Applications of Solubility

1

• Applications of Solubility

1.
Chloride Ion Titration

• The concentration of chloride ion in a water
  sample is determined.
• Adding Ag to the water sample will cause AgCl(s)
  to precipitate

Ag(aq) Cl-(aq) ? AgCl(s)

• Enough Ag is added to react with all of the Cl-
• The moles of Ag added equal the moles of Cl-
  that were present in the water sample and Cl-
  can be calculated.

2
eg
25.0mL of a water sample was titrated with 0.500M
AgNO3(aq), using sodium chromate as an indicator.
At the equivalence point 26.8mL of AgNO3
solution had been added. What was the Cl- in
the water sample?

• Moles of AgNO3 used

Ag(aq) Cl-(aq) ? AgCl(s)

• moles of Cl- moles of AgNO3 used

3
2.
Softening Hard Water

• Hard water is caused by the presence of metal
  ions such as Ca2 and Mg2
• These ions react with soap molecules and inhibit
  their function.
• Slow-moving ground water (such as well water) is
  most likely to be hard (more time for ions to
  dissolve into the water).
• To soften water, washing soda may be added
  (Na2CO3)
• The washing soda precipitates the metal ions

Ca2(aq) CO32-(aq) ? CaCO3(s)
Mg2(aq) CO32-(aq) ? MgCO3(s)