[ctpengage]

0.130g of a sample of impure iron was dissolved in excess dilute sulfuric acid to form iron (II) sulfate. This was then titrated with a 0.0137 mol dm^-3 solution of dichromate ions (Cr₂O₇^2- and was found to be just sufficient to reduce 27.3cm³ of the solution to chromium (III) ions (Cr³⁺).
The balanced ionic equation for the titration reaction is:

6Fe²⁺(aq) + Cr₂O₇^2-(aq) + 14H⁺(aq) ---> 6Fe³⁺ + 2Cr³⁺(aq) + 7 H₂O(l).

However I don't understand how it was formed from the information given. Where did the H⁺ ions come from, and why the hydrogen ions are needed. Also if possible could anyone tell me which were the spectator ions and so on. I'm getting really confused.

[Borek]

This reaction takes place in acidic conditions. Quite often these things are neglected in questions - you are supposed to assume that reaction given is correct and that spectator ions are there - as long as they are spectators, what difference does it make what they are?