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March 29, 2024, 04:11:04 am

Author Topic: VCE Chemistry Question Thread  (Read 2313280 times)  Share 

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Einstein

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Re: VCE Chemistry Question Thread
« Reply #945 on: May 28, 2014, 11:04:26 pm »
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Thanks Izxnl :0 However i didnt grasp all the concepts their, i was wondering if you could dumben (if thats a word) it down a bit haha. :(

lzxnl

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Re: VCE Chemistry Question Thread
« Reply #946 on: May 28, 2014, 11:18:45 pm »
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Which one didn't you get?

For the first one, can you imagine that a ball attracted to the Earth by gravity has more potential energy if you raise it higher and higher above the Earth's surface? A similar thing occurs with the attraction between the positive nucleus and the negative electrons. The further the electron is from the nucleus, the more potential energy it has.

As for the second one, alkali metals only have 1 electron in their valence shell to donate to the sea of delocalised electrons. Consider titanium with four valence electrons to donate. Its metallic bonding is going to be stronger as there are Ti 4+ cations with four times the number of electrons available to bond with as opposed to K+. Also the cation charge for Ti 4+ is bigger. Therefore, the attractions between the cations and the electrons are weaker for alkali metals so they melt at lower temperatures.
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Re: VCE Chemistry Question Thread
« Reply #947 on: May 29, 2014, 01:00:06 pm »
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How do I determine the amount of peptide links in a protein? Or more more specifically, one molecule of insulin?
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TimewaveZero

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Re: VCE Chemistry Question Thread
« Reply #948 on: May 29, 2014, 07:11:47 pm »
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Name of this organic compound?

(CH3)2C(OH)CHClCH2CH3

I don't understand how you can have 2 consecutive CH3 groups in a molecule other than ethane?

EDIT: Nevermind, I realise now that it's 2 CH3 side chains from the following carbon.
« Last Edit: May 29, 2014, 07:17:25 pm by TimewaveZero »
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Re: VCE Chemistry Question Thread
« Reply #949 on: May 29, 2014, 08:26:54 pm »
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If
n(Na2SO4.H2O) = 0.094mol,
does
n(H2O) = 0.094mol
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Re: VCE Chemistry Question Thread
« Reply #950 on: May 29, 2014, 08:38:09 pm »
+1
If
n(Na2SO4.H2O) = 0.094mol,
does
n(H2O) = 0.094mol
That's right.
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Yacoubb

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Re: VCE Chemistry Question Thread
« Reply #951 on: June 01, 2014, 08:59:13 am »
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Could someone please check if my answers to these questions are correct? Thanks :)

1. What are the differences between phenol and alcohol?
Phenol is an aromatic organic compound made up of a benzene ring attached to a hydroxyl group, whereas an alcohol is an organic compound containing a hydroxyl functional group.

2. How can we test a sample to prove that it is a phenol and not alcohol?
By reacting the sample with iron (III) salt. If a dark purple-coloured solution results, the sample contains phenol. However, if no reaction occurs and the colour of the solution does not become purple, the sample is an alcohol.

3a. What type of reaction is the synthesis of aspirin?
Esterification (condensation)

b. What does it mean when the reaction is written with a double arrow? And what is the effect of this on the yield of aspirin?
The double-arrow denotes this reaction as a reversible reaction. Because of this, the water produced as a by-product of this condensation reaction can react with the aspirin produced, hydrolysing the aspirin to produce salicylic acid and ethanoic acid. Hence, the yield of aspirin is quite low and this method of aspirin synthesis is inefficient.

4. What are the two functional groups of aspirin?
- Ester linkage
- Carboxyl group

5a. Phosphoric acid is a catalyst in this reaction. What is a catalyst?
A catalyst is a substance that increases the rate of chemical reactions by lowering the activation energy of that reaction.

b. How might a chemical prove that Phophoric acid acts as a catalyst, rather than as a reactant, in this reaction?
(wasn't too sure about this)
By repeating the experiment numerous times and each time using a different amount of H3PO4, while all other variables are kept constant. The mass of aspirin obtained is then measured. If there is minimal to no variation in the amount of aspirin obtained, this proves that because H3PO4 is a catalyst speeding up the reaction rate and not a reactant, the amount of phosphoric acid added does not affected the amount of aspirin obtained.


Limista

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Re: VCE Chemistry Question Thread
« Reply #952 on: June 01, 2014, 09:40:01 am »
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Yacoubb, you could add something like this for part 5 in your own words:

A catalyst is not consumed in a reaction (it's crucial you mention this). This is why it is not a reactant.

The other two points you mentioned about how a catalyst speeds up a reaction and lowers activation energy by providing an alternative reaction pathway are correct.

And the rest of your answers look fine to me. Your method for checking H3PO4 acting as a catalyst for 5b) is also correct. Just bear in mind that as you increase the amount of H3PO4 that you react with x (where x = reagents), the mass of aspirin you calculate at the end would also increase. This is because H3PO4 will still be present amongst the products at the completion of the reaction, because as a catalyst, it is not consumed in the reaction.  :)
« Last Edit: June 01, 2014, 09:46:00 am by Starfish »
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swagsxcboi

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Re: VCE Chemistry Question Thread
« Reply #953 on: June 01, 2014, 09:43:56 am »
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4. What are the two functional groups of aspirin?
- Ester linkage
- Carboxyl group
not sure where your school stands on this, but my 'teacher' suggests that the benzene ring counts as a functional group.
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Re: VCE Chemistry Question Thread
« Reply #954 on: June 01, 2014, 09:48:16 am »
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not sure where your school stands on this, but my 'teacher' suggests that the benzene ring counts as a functional group.

I don't recall the benzene ring (or aromatic compounds at all, actually!) being discussed to a great extent in the 3/4 course.

But the benzene is a functional group - that's true.
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Yacoubb

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Re: VCE Chemistry Question Thread
« Reply #955 on: June 01, 2014, 09:53:06 am »
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Yacoubb, you could add something like this for part 5 in your own words:

A catalyst is not consumed in a reaction (it's crucial you mention this). This is why it is not a reactant.

The other two points you mentioned about how a catalyst speeds up a reaction and lowers activation energy by providing an alternative reaction pathway are correct.

And the rest of your answers look fine to me. Your method for checking H3PO4 acting as a catalyst for 5b) is also correct. Just bear in mind that as you increase the amount of H3PO4 that you react with x (where x = reagents), the mass of aspirin you calculate at the end would also increase. This is because H3PO4 will still be present amongst the products at the completion of the reaction, because as a catalyst, it is not consumed in the reaction.  :)

Okay thanks for that. So what would be a better way to way to go with describing how H3PO4 is a catalyst and not a reactant? Like how should I word it?

not sure where your school stands on this, but my 'teacher' suggests that the benzene ring counts as a functional group.


I think that benzene is a functional group too, but I think the main ones my teacher was looking for were those two.


Limista

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Re: VCE Chemistry Question Thread
« Reply #956 on: June 01, 2014, 10:04:59 am »
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5a. Phosphoric acid is a catalyst in this reaction. What is a catalyst?
A catalyst is a substance that increases the rate of chemical reactions by lowering the activation energy of that reaction, providing an alternative reaction pathway. It is also not consumed in a chemical reaction.

b. How might a chemical prove that Phophoric acid acts as a catalyst, rather than as a reactant, in this reaction?
(wasn't too sure about this)
By repeating the experiment numerous times and each time using a different amount of H3PO4, while all other variables (such as temperature, pressure, amount of reactant) are kept constant. The mass of aspirin obtained should increase proportionate to increase in amount of H3PO4 added. This proves that H3PO4 is acting as a catalyst, since it is not consumed in the reaction, and is still present in the reaction mixture at the completion of the reaction.

I've added to what you've written above.
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lzxnl

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Re: VCE Chemistry Question Thread
« Reply #957 on: June 01, 2014, 11:02:13 am »
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Could someone please check if my answers to these questions are correct? Thanks :)

1. What are the differences between phenol and alcohol?
Phenol is an aromatic organic compound made up of a benzene ring attached to a hydroxyl group, whereas an alcohol is an organic compound containing a hydroxyl functional group.

2. How can we test a sample to prove that it is a phenol and not alcohol?
By reacting the sample with iron (III) salt. If a dark purple-coloured solution results, the sample contains phenol. However, if no reaction occurs and the colour of the solution does not become purple, the sample is an alcohol.

3a. What type of reaction is the synthesis of aspirin?
Esterification (condensation)

b. What does it mean when the reaction is written with a double arrow? And what is the effect of this on the yield of aspirin?
The double-arrow denotes this reaction as a reversible reaction. Because of this, the water produced as a by-product of this condensation reaction can react with the aspirin produced, hydrolysing the aspirin to produce salicylic acid and ethanoic acid. Hence, the yield of aspirin is quite low and this method of aspirin synthesis is inefficient.

4. What are the two functional groups of aspirin?
- Ester linkage
- Carboxyl group

5a. Phosphoric acid is a catalyst in this reaction. What is a catalyst?
A catalyst is a substance that increases the rate of chemical reactions by lowering the activation energy of that reaction.

b. How might a chemical prove that Phophoric acid acts as a catalyst, rather than as a reactant, in this reaction?
(wasn't too sure about this)
By repeating the experiment numerous times and each time using a different amount of H3PO4, while all other variables are kept constant. The mass of aspirin obtained is then measured. If there is minimal to no variation in the amount of aspirin obtained, this proves that because H3PO4 is a catalyst speeding up the reaction rate and not a reactant, the amount of phosphoric acid added does not affected the amount of aspirin obtained.

I think you also need to show that phosphoric acid actually speeds up the reaction too, although that's easy to prove xP

I've added to what you've written above.

Why should mass of aspirin increase? Assuming you've filtered and purified your product properly, the catalytic H3PO4 shouldn't be in the aspirin.
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Limista

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Re: VCE Chemistry Question Thread
« Reply #958 on: June 01, 2014, 11:25:09 am »
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I think you also need to show that phosphoric acid actually speeds up the reaction too, although that's easy to prove xP

Why should mass of aspirin increase? Assuming you've filtered and purified your product properly, the catalytic H3PO4 shouldn't be in the aspirin.

I didn't assume he would do this - as in filter and purify his product. But yes, once he's done this, then he should still find the same mass of aspirin. But the mass of product would have supposedly increased before purification. That's how he would measure that the increase in mass is due to the additional H3PO4.
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Re: VCE Chemistry Question Thread
« Reply #959 on: June 01, 2014, 11:46:50 am »
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Anyone/school started Unit 4 already?
How is it, compared to Unit 3? More challenging? More interesting?
Starting next week  ;D
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