# How to calculate the concentration of a K₂Cr₂O₇ solution?

How many ml of acidified $\ce{K2Cr2O7}$ solution, which includes 21.6 g of dichromate ions per Litre, are required for the oxidation of 44.4 g of $\ce{CH3CH2CH(OH)CH3}$?

Obviously 44.4 g of $\ce{CH3CH2CH(OH)CH3}$ means 0.6 moles. So from the stoichiometry of the the oxidation we find out that 0.2 moles of $\ce{K2Cr2O7}$ are needed. I have trouble finding the concentration of $\ce{K2Cr2O7}$ though and thats why I need help.

To calculate the dichromate concentration (in moles/l) of the solution, simply divide the given mass of dichromate per litre (21,6 g) by the molar mass of $\ce{Cr2O7^{2-}}$.