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

1. 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?
2. Make half eqns for each reaction
3. (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
4. (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
5. (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 I'm so nervous for this exam as well
6. (Original post by blueangel328)
OMGGGG how did I miss that???! THANK YOUUUU so much, it's been a long day for me I'm so nervous for this exam as well
Haha no problem! Good luck with the upcoming exam.
7. (Original post by corpeal)
Haha no problem! Good luck with the upcoming exam.
Thanks Good luck to you too in any exams you're taking!!
8. (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?
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?
9. (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

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