[oliver_bagay]

Why do we use KI, 20% H2SO4, and starch? Why can't we use HCl instead of H2SO4? What happens when we add more KI and starch other than what is required.

[Hunter2]

Look what does Chromic acid do with HCl. Chlorine is a halogen like iodine.

[Arkcon]

What happens when we add more KI and starch other than what is required.

Hunter2: has already asked you about the first one.  Now lets work with this one.  What you have to ask yourself (if you want to learn) is what is an indicator, and how does it work?  By definition (in at least this case,) it undergoes a reaction with excess titrant, to let you you've added enough.  So what would happen if there's excess?

I hope you don't mind us answering your questions with more questions, but that's what we do here.  Its all in the Forum Rules{click}, we want to see your attempt, so please click on that link, read the contents, and comply with our rules, so we can help you.