out another inconsistency!

I believe the entire glycogen structure, including all of its individual chains, would be considered one molecule.
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Free VCE Chemistry Trial Exam (2017)

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Ameliapower

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #32 on: November 10, 2017, 01:45:52 pm »
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Hi there! I'm having trouble accessing the file. Would someone be able to send me the link? or post it?

Joseph41

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #33 on: November 10, 2017, 01:50:11 pm »
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Hi there! I'm having trouble accessing the file. Would someone be able to send me the link? or post it?

The exam is attached to the first post of this thread. You'll only be able to download it when logged in to your ATAR Notes account. Are you still having issues with it? :)

Oxford comma, Garamond, Avett Brothers, Orla Gartland enthusiast.

Ameliapower

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #34 on: November 11, 2017, 06:32:56 am »
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All good, I didn’t realise I had to log in to view it, that’s all! What an awesome exam, thank you so much for sharing it with us! 😊

skrrrt

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #35 on: November 11, 2017, 02:49:10 pm »
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Hey guys, can someone explain to me why the answer to question 1 isn't D? I thought changing the concentration doesn't change the equilibrium constant

Phenomenol

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #36 on: November 11, 2017, 03:16:14 pm »
+1
All good, I didn’t realise I had to log in to view it, that’s all! What an awesome exam, thank you so much for sharing it with us! 😊

I'm glad you liked it!

Hey guys, can someone explain to me why the answer to question 1 isn't D? I thought changing the concentration doesn't change the equilibrium constant

Did you mean to say why the answer isn't B?

While it is true that the equilibrium constant does not change, it does not directly explain why there is no equilibrium shift after time t. After all, there are many examples of when the Kc value does not change but there will be a shift towards reactants or products. This shift arises when the reaction quotient differs from Kc at some point in time.
« Last Edit: November 11, 2017, 03:18:33 pm by Phenomenol »
Methods 46, Music Performance 49 (Top Acts), Chemistry 50, English 43, Physics 45, Specialist 48, University Maths 93%

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Stuff I've written:
Free VCE Chemistry Trial Exam (2017)

VCE Chemistry Revision Questions (2017)

PM me if you are looking for a 1/2 or 3/4 VCE Chemistry tutor in 2018. I can also do other subjects including Methods, Specialist and Physics depending on availability.

wij0020

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #37 on: November 11, 2017, 03:43:24 pm »
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Hi there! Thank you for writing this Phenomenol!! :) :) :) Could someone please explain Q18 of the MC questions? Thank you.

Miriam443

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #38 on: November 11, 2017, 04:13:41 pm »
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This is a great exam thank you
But question 6 multiple choice the definition of a condensation reaction is that water introduced but this is not shown in the reaction so doesn't this technically mean it is not a condensation reaction?

vikaschand69

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #39 on: November 11, 2017, 04:31:43 pm »
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matildalwhite

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #40 on: November 11, 2017, 04:44:38 pm »
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Hi I can't seem to find the solutions, could someone please post them again? Thank you!

Maybe_mybest

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #41 on: November 11, 2017, 06:44:34 pm »
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OMG THANKYOU KIND STRANGER!! Just finished it. Took half an hour longer though :( :( :(
I feel so sad  because I don't want to let myself down in this final, very important, exam.
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Maybe_mybest

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #42 on: November 11, 2017, 07:12:56 pm »
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Hello :)
I'm really confused with Question 4b, about the two reactions to convert the triglyceride into biodiesel, using ethanol.
1. isn't biodiesal usually a methyl ester, not using ethanol?
2. isn't it one reaction- transesterfercation- to turn the triglyceride to three biodiesel molecules + glycerol? (heinnamann textbook pg 26)

could you please help?

This is the provided answer:
i. Hydrolysis, then condensation (esterification)
ii. H2O (reagent), H2SO4 or H+ (catalyst), glycerol and linolenic acid (products)
iii. H2SO4 or H+ (catalyst), CH3CH2(CH=CHCH2)3(CH2)6COOCH2CH3
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lasisdabomb

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #43 on: November 11, 2017, 08:01:00 pm »
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Question 1 from multiple choice has confused me. Since the system cannot partially oppose the change in volume, wouldn't diluting the equilibrium solution also decrease the concentration of MgBr2? Not because we have changed the Equilibrium constant, but because we merely increased the volume of the whole solution??

lasisdabomb

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Re: VCE Chemistry Free Trial Exam (2017) - written by me!
« Reply #44 on: November 11, 2017, 08:17:32 pm »
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Quote
"2. isn't it one reaction- transesterfercation- to turn the triglyceride to three biodiesel molecules + glycerol? (heinnamann textbook pg 26)
Quote

You are perfectly correct in saying that this reaction is a transesterification. What's tricky about this question is it requires an understanding about the chemical processes that occur during this type of reaction.

First of all in a transesterification reaction we "transform" one ester into another ester. That being we convert our triglycerides, an ester consisting of a glycerol backbone and 3 fatty acid chains, into a methyl ester, our biodiesel molecule. The only way this conversion can occur is if we break our triglyceride into constituent compounds and then react them with another reagent to form the biodiesel molecule - a two step process

The first step is the initial hydrolysis of the triglyceride. We use a strong base like KOH or NaOH to hydrolyse the triglyceride into glycerol and its fatty acid constituents. Next we add methanol to react with the individual fatty acid molecules. These two compounds will undergo a condensation reaction to form our desired biodiesel molecule.

In summary transesterification is actually a two step process involving both hydrolysis and condensation.
Old Ester ---> Fatty Acid + Glycerol ---> New Ester
 
« Last Edit: November 11, 2017, 08:21:31 pm by lasisdabomb »