[bromobutane]

to confirm the presence of Fe3+ ion, 2 drops of sodium hydroxide is added after the potassium thiocyanate solution. What would be different about the solution after the addition of sodium hydroxide? (Ignore any possible reaction between NaOH and either Fe3+ or the potassium thiocyanate.

Also after sodium hydroxide is added, the procedure calls to add 4 drops of nitric acid. What does the nitric acid do? (again, the problem tells you to ignore the reaction between HNO3 and Fe3+ or SCN-)

Finally why is the nitric acid added twice as much as NaOH?

Thanks in advance!

[Borek]

What would be different about the solution

What solution? How do you expect us to know to what the NaOH was added?

[bromobutane]

so the NaOh is added to a solution of Fe3+ and potassium thiocyanate.

[Borek]

Is that everything that is present in the solution?

Question is quite general, so it is hard to guess what is the intended answer. But there is definitely a property of water solutions that change when you add bases (or acids).

[pcm81]

https://en.wikipedia.org/wiki/Potassium_thiocyanate

Dilute aqueous KSCN is occasionally used for moderately realistic blood effects in film and theater. It can be painted onto a surface or kept as a colorless solution. When in contact with ferric chloride solution (or other solutions containing Fe3+), the product of the reaction is a solution with a blood red colour, due to the formation of the thiocyanatoiron complex ion. Thus this chemical is often used to create the effect of 'stigmata'. Because both solutions are colorless, they can be placed separately on each hand. When the hands are brought into contact, the solutions react and the effect looks remarkably like stigmata.[citation needed]

Similarly, this reaction is used as a test for Fe3+ in the laboratory.

I wonder if raising pH with NaOH nullifies the effect?
Kind of like adding H2SO4 as proton donor for KMnO4 test for Iron.