chemistry a level

A student carried out an experiment to find the mass of FeSO4.7H2O in an impure sample, X.
The student recorded the mass of X. This sample was dissolved in water and made up to
250 cm3
of solution.
The student found that, after an excess of acid had been added, 25.0 cm3
of this solution
reacted with 21.3 cm3
of a 0.0150 mol dm–3 solution of K2Cr2O7
(a) Use this information to calculate a value for the mass of FeSO4.7H2O in the sample of
X

i cannot answer this question for the life of me. can someone help? thank you!

This is a redox titration.

The dichromate ions are an oxidising agent that changes iron(II) to iron(III).

You need to generate the balanced equation for the reaction between them to get the stoichiometry and from that yo can see how many moles of dichromate react with moles of iron(II).

Have you studied redox?

yeah i just finished redox a few days ago. How would you know that this is a redox reaction? :0