[dgolverk]

Hi,
As part of my experiment I need to find a way to precipitate arsenic (arsenate ion AsO4-3) using:
i) Iron(iii) sulfate
ii) Calcium hydroxide
3Ca(OH) + 2AsO4 => Ca3(AsO4)2 + 3OH is that right?
What my equations will look like for case i) and ii)?
I already calculated the amount of arsenic in a liter of water (0.004mol/L), but I'm struggling with creating and equation that shows the reaction between the arsenate ion and the coagulants. I only need the equations, I will balance them myself.

Thank you very much,

[Borek]

What is formula of arsenic acid?

Are you going to preciptate AsO₄^3- from the solution of arsenic acid, or some salt, like Na₃AsO₄?

[dgolverk]

I just need to precipitate arsenic in any form...
I just need to write a simple equation, something like that 3Ca(OH) + 2AsO4 => Ca3(AsO4)2 + 3OH, if that's right.

[Borek]

Don't ignore charges in your equations, you are dealing with ions. What you wrote can be OK, once you will balance charge and add state of matter information.