Write the equation " oxidising iron(II) to iron(III) ions using a solution containing Cr2O7^2- ions, acidified with dilute sulphuric acid; the chromium ends up as Cr^3+ ions "
6Fe^2+ + Cr2O7^2- + 14H^+ ---> 6Fe^3+ + 2Cr^3+ + 7H2O
I understand everything in the answer, EXCEPT for where the number 6 comes from that are in front of the irons.
Can someone please help me out?
Which unis have sent theirs?