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March 29, 2024, 03:47:37 pm

Author Topic: VCE Chemistry Question Thread  (Read 2313582 times)  Share 

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hobbitle

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Re: VCE Chemistry Question Thread
« Reply #570 on: April 11, 2014, 12:08:21 pm »
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Guys I'm doing uni Chem (but only fundamentals), can I ask a question here?

I'm really confused about the 'difference' between oxidation numbers and ionic charges. 
It's clear to me what ionic charges are for standalone ions e.g. Cl-, K+, Ca2+ etc.
Now we have just learned oxidation numbers and their 'rules' which I understand is not the same as the ionic charge - fine.
BUT what seems to happen is that when figuring out the oxidation numbers for individual elements in a compound, sometimes they use the oxidation number 'rules' and sometimes they use the ionic charges.  Like my lecturer today said, for some compound that contained Cl, "The Chlorine has an oxidation number of -1 because it does in it's ionic state." but then thats not the case for other elements. 
I'm REALLY confused about what to use when here, can anyone help?

Here's an example question that I found an answer to online.
Q: What is the oxidation number of iron in K4Fe(CN)6?
Well from the 'rules' we know that Group I elements will carry +1, so the K4 is +4.  That means the net charge of the Fe(CN)6 needs to be -4.
But then the answer goes on to say "CN has a -1 charge. It just does. Hence, CN is contributing -6. "

I know that the polyatomic ion CN has an ionic charge of -1 (CN-) but this just doesn't make sense to me, all of a sudden we are using the ionic charge for the polyatomic ion instead of the oxidation number?
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Rishi97

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Re: VCE Chemistry Question Thread
« Reply #571 on: April 11, 2014, 02:30:54 pm »
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Polyethenes are organic molecules that contain more than one carbon-to-carbon double bond. A particular polyene undergoes an addition reaction with bromine. The empirical formula of the product is C3H5Br2. The molecular formula of the polyene is likely to be:
a) C3H4
b) C3H5
c) C6H8
d) C6H10

I have no idea where to begin ???
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nhmn0301

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Re: VCE Chemistry Question Thread
« Reply #572 on: April 11, 2014, 05:00:05 pm »
+1
Polyethenes are organic molecules that contain more than one carbon-to-carbon double bond. A particular polyene undergoes an addition reaction with bromine. The empirical formula of the product is C3H5Br2. The molecular formula of the polyene is likely to be:
a) C3H4
b) C3H5
c) C6H8
d) C6H10

I have no idea where to begin ???
The answer is D.
Now consider why we eliminate other solutions.
A and B, wrong since we can't see any double bonds there. C is still wrong eve though there is 3 double bonds, when C6H8 react with Br2, our product should be C6H8Br6 I.e C3H4B3.
So the answer is D, use the same method that we reason in answer C to prove that's it's true.
Hope this helps!
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lzxnl

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Re: VCE Chemistry Question Thread
« Reply #573 on: April 11, 2014, 07:09:21 pm »
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Guys I'm doing uni Chem (but only fundamentals), can I ask a question here? Sure! Especially as your question may be a concern to other VCE chemistry students

I'm really confused about the 'difference' between oxidation numbers and ionic charges. 
It's clear to me what ionic charges are for standalone ions e.g. Cl-, K+, Ca2+ etc.
Now we have just learned oxidation numbers and their 'rules' which I understand is not the same as the ionic charge - fine.
BUT what seems to happen is that when figuring out the oxidation numbers for individual elements in a compound, sometimes they use the oxidation number 'rules' and sometimes they use the ionic charges.  Like my lecturer today said, for some compound that contained Cl, "The Chlorine has an oxidation number of -1 because it does in it's ionic state." but then thats not the case for other elements. 
I'm REALLY confused about what to use when here, can anyone help?

Here's an example question that I found an answer to online.
Q: What is the oxidation number of iron in K4Fe(CN)6?
Well from the 'rules' we know that Group I elements will carry +1, so the K4 is +4.  That means the net charge of the Fe(CN)6 needs to be -4.
But then the answer goes on to say "CN has a -1 charge. It just does. Hence, CN is contributing -6. "

I know that the polyatomic ion CN has an ionic charge of -1 (CN-) but this just doesn't make sense to me, all of a sudden we are using the ionic charge for the polyatomic ion instead of the oxidation number?

I've decided to make a separate post in the VCE Chemistry forum about this question. Look for it there (:
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Rishi97

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Re: VCE Chemistry Question Thread
« Reply #574 on: April 12, 2014, 01:46:19 pm »
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Why is the following statement false ? :

Propene undergoes a polymerisation reaction expelling water in the process
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Yacoubb

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Re: VCE Chemistry Question Thread
« Reply #575 on: April 12, 2014, 01:52:44 pm »
+1
Why is the following statement false ? :

Propene undergoes a polymerisation reaction expelling water in the process

Because in polymerisation of propene monomers, all that is occurring is that the double bond breaks to then join the monomers together. Water is not eliminated because there is no way for water to form (there is no hydroxyl, carboxyl, etc groups that react to form water). Thus propene polymerisation is not a condensation reaction.

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Re: VCE Chemistry Question Thread
« Reply #576 on: April 12, 2014, 01:59:14 pm »
+1
Why is the following statement false ? :

Propene undergoes a polymerisation reaction expelling water in the process


Addition polymerisation (eg. polymerisation of alkenes) doesn't liberate water, unlike condensation polymerisation
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Re: VCE Chemistry Question Thread
« Reply #577 on: April 12, 2014, 04:48:29 pm »
+1
Hey guys, please clarify this for me. Thanks

Primary structure of DNA -  Is simply a straight chain of bases covalently bonded to deoxyribose molecules which are linked together by phosphate groups.
Secondary structure of DNA - When two base pairs go through a hydrogen bond with each other.
Tertiary structure of DNA - ?????????????????????????????????????????

Yacoubb

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Re: VCE Chemistry Question Thread
« Reply #578 on: April 12, 2014, 05:05:59 pm »
+1
Hey guys, please clarify this for me. Thanks

Primary structure of DNA -  Is simply a straight chain of bases covalently bonded to deoxyribose molecules which are linked together by phosphate groups.
Secondary structure of DNA - When two base pairs go through a hydrogen bond with each other.
Tertiary structure of DNA - ?????????????????????????????????????????

• Primary structure of DNA: the specific sequence of nucleotide bases of a polynucleotide strand. A nucleotide base consists of a nitrogenous base (A, T, G or C), linked covalently to a phosphate group and a deoxyribose (pentose sugar) part.

• Secondary structure of DNA: this refers to how two anti-parallel polynucleotide strands are linked by weak hydrogen bonding.

For VCE Chemistry, you only need to know about primary & secondary structures.

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Re: VCE Chemistry Question Thread
« Reply #579 on: April 12, 2014, 05:19:36 pm »
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You must know about tertiary structures too. It is the overall 3-D structure of the protein due to interactions between Z groups in each of the amino acid residues. Such interactions include hydrogen bonding (eg. between OH groups between serine residues), ionic interactions between COO- and NH3+ groups in side chains and disulfide bridges between cysteine residues.
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Re: VCE Chemistry Question Thread
« Reply #580 on: April 12, 2014, 05:42:24 pm »
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i'm pretty sure the tertiary structure of DNA is the ionic interaction between DNA (the negatively charged phosphate groups) and histone molecules? i think thushan is talking about protein tertiary structure.
« Last Edit: April 12, 2014, 05:59:38 pm by drake »
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Blondie21

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Re: VCE Chemistry Question Thread
« Reply #581 on: April 12, 2014, 05:49:45 pm »
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i'm pretty sure the tertiary structure of DNA is the ionic interaction between DNA with histone molecules? i think thushan is talking about protein tertiary structure.

is that what the point in the study design: "the role of teritary structures of proteins in enzyme action" is referring to?

Also, do we need to know 'how DNA control biochmeical processes' and 'forensic applications'? I can't find it on the study design 
« Last Edit: April 12, 2014, 05:56:31 pm by Blondie21 »
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vox nihili

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Re: VCE Chemistry Question Thread
« Reply #582 on: April 12, 2014, 05:58:23 pm »
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i'm pretty sure the tertiary structure of DNA is the ionic interaction between DNA with histone molecules? i think thushan is talking about protein tertiary structure.
is that what the point in the study design: "the role of teritary structures of proteins in enzyme action" is referring to?

Also, do we need to know 'how DNA control biochmeical processes' and 'forensic applications'? I can't find it on the study design 

Primary: sequence
Secondary: base pairing
Tertiary: helix



I would highly doubt that you do need to know that, Blondie21
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Re: VCE Chemistry Question Thread
« Reply #583 on: April 12, 2014, 06:07:52 pm »
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Primary: sequence
Secondary: base pairing
Tertiary: helix



I would highly doubt that you do need to know that, Blondie21

Okay phew. Thanks :)))



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Yacoubb

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Re: VCE Chemistry Question Thread
« Reply #584 on: April 12, 2014, 07:48:36 pm »
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You must know about tertiary structures too. It is the overall 3-D structure of the protein due to interactions between Z groups in each of the amino acid residues. Such interactions include hydrogen bonding (eg. between OH groups between serine residues), ionic interactions between COO- and NH3+ groups in side chains and disulfide bridges between cysteine residues.

Yeah thushan DNA was being referred to, not proteins :)