Question

1. 20 g of MgCO3 are dissolved in water and brought to a final volume of 700 mL. What is the molar concentration of the solution?

2. Calculate the normality of the solution.

3. If the MgCO3 completely dissociates to Mg2+ and CO3 2- , what are the concentrations of Mg2+ and CO3 2- (in g/L) in the solution?

4. Calculate the mass fraction of Mg2+ in the solution.

5. Calculate the molar fraction of C in solution.

Answer 1

1)

mass of MgCO3 = 20 g

molar mass of MgCO3 = 84.3 g / mol

moles of MgCO3 = mass / molar mass

                           = 20 / 84.3

                           = 0.237

volume = 700 mL = 0.700 L

molarity = moles / volume

              = 0.237 / 0.700

             = 0.339 M

molar concentration = 0.339 M

2)

normality = n x molarity

n = valency of cation or anion = 2

normality = 2 x 0.339

noramlity = 0.678 N

3)

Molarity Mg+2 = 0.339 mol / L

                        = 0.339 mol / L x 24 g / mol

                       = 8.14 g / L

CO3-2 = 0.339 mol / L

             =0.339 x 60

             = 20.3 g / L