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March 28, 2024, 08:31:08 pm

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Syndicate

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Re: VCE Chemistry Question Thread
« Reply #4800 on: March 01, 2016, 10:00:32 pm »
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YEAR 11 CHEMISTRY QUESTION

Hi all! Having a bit of trouble with chemistry, and this question in particular  :P

Find the identity of an atom given the following electronic configuration.
1s^2 2s^2 2p^6 3s^2 3p^4

I know that the number of valence electrons is equal to the group number. So in this case, it's group 4? But per my understanding, Sulfur is in group 6?

I am incredibly confused- please help out!  :-\

In schrodinger's model, each orbital can hold upto a maximum of two electrons.

s has 1 orbital
p has 3 orbitals
d has 5 orbitals
f has 7 orbitals

The litlle subscript at the top tells you the amount of electrons the sub shell holds. (E.g. 3p^5 holds 5 electrons)

In your case, the first shell holds 2 electrons, the seconds one holds 8 (2s^2 and 2p^6), and finally the third one holds 6 electrons (3s^2 and 3p^4)

You would add the amount of electrons there are in all your shells, and in your case, you would have 16 electrons.

There are 6 valence electrons (as there are 6 electrons in the third shell), therefore it would be found in Group 6 (or 16...), and your atom would be Sulfur.
« Last Edit: March 01, 2016, 10:03:03 pm by Syndicate »
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Re: VCE Chemistry Question Thread
« Reply #4801 on: March 01, 2016, 10:15:26 pm »
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Thank you so much Syndicate  ;D

I understand everything but still am lost when say that the atom has to be in Group 6 or 16. I know that the number of valence electrons (in this case 6) is equal to the group number, but where does Group 16 come from?

Syndicate

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Re: VCE Chemistry Question Thread
« Reply #4802 on: March 01, 2016, 10:22:31 pm »
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Thank you so much Syndicate  ;D

I understand everything but still am lost when say that the atom has to be in Group 6 or 16. I know that the number of valence electrons (in this case 6) is equal to the group number, but where does Group 16 come from?



I am sure that this table will be able to assist you.
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Re: VCE Chemistry Question Thread
« Reply #4803 on: March 01, 2016, 10:42:38 pm »
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Thank you for all your help Syndicate- so speedy  :P

I think I'm missing a fundamental area of knowledge for groups in periodic tables though! I am incredibly confused as to why Group 16 was included too.

Another example: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^8. Is this atom in Group 2 because of 4s^2? I thought it was Nickel because it's in Group 2 and Period 4 but the answer says Calcium which is not in Group 2!!

Feeling very lost..

lzxnl

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Re: VCE Chemistry Question Thread
« Reply #4804 on: March 01, 2016, 10:46:01 pm »
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Thank you for all your help Syndicate- so speedy  :P

I think I'm missing a fundamental area of knowledge for groups in periodic tables though! I am incredibly confused as to why Group 16 was included too.

Another example: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^8. Is this atom in Group 2 because of 4s^2? I thought it was Nickel because it's in Group 2 and Period 4 but the answer says Calcium which is not in Group 2!!

Feeling very lost..

Wait. What!? This is in group 10 because of the 3d8. Add the 2 4s electrons and the 8 3d electrons to get 10. You do this because the 4s and 3d energy levels are very close and they behave as a whole valence shell.
By the way, calcium is in group 2, but it's not the right answer.
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Re: VCE Chemistry Question Thread
« Reply #4805 on: March 01, 2016, 10:58:16 pm »
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Hey lzxnl!  :D

Oohh I understand that much better now, thank you  :D

Sorry for the confusion- I meant to say Nickel when I said Calcium and Calcium when I said Nickel  :-\

When we add valence electrons to find the group number, I noticed that you said to add 4s and 3d, even though they don't have the same shell number. Or do they..? It's usually adding shell 1/ 2/ 3, etc. When do you add those different shell numbers? Is that the only case?

Hope that made a bit of sense- thank you guys for all your help so late  ;D

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Re: VCE Chemistry Question Thread
« Reply #4806 on: March 01, 2016, 11:01:24 pm »
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Hey lzxnl!  :D

Oohh I understand that much better now, thank you  :D

Sorry for the confusion- I meant to say Nickel when I said Calcium and Calcium when I said Nickel  :-\

When we add valence electrons to find the group number, I noticed that you said to add 4s and 3d, even though they don't have the same shell number. Or do they..? It's usually adding shell 1/ 2/ 3, etc. When do you add those different shell numbers? Is that the only case?

Hope that made a bit of sense- thank you guys for all your help so late  ;D

Honestly, the whole shell thing is a bit confusing if you don't take a bit more of a thorough look into the atom's quantum numbers (and have a small quantum mechanics lecture). You're best off just adding up all the electrons to get the atomic number, and use that to find the element.

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Re: VCE Chemistry Question Thread
« Reply #4807 on: March 01, 2016, 11:03:46 pm »
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Honestly, the whole shell thing is a bit confusing if you don't take a bit more of a thorough look into the atom's quantum numbers (and have a small quantum mechanics lecture). You're best off just adding up all the electrons to get the atomic number, and use that to find the element.

Yeah. That method is more foolproof, if not a bit longer.
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Re: VCE Chemistry Question Thread
« Reply #4808 on: March 01, 2016, 11:12:21 pm »
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Awesome! Really appreciate all your help, don't know how I'd be managing chem without it  :P

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Re: VCE Chemistry Question Thread
« Reply #4809 on: March 03, 2016, 09:52:44 pm »
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Quick Question, In a back titration with standard sodium hydroxide added in excess to the solution with ammonium... When you boil the solution to evaporate all of the ammonia. Why do you need to keep adding water and keep a constant volume? Is it so the solution doesn't go dry?
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Re: VCE Chemistry Question Thread
« Reply #4810 on: March 04, 2016, 12:23:12 am »
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Quick Question, In a back titration with standard sodium hydroxide added in excess to the solution with ammonium... When you boil the solution to evaporate all of the ammonia. Why do you need to keep adding water and keep a constant volume? Is it so the solution doesn't go dry?

Depends - what else is in the solution? What's the context of the reaction? It could very easily be because you want all the water to evaporate off, but it could also be for reasons that's not explained in VCE chemistry - for example, maybe at higher concentrations, the sodium hydroxide causes something else in the solution to form a different compound, and so you maintain the water level to stop the concentration from reaching the tipping point.

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Re: VCE Chemistry Question Thread
« Reply #4811 on: March 06, 2016, 09:37:19 pm »
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Could someone explain why you should rinse the burette in a titration with solution and not de-ionised water ? I know that the overall concentration will increase , but why ?


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Re: VCE Chemistry Question Thread
« Reply #4812 on: March 08, 2016, 10:05:54 am »
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Could someone explain why you should rinse the burette in a titration with solution and not de-ionised water ? I know that the overall concentration will increase , but why ?

As I understand it:

When you rinse the burette with water, some water molecules will remain after washing. When the burette is subsequently filled with titrant, that titrant will be slightly diluted by the water molecules. This means that a larger volume of titrant will be required to reach the endpoint of the reaction, with a higher than intended average titre utilised in calculations. As this inadvertent dilution is not factored into calculations, it will instead be 'assumed' that the substance being analysed has a higher concentration that it actually does, as it theoretically required a higher titre to reach the endpoint.

In terms of calculations: higher average titre means higher mole of titrant, means higher mole (through ratios) of solution (unknown conc) means higher concentration of solution calculated.

Sorry for the convoluted explanation, I'm trying to get my head around chem myself... ;)

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Re: VCE Chemistry Question Thread
« Reply #4813 on: March 09, 2016, 07:02:37 pm »
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Hey guys, so if a question says that the yield of a product is 85%, and if the reactant would have used 2g for 100% yield, but since it's 90% yield what's the mass required of the reactant?

I.e.. A + B --> C
2g of A should result in 4g of C. But there was only an 90% yield, so what mass of A is required?
Is it 2/0.9 or is it 2 * 100/90 (coz I think it's the former but worked solutions had the latter)
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Re: VCE Chemistry Question Thread
« Reply #4814 on: March 09, 2016, 07:14:17 pm »
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I.e.. A + B --> C
2g of A should result in 4g of C. But there was only an 90% yield, so what mass of A is required?
Is it 2/0.9 or is it 2 * 100/90 (coz I think it's the former but worked solutions had the latter)

I think 2/0.9 and 2*100/90 is the same thing
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