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Help with a question from 6ch05/01 june 2010 please

When dichromate ions (VI) ions, Cr2O7 2- , react with iron (II) ions in acidic solution, the products are chromium (III) ions and iron (III) ions. In what ratio do the dichromate (VI) ions and the iron (II) ions react?

A 1:6
B 1:5
C 2:5
D 1:3

I initially thought this would be a simple question, maybe I'm missing something?
Thanks in advance!
Reply 1
Make half eqns for each reaction
Original post by corpeal
Make half eqns for each reaction


Hey! What I've done is written the ionic equation fully and it comes out at a 1:1 ratio? I have written as follows:

Cr2O7 2- + Fe2+ + 14H+ + 5e- GOING TO 2Cr3+ + Fe3+ + 7H2O
Reply 3
Original post by blueangel328
Hey! What I've done is written the ionic equation fully and it comes out at a 1:1 ratio? I have written as follows:

Cr2O7 2- + Fe2+ + 14H+ + 5e- GOING TO 2Cr3+ + Fe3+ + 7H2O



The full ionic equation must not contain electrons. One of the half equations must be multiplied by a number so that when they are combined, the electrons cancel. I.e. same number of electrons in the reactants and products
Original post by corpeal
The full ionic equation must not contain electrons. One of the half equations must be multiplied by a number so that when they are combined, the electrons cancel. I.e. same number of electrons in the reactants and products


OMGGGG how did I miss that???! THANK YOUUUU so much, it's been a long day for me :frown: I'm so nervous for this exam as well
Reply 5
Original post by blueangel328
OMGGGG how did I miss that???! THANK YOUUUU so much, it's been a long day for me :frown: I'm so nervous for this exam as well


Haha no problem! Good luck with the upcoming exam.
Original post by corpeal
Haha no problem! Good luck with the upcoming exam.


Thanks :smile: Good luck to you too in any exams you're taking!!
Original post by blueangel328
When dichromate ions (VI) ions, Cr2O7 2- , react with iron (II) ions in acidic solution, the products are chromium (III) ions and iron (III) ions. In what ratio do the dichromate (VI) ions and the iron (II) ions react?

A 1:6
B 1:5
C 2:5
D 1:3

I initially thought this would be a simple question, maybe I'm missing something?
Thanks in advance!


These are the half equations:

Cr2O72- + 14H+ + 6e --> 2Cr3+ + 7H2O

Fe2+ --> Fe3+ + 1e

Now can you see the ratio in which they have to react?
Original post by charco
These are the half equations:

Cr2O72- + 14H+ + 6e --> 2Cr3+ + 7H2O

Fe2+ --> Fe3+ + 1e

Now can you see the ratio in which they have to react?


YES! I get it now thank you :wink:

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