Question

how to do stoichiometry someone please explain

Answer 1

First you need to correctly balance the chemical equation:  

3FeBr2 + 2K3(PO4)2 ------ Fe3(PO4)2 + 6KBr  

This is a double replacement reaction in which the positive ions trade places to produce two new compounds. The charge of each ion is as follows:  

Fe +2  

Br -1  

K +1  

PO4 -3  

Chemical formulas are balanced and then the chemical equation.  

From there you are doing a mass-mass stoichiometry problem.  

1. Take the mass of the iron (II) phosphate given divided by the molar mass of iron(II) phosphate from the periodic table.  

2. Multiply by the mole ratio of iron (II) bromide / iron (II) phosphate from your balanced equation  

3. Multiply by the molar mass of iron (II) bromide.  

1. 17.1 g Fe3(PO4)2 / 357.49 g/mol Fe3(PO4)2 = .048 moles  

2. .048 moles Fe3(PO4)2 X 3FeBr2 / Fe3(PO4)2 = . 144 moles FeBr2  

3. .144 moles FeBr2 X 215.65 g/mole FeBr2 = 31.1 g FeBr2