
To calculate
The molality of each of the given seawater ions from given molarity and density.

Answer to Problem 11.40QA
Solution
a) Molality of Na+ = 0.474 m
b) Molality of K+ = 1.02 x 10-2 m
c) Molality of Mg2+ = 5.29 x 10-2 m
d) Molality of Ca2+ = 1.03 x 10-2 m
e) Molality of Sr2+ = 9.05 x 10-5 m
f) Molality of Cl- = 0.557 m
g) Molality of SO42- = 2.83 x 10-2 m
h) Molality of HCO3- = 2.06 x 10-3 m
i) Molality of Br - = 8.44 x 10-4 m
j) Molality of B(OH)3 = 4.16 x 10-4 m
k) Molality of F - = 6.83 x 10-5 m
Explanation of Solution
Molality of the solution is moles of solute divided by the mass of solvent in kg.
Molarity of the solution is moles of solute divide by L of solution.
Density of solution is mass divided by volume of solution
Mass of the solution is mass of solvent and mass of solute
To calculate the molality of the ions, we need to calculate the moles of solute and mass of solvent in kg from the given density and molarity.
a) Calculation of molality of Na+
Given
Calculations
To calculate the moles of Na+ from
So moles of solute
The mass of Na+ is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of Na+ and mass of solution; we can calculate the mass of solvent.
The molality of the Na+ ion in sea water from the moles and mass of solvent is
The molality of the Na+ ion in sea water is
b) Calculation of molality of K+
Given
Calculations
To calculate the moles of K+ from
So moles of solute =
The mass of K+ is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of K+ and mass of solution; we can calculate the mass of solvent.
The molality of the K+ ions from the moles and mass of solvent is
The molality of the K+ ion is
c) Calculation of molality of Mg2+
Given
Calculations
To calculate the moles of Mg2+ from
So moles of solute
The mass of Mg2+ is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of Mg2+ and mass of solution; we can calculate the mass of solvent.
The molality of the Mg2+ ions from the moles and mass of solvent is
The molality of the Mg2+ ion is
d) Calculation of molality of Ca2+
Given
Calculations
To calculate the moles of Ca2+ from
So moles of solute
The mass of Ca2+ is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of Ca2+ and mass of solution; we can calculate the mass of solvent.
The molality of the Ca2+ ions from the moles and mass of solvent is
The molality of the Ca2+ ion is
e) Calculation of molality of Sr2+
Given
Calculations
To calculate the moles of Sr2+ from
So moles of solute = 0.0000928 mol Sr2+
The mass of Sr2+ is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of Sr2+ and mass of solution; we can calculate the mass of solvent.
The molality of the Sr2+ ions from the moles and mass of solvent is
The molality of the Sr2+ ion is
f) Calculation of molality of Cl-
Given
Calculations
To calculate the moles of Cl- from
So moles of solute
The mass of Cl- is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of Cl- and mass of solution; we can calculate the mass of solvent.
The molality of the Cl- ions from the moles and mass of solvent is
The molality of the Cl- ion is
g) Calculation of molality of SO42-
Given
Calculations
To calculate the moles of SO42- from
So moles of solute
The mass of SO42- is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of SO42- and mass of solution; we can calculate the mass of solvent.
The molality of the SO42- ions from the moles and mass of solvent is
The molality of the SO42- ion is
h) Calculation of molality of HCO3-
Given
Calculations
To calculate the moles of HCO3- from
So moles of solute
The mass of HCO3- is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of HCO3- and mass of solution; we can calculate the mass of solvent.
The molality of the HCO3- ions from the moles and mass of solvent is
The molality of the HCO3- ion is
i) Calculation of molality of Br-
Given
Calculations
To calculate the moles of Br- from
So moles of solute
The mass of Br- is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of Br- and mass of solution; we can calculate the mass of solvent.
The molality of the Br- ions from the moles and mass of solvent is
The molality of the Br- ion is
j) Calculation of molality of B(OH)3
Given
Calculations
To calculate the moles of
So moles of solute
The mass of
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of
The molality of the
The molality of the
i) Calculation of molality of F-
Given
Calculations
To calculate the moles of F- from
So moles of solute
The mass of F- is
The density of the solution in g/mL is
So 1 L of the solution contains
We know the mass of Br- and mass of solution; we can calculate the mass of solvent.
The molality of the F- ions from the moles and mass of solvent is
The molality of the F- ion is
Conclusion
Molarity of the major ions present sea water has been calculated from the molarity and density.
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Chapter 11 Solutions
Chemistry: An Atoms-Focused Approach
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