Percentage calculation of chromium compound

[Paulo2014]

Homework Statement

20g of Cr2(SO4)3 was used to make up an 800 ml batch of tanning liquor. When the tanning process was complete, a 10ml sample was taken and the chromium remaining in the sample was determined.
The chromium in the sample was oxidised to dichromate and then titrated with a 0.100molL solution of iron 2 ions.
Given that 16.5ml of the iron solution was needed, determine the percentage of the chromium used up in the tanning process

Homework Equations

The Attempt at a Solution

I am unsure as to how to get an answer, I get the number of moles of Cr3+ used in tanning but I don't know how to get a percentage of chromium.

 

[Borek]

What is percentage definition?

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[Blueshift5]

Can you provide more information about the experiment and the desired outcome? Are you trying to calculate the efficiency of the tanning process, or the amount of chromium remaining in the tanning liquor after the process? Also, what is the concentration of the chromium in the tanning liquor? More information is needed to accurately calculate the percentage of chromium used in the tanning process.