1. The Solubility of Salts

2. The Meaning of Soluble
Strictly speaking, everything dissolves in water. Even glass dissolves in water. However, the amount that dissolves is so small that glass is said to have negligible solubility in water. Technically there is nothing that is insoluble, but we talk about substances with low solubility, referring to them as insoluble.

3. Low Solubility
When compounds dissolve slightly in water they are said to have low solubility. Lead II chloride (yellow solid) has low solubility in water (but enough is dissolved to give a person lead poisoning). An arbitrary value has been set for low solubility. If a substance has a solubility lower than 0.1 M, it has low solubility. Solubility < 0.1 M means low solubility.

4. Determining Compound Solubility
A Solubility Table of Ions is used to determine the solubility of ionic compounds. Determine the solubility of CaSO4 .

5. Using the Solubility Table
Determine the solubility of FeCO3 . First locate the compound’s negative ion (second in the formula) in the chart’s first column. Then locate the positive ion (first in the formula) in the chart’s second column. Then follow the row of this positive ion to the right column to read its solubility.

6. Precipitates
When two solutions are mixed, some ions may react to form solids called precipitates. These precipitates have low solubility. (These are called precipitates because they settle to the bottom of the container like rain precipitation falls to the ground).

7. Predicting Precipitates (Low Solubility Compounds)
Will a precipitate form when 100 mL of .20 M solutions of CaS and Na2SO4 are mixed? Note that in the mixing process the ions are diluted so that the ion concentrations of Ca2+ ,S2- and SO42- are .10 M ([Na+] is .20 M). To determine possible precipitates, consider only the cross products.
Ca2+
S 2-
2 Na+
SO42-

8. Does a Precipitate Form?
Ca2+
S 2-
2 Na+
SO42-
Na2S is soluble (top row)
CaSO4 is insoluble and settles out as a ppt.

9. Making Insoluble Salts From Solutions
You are required to make solid aluminum sulfite. You will need to use two solutions, each of which has one of these ions in a soluble form. Since all alkali metals are soluble with any anion, Na2SO4 would be soluble with its ions dissolved in solution. Likewise, since all nitrate compounds are soluble with any cation, Al(NO3)3 would be soluble too. When mixed, the Al3+ and SO42- ions would react to form insoluble Al2(SO4)3. Filtering would remove this insoluble compound.

10. Writing Formula Equations, Complete Ionic Equations and Net Ionic Equations

11. End of Presentation