[horizontm]

"a water sample is suspected to be contaminated by iron (III) ions. How could you determine if the sample is really contaminated? If the sample is found to be contaminated, how could you measure the concentration of iron (III) in the sample?"

I am not asking for answers, but rather where do I start in my research for this answer? Thanks.

[english]

Perhaps a salt that contains an anion that, when combined with Fe³⁺, gives a notable color change to the solution.