Chemistry help! Watch

ch0c0lat3
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K2Cr2O7 + 3H2C2O4 + H2SO4 → Cr2(SO4)3 + _H2O + 6CO2 + K2SO4

Q17: https://filestore.aqa.org.uk/sample-...1-QP-JUN16.PDF

Question is what is the reducing agent in this reaction.

So i know that the reducing agent donates electrons and itself gets oxidised but i just don't get it for this reaction.

Thank you
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ch0c0lat3
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anyone?
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BobbJo
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#3
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H2C2O4
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ch0c0lat3
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#4
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Could you explain the process please.
(Original post by BobbJo)
H2C2O4
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BobbJo
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(Original post by ch0c0lat3)
Could you explain the process please.
the reducing agent donates electrons and itself gets oxidised
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ch0c0lat3
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I get all that simple knowledge but I feel overwhelmed like how do i approach this question.
Which compound gains the electrons i dont get it.
Do I like assign oxidation numbers to every single element in the whole equation then what do i do.
(Original post by BobbJo)
the reducing agent donates electrons and itself gets oxidised
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meganadele1505
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#7
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You have to look at the oxidation states for 3H2C2O4 the carbon in it is +1.
But in CO2 the carbon is +4 so has lost electrons been oxidised reducing the chromium.




(Original post by ch0c0lat3)
K2Cr2O7 + 3H2C2O4 + H2SO4 → Cr2(SO4)3 + _H2O + 6CO2 + K2SO4

Q17: https://filestore.aqa.org.uk/sample-...1-QP-JUN16.PDF

Question is what is the reducing agent in this reaction.

So i know that the reducing agent donates electrons and itself gets oxidised but i just don't get it for this reaction.

Thank you
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BobbJo
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(Original post by ch0c0lat3)
I get all that simple knowledge but I feel overwhelmed like how do i approach this question.
Which compound gains the electrons i dont get it.
Do I like assign oxidation numbers to every single element in the whole equation then what do i do.
Yes you can find the oxidation number of each element in each compound
K+ and SO42- ions are spectator ions so they are not involved
Cr goes from +6 oxidation state to +3 oxidation state
C goes from +3 oxidation state to +4 oxidation state
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ch0c0lat3
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Thank you so muchh. One question
Cr2(SO4)3, that is not involved like you said but how would i find the oxidation number if i only know that oxygen is -2. Do i use the ions or?
(Original post by BobbJo)
Yes you can find the oxidation number of each element in each compound
K+ and SO42- ions are spectator ions so they are not involved
Cr goes from +6 oxidation state to +3 oxidation state
C goes from +3 oxidation state to +4 oxidation state
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BobbJo
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(Original post by ch0c0lat3)
Thank you so muchh. One question
Cr2(SO4)3, that is not involved like you said but how would i find the oxidation number if i only know that oxygen is -2. Do i use the ions or?
You know the sulfate ion is SO42-
The sum of oxidation numbers is the charge on the species
Let oxidation number of sulfur be s
s + 4 (-2) = -2
so s = +6
then we calculate that Cr in Cr2(SO4)2 has an oxidation number +3
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ch0c0lat3
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#11
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So we dont include the 3?
(Original post by BobbJo)
You know the sulfate ion is SO42-
The sum of oxidation numbers is the charge on the species
Let oxidation number of sulfur be s
s + 4 (-2) = -2
so s = +6
then we calculate that Cr in Cr2(SO4)2 has an oxidation number +3
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BobbJo
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(Original post by ch0c0lat3)
So we dont include the 3?
What do you mean?
In Cr2(SO4)3, if you want to calculate the oxidation number of Cr, then let oxidation number of Cr be x
then 2x + 3(-2) = 0
x = +3
since the charge on SO42- is -2
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ch0c0lat3
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#13
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Thank you so much man.
(Original post by BobbJo)
What do you mean?
In Cr2(SO4)3, if you want to calculate the oxidation number of Cr, then let oxidation number of Cr be x
then 2x + 3(-2) = 0
x = +3
since the charge on SO42- is -2
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Mr.noname
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The answer is B C2O42- the oxidation state of hydrogen is +1 on both sides , hence H+ is not included.
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ch0c0lat3
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#15
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so when do i?
(Original post by Mr.noname)
The answer is B C2O42- the oxidation state of hydrogen is +1 on both sides , hence H+ is not included.
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Mr.noname
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#16
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(Original post by ch0c0lat3)
so when do i?
If you are asking when the oxidation state of hydrogen changes then it only changes in metal hydrides (e.g. NaH oxidation state of hydrogen is -1, otherwise always +1)
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BobbJo
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#17
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Oxidation state of hydrogen also changes when going from molecular hydrogen to hydrogen in a compound e.g 3H2 + N2 -> 2NH3
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