A-level Chemistry Revision Squad!
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Original post by shiney101
Can someone help me out please?
When CrO4 2- reacts with H+ ions to form Cr2O7 2- what do you call that? Is it reduction?
When CrO4 2- reacts with H+ ions to form Cr2O7 2- what do you call that? Is it reduction?
Oxidation state of Cr in CrO4 2- is +6.
Oxidation state of Cr in Cr2O7 2- is +6
Therefore not a redox reaction
Original post by SamuelN98
Do either of you have the answers to the questions from the practical book?
i cant find them anywhere.
i cant find them anywhere.
They could be on Maths and Physics Tutor? I've never looked for them if I'm honest.. 🙊
Original post by farihak97
Hi,
Need major help on redox please and free radical substitution, i don't understand it at all, how do you work it out?
Thanks
x
Need major help on redox please and free radical substitution, i don't understand it at all, how do you work it out?
Thanks
x
What do you need to know about it?
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Original post by SamuelN98
Oxidation state of Cr in CrO4 2- is +6.
Oxidation state of Cr in Cr2O7 2- is +6
Therefore not a redox reaction
Oxidation state of Cr in Cr2O7 2- is +6
Therefore not a redox reaction
So what would you call this reaction?
Original post by shiney101
So what would you call this reaction?
I don`t know exactly as its not on my syllabus, i was just making an educated guess. I think you would call it an equilibrium reaction.
This may help.
http://www.slideshare.net/pieferrer/chromate-dichromate-equilibrium
(edited 8 years ago)
Original post by kiiten
Hi,
It's just general, i don't understand how to make the overall equations in redox, i struggle with it, i can do the first half equation bit for example,
Al+3 -> Al+ + 3e- , however i am unable to do the overall equations could you give some examples and explain on how to do it please.
Thank you Kitten
x
Original post by farihak97
Hi,
It's just general, i don't understand how to make the overall equations in redox, i struggle with it, i can do the first half equation bit for example,
Al+3 -> Al+ + 3e- , however i am unable to do the overall equations could you give some examples and explain on how to do it please.
Thank you Kitten
x
It's just general, i don't understand how to make the overall equations in redox, i struggle with it, i can do the first half equation bit for example,
Al+3 -> Al+ + 3e- , however i am unable to do the overall equations could you give some examples and explain on how to do it please.
Thank you Kitten
x
Yeah sure, ill try find some examples for tomorrow
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Original post by farihak97
Hi,
It's just general, i don't understand how to make the overall equations in redox, i struggle with it, i can do the first half equation bit for example,
Al+3 -> Al+ + 3e- , however i am unable to do the overall equations could you give some examples and explain on how to do it please.
Thank you Kitten
x
It's just general, i don't understand how to make the overall equations in redox, i struggle with it, i can do the first half equation bit for example,
Al+3 -> Al+ + 3e- , however i am unable to do the overall equations could you give some examples and explain on how to do it please.
Thank you Kitten
x
Consider the equations:
Cl2 + 2e- -----> 2Cl-
Fe2+ -------> Fe3+ + e-
Do you understand what is happening in both these half equations? If so how would you combine for a redox equation (ill tell you if you go wrong)
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A mixture of 1 mole of ethanoic acid, 2 moles of ethanoic and 1 mole of water was allowed to reach EQM. On analysis, the EQM mixture was found to contain 0.257 mole of ethanoic acid. Find Kc for the reaction...CH3C00H+C2H5OH----><----CH3C00C2H5+ H20
The answer I get is 1.31, my tutor says it's '4 something'. Please help
The answer I get is 1.31, my tutor says it's '4 something'. Please help
Okay, Thank you so much. Unfortunately i don't know how to do it.ACE- i know that i'm meant to look at the atom, then the charges and finally the electrons.Could you, please show me how to make the overall question with this question, I know the first part of the half equation, which isFe2+ Fe3+ + 1e-How do you work out the second half equation and the overall.Thank you so much for helping me Kiiten means a lotFe2+ + MnO4- Fe3+ + Mn2+Please help.
Original post by kiiten
Consider the equations:
Cl2 + 2e- -----> 2Cl-
Fe2+ -------> Fe3+ + e-
Do you understand what is happening in both these half equations? If so how would you combine for a redox equation (ill tell you if you go wrong)
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Cl2 + 2e- -----> 2Cl-
Fe2+ -------> Fe3+ + e-
Do you understand what is happening in both these half equations? If so how would you combine for a redox equation (ill tell you if you go wrong)
Posted from TSR Mobile
Original post by farihak97
Okay, Thank you so much. Unfortunately i don't know how to do it.ACE- i know that i'm meant to look at the atom, then the charges and finally the electrons.Could you, please show me how to make the overall question with this question, I know the first part of the half equation, which isFe2+ Fe3+ + 1e-How do you work out the second half equation and the overall.Thank you so much for helping me Kiiten means a lotFe2+ + MnO4- Fe3+ + Mn2+Please help.
No problem
I think you're getting the method confused. First, we need to balance the electrons in order to combine them to make a redox equation. Cl2 + 2e- -----> 2Cl- has 2e- but Fe2+ -------> Fe3+ + e- has 1 electron. So you need to multiply the second equation by 2 to get 2Fe2+ -------> 2Fe3+ + 2e-
Now you can combine the equations. Starting with the reactants: the 2e- cancel out (because they're on opposite sides of the arrow) leaving you with Cl2 + 2Fe2+ as the reactants. Same with the products, just add the 2Fe3+ + 2Cl-
This gives you a final equation of:
Cl2 + 2Fe2+ ------------> 2Fe3+ + 2Cl-
Make sense?
Thank you so much, that makes so much sense, i tried a few questions and i checked the answers and they were right. Thank you so so much.
Original post by kiiten
No problem
I think you're getting the method confused. First, we need to balance the electrons in order to combine them to make a redox equation. Cl2 + 2e- -----> 2Cl- has 2e- but Fe2+ -------> Fe3+ + e- has 1 electron. So you need to multiply the second equation by 2 to get 2Fe2+ -------> 2Fe3+ + 2e-
Now you can combine the equations. Starting with the reactants: the 2e- cancel out (because they're on opposite sides of the arrow) leaving you with Cl2 + 2Fe2+ as the reactants. Same with the products, just add the 2Fe3+ + 2Cl-
This gives you a final equation of:
Cl2 + 2Fe2+ ------------> 2Fe3+ + 2Cl-
Make sense?
I think you're getting the method confused. First, we need to balance the electrons in order to combine them to make a redox equation. Cl2 + 2e- -----> 2Cl- has 2e- but Fe2+ -------> Fe3+ + e- has 1 electron. So you need to multiply the second equation by 2 to get 2Fe2+ -------> 2Fe3+ + 2e-
Now you can combine the equations. Starting with the reactants: the 2e- cancel out (because they're on opposite sides of the arrow) leaving you with Cl2 + 2Fe2+ as the reactants. Same with the products, just add the 2Fe3+ + 2Cl-
This gives you a final equation of:
Cl2 + 2Fe2+ ------------> 2Fe3+ + 2Cl-
Make sense?
Original post by shiney101
So what would you call this reaction?
it is an equilibrium reaction because the ions exist in different solutions. The yellow chromate ion CrO42- is only stable in alkali solutions, while the orange dichromate ion Cr2O72- is stable in acid solutions (which is why you need to add H+ ions)
Just only found this thread! Got 280/300 AQA AS, need an A for uni offer
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I need help for these two questions. For the ∆H sol, I calculated it this way. -(-2526)-1890+641-801= +476 kJmol^-1. As for the second one, 476-2526=-2050kJmol^-1. However, the answers are (i) ∆Hosol = 641 – 801 = –160 kJ mol–1 [1] (ii) ∆Hohyd = (1890 – 2526 – 160)/2 = –398 kJ mol–1
Can anyone explain the mark scheme to me? I can't quite get it.
Original post by RMNDK
There are some mistakes in your equation of Co2+ with NH3.
You also might want to give the colour of [Co(H2O)6]2+ before it is oxidised by oxygen.
How come you haven't included the equation of Fe3+ with excess OH- ?
The precipitate will dissolve in concentrated NaOH.
You also might want to give the colour of [Co(H2O)6]2+ before it is oxidised by oxygen.
How come you haven't included the equation of Fe3+ with excess OH- ?
The precipitate will dissolve in concentrated NaOH.
Thankyou for your comments, I will edit the document. Plus I have just cross referenced Fe3+ with excess OH- in my CPG revision guide and it states it as 'no visible change' so I really don't know what to put to be honest.
(edited 8 years ago)
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