Chemistry: Solving limiting reactant problems in solution

Question

Suppose 0.206g of iron(II) bromide is dissolved in 100.mL of a 11.0mM aqueous solution of silver nitrate. Calculate the final molarity of bromide anion in the solution. You can assume the volume of the solution doesn't change when the iron(II) bromide is dissolved in it. Be sure your answer has the correct number of significant digits. 

Answer 1

Write the correctly balanced equation:

FeBr₂(aq) + 2AgNO₃(aq) ==> Fe(NO₃)₂(aq) + 2AgBr(s)

Find limiting reactant by seeing how much AgBr(s) is formed from each:

For FeBr₂: 0.206 g x 1 mole/215.7 g x 2 mole AgBr/1 mole FeBr₂ = 0.00191 moles

For AgNO₃: 100. ml x 1 L/1000 ml x 11.0 mol/L x 2 mol AgBr/2 mol AgNO₃ = 1.10 moles

So, FeBr₂ is limiting

Since AgBr is insoluble, there will be no, or very little bromide anion left in solution. It will all be precipitated in the form of AgBr. If you want to find the "actual" concentration of Br- in solution, you need the Ksp value for AgBr.