VCE Chemistry Question Thread

[jnlfs2010]

Biodiesel by itself is not classified as a fatty acid right?
Rather it’s made up of long ester molecules which are classified as fatty acids?
I’m a bit stumped about this...

Biodiesel is not a fatty acid.
Biodiesel is made up of long ester molecules that are methyl/ethyl esters (these methyl and ethyl esters are produced by reacting fatty acids such as stearic acid with methanol in the presence of like a KOH catalyst)

Fatty Acids all have COOH which esters do not

[Bri MT]

Biodiesel by itself is not classified as a fatty acid right?
Rather it’s made up of long ester molecules which are classified as fatty acids?
I’m a bit stumped about this...

Biodiesel is composed of fatty acid methyl/ethyl esters  (a type of ester made from fatty acids). Biodiesel is not itself a fatty acid (it's also made up of a range of molecules, not just one)

Fatty Acids all have COOH which esters do not

Your answer is mostly correct however some esters do have COOH e.g. aspirin (acetylsalicylic acid)

[IThinkIFailed]

Thanks for the help!

Is this correct?
The longer the molecule, the more polar it is?
And if this is right, is it because there is more electronegativity difference and thus greater chance for dipoles to form?

[Bri MT]

Thanks for the help!

Is this correct?
The longer the molecule, the more polar it is?
And if this is right, is it because there is more electronegativity difference and thus greater chance for dipoles to form?

A longer molecule will have greater dispersion forces (attractions caused by temporary dipoles) however I would not say that a longer molecule is more polar. In fact, longer molecules often have longer non-polar regions in comparison to polar regions.

[caffinatedloz]

Hey guys! Can someone explain how to convert cm to nanometres. Like I've tried doing worked examples and practice questions but I just don't get it. Is there a good way of remembering it?

[sk2000]

Hey guys! Can someone explain how to convert cm to nanometres. Like I've tried doing worked examples and practice questions but I just don't get it. Is there a good way of remembering it?

Multiply the number in cm by 10^-7. There's a conversion table in the data booklet too

[vox nihili]

Hey guys! Can someone explain how to convert cm to nanometres. Like I've tried doing worked examples and practice questions but I just don't get it. Is there a good way of remembering it?

A centimetre is 100th of a metre. A nanometre is one billionth of a metre.

To make it easier for yourself, divide the number of centimetres by 100 to give yourself the number in metres.

Then multiply it by one billion (i.e. 1,000,000,000) to get the number of nanometres.

Multiply the number in cm by 10^-7. There's a conversion table in the data booklet too

You can also do this, but it should be 10⁷ not 10^-7

[caffinatedloz]

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//

Thank you both! Does that mean that

1.35 cm would be:
(1.35/100) * 1,000,000 = 13500nm

which would be 1.35 * 10^7 in scientific notation?

[angrybiscuit]

Thank you both! Does that mean that

1.35 cm would be:
(1.35/100) * 1,000,000 = 13500nm

which would be 1.35 * 10^7 in scientific notation?

Yes that's correct!

I remembered it by 'hopping' across each interval. So cm to mm is x10. mm to µm is x1000. µm to nm is x1000. So I just jump between them when converting which was easier for me to understand and remember!

Someone pls correct me if I'm wrong! It's been a while ah..

[SmartWorker]

Hey!

I am a bit confused about Schrodinger model, why does the 4th shell fill in before the 3rd.

So if I recall right:
1s^2. 2s^2. 2p^6. 3s^2. 3p^6. then 4s^2. 3d^10.

It says in the textbook that 4s^2 is lower in energy than 3d^6. But if this the case, shouldn't 3s^2 be lower in energy than 2p^6???

Thank you so much.

Hey guys! Can someone explain how to convert cm to nanometres. Like I've tried doing worked examples and practice questions but I just don't get it. Is there a good way of remembering it?

I kind of like to think of it as: (this is a very basic understanding but...)

cm - is much large than a nanometer.

Conversion table:
1 cm = 10 mm
1mm = 1000 µm
1µm = 1000nm

Therefore, 1cm = 1 x 10^7.   (this comes from adding all 0s ie. 1+3+3)

Example: 8.35 cm to nm

8.35cm = 83500000nm
 Using Scientific notation --> 8.35 x 10^7 (because the decimal must 'jump' 7 places to the right {through multiply)

Hope this helps.


Mod edit: Merged double post

[IThinkIFailed]

Hey guys,
I’m struggling to understand how increasing temperature increases the volume of a gas. Is it because the gas particles move quicker due to higher average kinetic energy, and as a result they kind of “expand” and become more widely spaced; occupying more space in the process and increasing its volume?

[Sine]

Hey guys,
I’m struggling to understand how increasing temperature increases the volume of a gas. Is it because the gas particles move quicker due to higher average kinetic energy, and as a result they kind of “expand” and become more widely spaced; occupying more space in the process and increasing its volume?

You are definitely on the right track.
- Increasing the temperature increases the average kinetic energy of these gas particles.
- The increased kinetic energy means that the gas particles hit the surface of the container they are in with a greater force.
- As the surface is being hit by increasing force - if this contained can expand it will
- The volume then increases in order to attempt to maintain the original pressure

[Bri MT]

Hey!

I am a bit confused about Schrodinger model, why does the 4th shell fill in before the 3rd.

So if I recall right:
1s^2. 2s^2. 2p^6. 3s^2. 3p^6. then 4s^2. 3d^10.

It says in the textbook that 4s^2 is lower in energy than 3d^6. But if this the case, shouldn't 3s^2 be lower in energy than 2p^6???

Thank you so much.

I understand why you would think that s should be either always lower than p or always higher than it but that isn't the case. this page is more at 1st year uni level rather than yr 11 chem level but the diagrams may help. Please also note that the energy levels implied by the diagrams aren't absolute and change as orbitals are filled - which means you end up with things like the copper and chromium exception.

[radiant roses]

Hello,

Is this organic compound named as 'fluoro-prop-1-ene', or '1-methyl fluoroethene'.
When naming, do you take into consideration the fact that the longest carbon chain is 3, or that there is a CH3 attached to one of the carbons?

[ArtyDreams]

Hello,

Is this organic compound named as 'fluoro-prop-1-ene', or '1-methyl fluoroethene'.
When naming, do you take into consideration the fact that the longest carbon chain is 3, or that there is a CH3 attached to one of the carbons?

Hi!

Not really sure if I'm right, but I'm thinking it is 2-Fluoropropene.

The longest carbon chain is 3, making it propene, and the fluorine is added on the second carbon