Unit 1 – Day 12

1. Unit 1 – Day 12 Solubility Rules

2. Solubility • When discussing ionic and covalent compounds we learned that ionic compounds are soluble in water. • This is not always true however. Many ionic compounds are insoluble. • This depends on both the positive (cation) and negative (anion) in the compound.

3. Why care? • Creating insoluble compounds can create many problems at home or at work. • One example is hard water. • Hard water is not toxic or harmful, but it can be inconvenient. • The water contains dissolved ions of calcium, iron and magnesium. • These ions react with soap to form soap scum, an insoluble precipitate.

5. Scaling • Hard water in a kettle or coffee maker can cause calcium carbonate to build up as scale deposits. • It can impede the flow of water in hot water tanks.

6. Solubility Rules • We will be using a table of rules to determine if a compound is soluble or not. • For example, lead (IV) chloride is soluble, while lead (II) chloride is not.

7. Some rules that are always true • All NITRATES are always soluble. • All ACETATES are always soluble. • All Alkali metal compounds (Li+, Na+, K+ etc) are always soluble. • All ammonium (NH4+) compounds are always soluble. • For these, and all other compounds, you can always look on the chart.

8. Examples • Try and determine if the following compounds are soluble: • Iron (III) carbonate • Calcium hydroxide • Sodium phosphate • Aluminum nitrate • Barium sulphate No No Yes Yes No

9. When two solutions mix… • When we mix two solutions, there is a double displacement reaction. • The compounds can switch ions. • If one of these combinations is insoluble, it will form as a solid precipitate.

10. Examples • Copper (II) chloride and Potassium Carbonate are mixed. Will a precipitate form? • CuCl2 + K2CO3 KCl + CuCO3 • Check the solubility of both products. • CuCO3 is insoluble, and will form a precipitate. • Try it again for copper (II) nitrate and lead (II) acetate. Will a precipitate form if they mix?