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# A-level Chemistry Revision Squad! watch

1. (Original post by Hunnybeebee)
I need to look at the diagram properly :'( look like a fool lol

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Lol, do you know if mines correct though?

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2. Photochlorination is killing me
3. Hi,
On mass spectrometry how do do you know which one the Molecular ion is? For example on this one the book says the Mr would be 86, but I would of said 85 because that's the large peak? Or is it always the peak that is the most to the right hand side?
Cheers
4. Can someone explain how you do Question 2. Thanks

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5. QUOTE=Farmerjj;65075469]Hi,On mass spectrometry how do do you know which one the Molecular ion is? For example on this one the book says the Mr would be 86, but I would of said 85 because that's the large peak? Or is it always the peak that is the most to the right hand side?
Cheers[/QUOTE]
The molecular ion peak would be 100. As it is normally the biggest mass peak and gives relative molecular mass
6. (Original post by TeaAndTextbooks)
Can someone explain how you do Question 2. Thanks

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The mole ratio between CxHy : CO2
50: 350
1 : 7

Hence there must be 7 carbons to balance both side. Therefore the answer is C7H16
7. (Original post by Sandy_Vega30)
The mole ratio between CxHy : CO2
50: 350
1 : 7

Hence there must be 7 carbons to balance both side. Therefore the answer is C7H16
The answer is C though but I understand what your saying. Thank you

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8. For ligand exchange, how do I know how many ligands get exchanged. For example, if I had Fe(H^2O)6 reacting with excess OH-, is there a way to find out if only 1 ligand is exchanged, maybe 2 or 3 etc?
9. (Original post by TeaAndTextbooks)
The answer is C though but I understand what your saying. Thank you

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This is a June 2012 paper. The answer is B not C.
10. (Original post by Glavien)
Lol, do you know if mines correct though?

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I would say it's 3-methyl butyl 2-methyl propanoate? Because when naming the alcohol, the longest chain is 4 carbons? So would the alcohol be 3-methyl butan-2-ol? But then I'm not sure how naming works with easters when using secondary/tertiary alcohols since the alcohol part becomes an alkyl group.
11. (Original post by Sandy_Vega30)
This is a June 2012 paper. The answer is B not C.
Oh yeah it is sorry. It's no wonder I was so confused lol. I was stuck on that answer for ages but I was checking the wrong answer all along hahahaa. Thank you so much.

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12. (Original post by TeaAndTextbooks)
Oh yeah it is sorry. It's no wonder I was so confused lol. I was stuck on that answer for ages but I was checking the wrong answer all along hahahaa. Thank you so much.

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Would someone be able to name this for me: CH3(CH2)2CH2CH2OH? It's just that the brackets confuse me.
Thanks
13. (Original post by Farmerjj)
Would someone be able to name this for me: CH3(CH2)2CH2CH2OH? It's just that the brackets confuse me.
Thanks
Try drawing it out so you can see what it looks like
14. (Original post by Farmerjj)
Would someone be able to name this for me: CH3(CH2)2CH2CH2OH? It's just that the brackets confuse me.
Thanks
Anything in the brackets belongs to the carbon in the left. But in your question, the carbon in the left already has 3 hydrogens. I think you made a mistake somewhere, could you recheck? I can help then.
15. (Original post by Sandy_Vega30)
Anything in the brackets belongs to the carbon in the left. But in your question, the carbon in the left already has 3 hydrogens. I think you made a mistake somewhere, could you recheck? I can help then.
I'm not sure, that's what it said in the book.
16. (Original post by Farmerjj)
Hi,
On mass spectrometry how do do you know which one the Molecular ion is? For example on this one the book says the Mr would be 86, but I would of said 85 because that's the large peak? Or is it always the peak that is the most to the right hand side?
Cheers
The tallest peak is called the base peak and its the most STABLE fragment.
Yes, the molecular ion peak is always the one furtherest to the right. This represents the UN-FRAGMENTED molecule minus one electron.

However, be careful as there could be isotopes present and this could give you an M+1 peak. However, you will know if this is the Molecular ion peak or not as the the molecular ion peak should be greater than the M+1 peak (isotope peak)

Hope this helped, ask me to clarify more if it doesn't!

17. (Original post by Marco1000)
For ligand exchange, how do I know how many ligands get exchanged. For example, if I had Fe(H^2O)6 reacting with excess OH-, is there a way to find out if only 1 ligand is exchanged, maybe 2 or 3 etc?
It really depends if the substance you are adding is in excess or not.

If only a few drops of OH ions are added then some of the H20 ligands will be replaced, if however, the OH ions are in excess, then all the ligands will be replaced.

Eg. In [Fe(H20)6] the charge is +2. Therefore you add 2OH, and you end up with [Fe(H20)4(OH)2] which is a precipitate and 2H20 is also produced. (You add the same amount of OH ions as the charge of the ion and you make this number of water molecules also)

As the Iron precipitate does not dissolve in excess OH ions, then this precipitate will remain even in excess.

However, the likes of Cobalt produces a blue precipitate in OH ions and dissolves in excess giving a yellow solution. The equations look like this:

[Co(H20)6] +2 + 2OH ------------- [Co(h20)4(oh)2] (solid) + 2H20

in excess the equation is:

[Co(H20)4(oh)2] + 4OH -------the-----[Co(OH)6] -4 charge + 4H20

The overall charge is -4 as Cobalt has a charge of +2 and we added 6OH- ions and so +2-6 = -4!

Hope i helped!
18. (Original post by Farmerjj)

I'm not sure, that's what it said in the book.
Which paper is that?
19. (Original post by CERC)
The tallest peak is called the base peak and its the most STABLE fragment.
Yes, the molecular ion peak is always the one furtherest to the right. This represents the UN-FRAGMENTED molecule minus one electron.

However, be careful as there could be isotopes present and this could give you an M+1 peak. However, you will know if this is the Molecular ion peak or not as the the molecular ion peak should be greater than the M+1 peak (isotope peak)

Hope this helped, ask me to clarify more if it doesn't!

Hey, can you please explain a little further on the M+1peak, like for Cl2, there is Cl(35) and Cl(37) so which one would be for the M+1 peak ?

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The concentration of iron(II) ions in aqueous solution can be determined by titrating the solution, after acidification, with a standard solution of potassium manganate(VII).

(i) Explain, by reference to the data given in the table above, why hydrochloric acid should not be used to acidify the solution containing iron(II) ions.

(ii) Explain, by reference to the data given in the table above, why nitric acid should not be used to acidify the solution containing iron(II) ions.

i) MnO4 -/Mn2+ has a more positive Eο value than Cl2/Cl– and will oxidise Cl– or change Cl– to Cl2

(ii) NO3-/HNO3 has a more positive Eο value than Fe3+/Fe2+ and will oxidise Fe2+ or changeFe2+ to Fe3+

BUT what I'm confused on is can't the answers be the other way round too since the electrode potential for Cl2/cl- is greater than that of Fe3+/Fe2+ so could have the same answer as part ii, and similarly Mno4-/mn2+ has a great a potential than No3-/HNO3 so could have the same answer to part i?

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