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March 28, 2024, 09:38:15 pm

Author Topic: VCE Chemistry Question Thread  (Read 2313041 times)  Share 

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antigony

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Re: VCE Chemistry Question Thread
« Reply #8070 on: July 22, 2019, 07:14:47 pm »
+1
Could someone please check this section of my organic notes and point out any inaccuracies? Thank you!

--------

saturated: all single bonds between carbon atoms
unsaturated: has double or triple bonds between carbon atoms

A homologous series is a group of organic chemical compounds that have similar structures which differ only by the number of CH2 units in the main carbon chain. They have similar chemical properties but different physical properties.

The longer the carbon chain:
   • the higher the boiling point
   • the higher the flashpoint (how soon a liquid becomes volatile)
   • the higher the volatility
   • the higher the viscosity
   • the lower the solubility

These are because the longer the chain, the higher the chance for an uneven distribution of electrons, increasing the strength of bonding via dipole-dipole forces.
If you were given a list of hydrocarbons and asked which was most likely to be an oil (liquid) then it would be the one with the longest carbon chain. This is because the bonding is strongest with these ones, making them need more energy to turn into a gas.
Volatility and flashpoint depend on the boiling point because it is the vapour of a liquid that ignites first, so the liquid must be gaseous first.
The stronger the bonding, the more viscous (thick) the liquid is.
Any molecules that have a H bonded to FON are soluble in water, due to hydrogen bonding. Solubility decreases as carbon chain length increases.

Branched molecules have lower boiling points than their respective straight-chained isomer. This is because the molecules can't pack together as tightly (which would require more energy to break the intermolecular bonds).

sweetiepi

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Re: VCE Chemistry Question Thread
« Reply #8071 on: July 22, 2019, 07:50:27 pm »
0
Could someone please check this section of my organic notes and point out any inaccuracies? Thank you!

--------

saturated: all single bonds between carbon atoms
unsaturated: has double or triple bonds between carbon atoms

A homologous series is a group of organic chemical compounds that have similar structures which differ only by the number of CH2 units in the main carbon chain. They have similar chemical properties but different physical properties.

The longer the carbon chain:
   • the higher the boiling point
   • the higher the flashpoint (how soon a liquid becomes volatile)
   • the higher the volatility
   • the higher the viscosity
   • the lower the solubility

These are because the longer the chain, the higher the chance for an uneven distribution of electrons, increasing the strength of bonding via dipole-dipole forces.
If you were given a list of hydrocarbons and asked which was most likely to be an oil (liquid) then it would be the one with the longest carbon chain. This is because the bonding is strongest with these ones, making them need more energy to turn into a gas.
Volatility and flashpoint depend on the boiling point because it is the vapour of a liquid that ignites first, so the liquid must be gaseous first.
The stronger the bonding, the more viscous (thick) the liquid is.
Any molecules that have a H bonded to FON are soluble in water, due to hydrogen bonding. Solubility decreases as carbon chain length increases.

Branched molecules have lower boiling points than their respective straight-chained isomer. This is because the molecules can't pack together as tightly (which would require more energy to break the intermolecular bonds).
I had a quick skim, looks a-okay to me! :)
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antigony

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Re: VCE Chemistry Question Thread
« Reply #8072 on: July 22, 2019, 09:27:33 pm »
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I had a quick skim, looks a-okay to me! :)

Great, thanks so much :)

pugs

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Re: VCE Chemistry Question Thread
« Reply #8073 on: July 22, 2019, 10:32:39 pm »
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hey! just wanted to check my answer:

would i be right in saying that the mass of a polymer is the same as the total mass of the monomers that make it up, as nothing new is added? (or does the breaking of the double bond make a difference?)

thanks very much! :)


2019 vce journal here

sweetcheeks

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Re: VCE Chemistry Question Thread
« Reply #8074 on: July 23, 2019, 01:24:07 pm »
+5
hey! just wanted to check my answer:

would i be right in saying that the mass of a polymer is the same as the total mass of the monomers that make it up, as nothing new is added? (or does the breaking of the double bond make a difference?)

thanks very much! :)

Depends on the polymer. If you are talking about addition polymerisation, then you can say that. However, it would be incorrect if you are talking about polymers in general, as condensation polymerisation results in the loss of a small molecule (e.g. HCl or H2O) and as a result will have a different mass than the combined monomer masses.

antigony

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Re: VCE Chemistry Question Thread
« Reply #8075 on: July 23, 2019, 09:04:41 pm »
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A couple of reaction pathways questions:

- Is a catalyst (AlCl3) needed when reacting an alkene with HCl to produce a chloroalkane?
- When combining a haloalkane and ammonia, is the ammonia in a concentrated solution with ethanol? If yes, must ammonia also be in a solution with ethanol when turning a primary alcohol into an amine via substitution?

Thanks!
« Last Edit: July 23, 2019, 09:06:31 pm by antigony »

pugs

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Re: VCE Chemistry Question Thread
« Reply #8076 on: July 23, 2019, 09:24:56 pm »
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Depends on the polymer. If you are talking about addition polymerisation, then you can say that. However, it would be incorrect if you are talking about polymers in general, as condensation polymerisation results in the loss of a small molecule (e.g. HCl or H2O) and as a result will have a different mass than the combined monomer masses.
oh i forgot about condensation polymerisation – thanks! :)


2019 vce journal here

redpanda83

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Re: VCE Chemistry Question Thread
« Reply #8077 on: July 24, 2019, 12:17:06 am »
+1
A couple of reaction pathways questions:

- Is a catalyst (AlCl3) needed when reacting an alkene with HCl to produce a chloroalkane?
- When combining a haloalkane and ammonia, is the ammonia in a concentrated solution with ethanol? If yes, must ammonia also be in a solution with ethanol when turning a primary alcohol into an amine via substitution?

Thanks!
I dont think a catalyst is required for halogenation of alkenes.
correct me if i am wrong, you cant directly convert alcohol into amine. And yeah concentrated ammonia in ethanol is used to make amines from haloalkanes. like think about it if ammonia and alcohol reacted why would we put them together in this scenario.
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antigony

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Re: VCE Chemistry Question Thread
« Reply #8078 on: July 24, 2019, 06:57:41 pm »
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I dont think a catalyst is required for halogenation of alkenes.
correct me if i am wrong, you cant directly convert alcohol into amine. And yeah concentrated ammonia in ethanol is used to make amines from haloalkanes. like think about it if ammonia and alcohol reacted why would we put them together in this scenario.

Thank you for the confirmation about ethanol! I'm pretty sure you can convert an alcohol into an amine though - my teacher has it written in some notes she gave us, and a couple of people from other schools have also confirmed that reaction exists.

redpanda83

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Re: VCE Chemistry Question Thread
« Reply #8079 on: July 24, 2019, 07:18:43 pm »
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Thank you for the confirmation about ethanol! I'm pretty sure you can convert an alcohol into an amine though - my teacher has it written in some notes she gave us, and a couple of people from other schools have also confirmed that reaction exists.
cool. Yeeeee, just remembered you can do it, but its not employed in labs cause hard to control.
direct alkylation of ammonia
R−CH2OH⟶R−CH2NH2
should an acidic medium be used in this case?
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jnlfs2010

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Re: VCE Chemistry Question Thread
« Reply #8080 on: July 27, 2019, 08:05:54 pm »
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Do we need to know about each vitamin and where it is sourced?
Do we need to know about all the carbohydrates and where they are sourced?

Thanks
VCE:
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Rom_Dog

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Re: VCE Chemistry Question Thread
« Reply #8081 on: July 28, 2019, 11:41:14 am »
+4
Do we need to know about each vitamin and where it is sourced?
Do we need to know about all the carbohydrates and where they are sourced?

Thanks

From the VCAA study design on vitamins and carbohydrates:

"Vitamins: inability of humans to synthesise most vitamins (except Vitamin D) making them essential dietary
requirements; comparison of structural features of Vitamin C (illustrative of a water-soluble vitamin) and Vitamin D
(illustrative of a fat-soluble vitamin) that determine their solubility in water or oil."

"Carbohydrates: formation of disaccharides from monosaccharides, and of complex carbohydrates (specifically
starch and cellulose) as condensation polymers of monosaccharides; glycosidic links; storage of excess
glucose in the body as glycogen; comparison of glucose, fructose, sucrose and the artificial sweetener
aspartame with reference to their structures and energy content."

In my opinion the key characteristics you need to know about vitamins is that they are needed by the body in small amounts and thus considered micronutrients. Vitamin D and C are commonly used as examples so it benefits you to be familiar with these. Their structures are provided in the data book so there is no need to memorise them however you should know that the presence of hydroxyl groups contributes to the solubility of vitamin C while Vitamin D is largely non-polar and not water soluble (stored in fat).

With carbs, I think it's good to know that polysaccharides form through condensation reactions (H2O as by product) and that starch, cellulose and glycogen are polymers of glucose. Sometimes you'll be asked to name a glycosidic link too.

It's best to refer to the study design for exam study but stick to what you are taught in class for your SACs because teachers may give you questions that require the application of the concepts taught to you in the classroom. Hope this helps!!  :D

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JR_StudyEd

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Re: VCE Chemistry Question Thread
« Reply #8082 on: July 30, 2019, 04:33:00 pm »
+1
I need help with the VCAA 2014 Chem exam, Q2 from Section B. It looks really intimidating and I don't feel like I know enough about reaction pathways to be able to even start off. An explanation of how the diagram works would also be helpful, as I know VCAA like to throw these kinds of questions into exams (and will very likely do so again this year).
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redpanda83

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Re: VCE Chemistry Question Thread
« Reply #8083 on: July 30, 2019, 05:40:36 pm »
+1
I need help with the VCAA 2014 Chem exam, Q2 from Section B. It looks really intimidating and I don't feel like I know enough about reaction pathways to be able to even start off. An explanation of how the diagram works would also be helpful, as I know VCAA like to throw these kinds of questions into exams (and will very likely do so again this year).
Ethene -> ethanol -> ethanoic acid                                       
prop-1-ene -> 1-chloropropane -> propan-1-ol                         ethanoic acid + propan-1-ol -> propylethanoate
                                |
                          propan-1-amine
use the attachment
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Sine

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Re: VCE Chemistry Question Thread
« Reply #8084 on: July 30, 2019, 08:02:33 pm »
+3
I need help with the VCAA 2014 Chem exam, Q2 from Section B. It looks really intimidating and I don't feel like I know enough about reaction pathways to be able to even start off. An explanation of how the diagram works would also be helpful, as I know VCAA like to throw these kinds of questions into exams (and will very likely do so again this year).
The ester pathway is a very important pathway within the context of VCE. You would definitely want to learn thoroughly to the point of memorisation of the whole pathway - including reactants/products and catalysts requried to convert stuff to an alcohol/carboxylic acid and combine them to get an ester.