Question

In the laboratory you dissolve 14.9 g of magnesium bromide in a volumetric flask and add water to a total volume of 375 mL. What is the molarity of the solution? M. What is the concentration of the magnesium cation? M. What is the concentration of the bromide anion? M.

Answer 1

Given mass of MgBr2 is 14.9 g and volume=375 ml=0.375 L.

We know that molar mass of MgBr2=184.113 g/mol.

Moles of MgBr2=mass/molar mass=14.9 g/184.113 g/mol=0.0809 moles.

Therefore Molarity of MgBr2=moles/Volume (L)=0.809 moles/0.375 L=0.2158 M.

The Molarity of MgBr2=0.2158 M.

In MgBr2, moles of Mg+2=moles of MgBr2 (or Molarity of MgBr2) and moles of Br-=2xmoles of MgBr2(or 2x Molarity of MgBr2)

So Molarity or concentration of Mg+2=0.2158 M, and concentration of Br-=2x0.2158=0.4316 M.