The Concentration of Ions in Solution
The solutions we work with in chemistry often involve ionic compounds and acids. Both of these
produce electrolytic solutions, meaning they conduct an electrical current due to the production
of ions in solution.
It will often be important for us to be able to determine the concentration of these ions, not
just the overall concentration of the solution.
For example:
1) Write the balanced reaction equation that will show the ions produced when sodium
carbonate, dissociates into ions as it dissolves in water.
Na2CO3 (s) → 2 Na+(aq) + CO32-(aq)
2) If we have a 0.20 M solution of Na2CO3 , what will be the concentration of our two ions,
Na+and CO32-?
3) Calculate ion concentrations in a 2.00 L solution containing 10.1 g ammonium sulfate.
PRACTICE:
1.
Write balanced reaction equation that show which ions are produced when the following substances are
dissolved in water.
a. lithium hydroxide ________________________________________________________________
b. potassium phosphate _____________________________________________________________
c.
strontium chloride _______________________________________________________________
d. chromium(III) sulfate ____________________________________________________________
2. Iron(III) nitrate has a solubility of 0.15 M. Find concentration of the ions in solution.
3. Calculate ion concentrations in a 2.00 L solution containing 17.1 g aluminum sulfate, Al 2(SO4)3
SOLVATION OF SODIUM CHLORIDE
cations are positively charged
(also known as HYDRATION)
anions are negatively charged
Closer view:
Description of the Solvation (or Hydration) Process:
H2O is a polar molecule. These charged regions are
attracted to ions with the opposite charge. Hence, the
positively charged regions of water molecules are
attracted to Cl- ions, and the negatively charged regions
of water molecules are attracted to Na+ ions. When
several water molecules surround an ion in the crystal,
the sum of the attractive forces between the water
molecules and the ion may become strong enough to
overcome the attractive forces between the cations and
anions in the crystal. The water molecules form a shell
of solvation around the ion, and the water-surrounded
ion can break away from the crystal