1. “Composition VII”, Wassily Kandinsky,
Ionic Solvation
Vocabulary:
polyatomic ion
dissociation
solubility chart
electricity
electrolyte
nonelectrolyte
soluble
insoluble
aqueous
non-aqueous
“Composition VII”, Wassily Kandinsky,
Russian, 1913

2. Watch

3. Why do some of the substances dissolved in water conduct electricity and some do not?

4. Dissociation
When an ionic compound like sodium chloride dissolves in water, the ions dissociate. Take a look:

5. Dissociation
The ions are more attracted to the water molecules than they are to each other.

6. Electricity
Only solutions that have dissociated ions in them can conduct electricity because electricity is the movement of charges. If there are no charges that can move then there is no electricity. Substances that form ions in solution and conduct electricity are called electrolytes.

7. So what does this look like at the particle level with something soluble, like Cu(NO3)2?
Notice that the ions are separate from one another and are free to move around in the solution. Also, notice there are twice as many NO3- ions as Cu2+ ions and that the total charge is zero.
NO3-
Cu2+
NO3-
NO3-
NO3-
Cu2+
Cu2+
NO3-
NO3-

8. But wait!
If you go back to slide 2 and watch the original video again, you’ll see that some ionic compounds in water like BaSO4 do not conduct electricity. Why not? Think about it!

9. Solubility
Not all ionic compounds dissociate in water! These are called nonelectrolytes. The ions in the solid are more attracted to themselves than they are to the water molecules.

10. So what does this look like at the particle level with something insoluble, like PbI2?
Notice that the ions are bonded as a solid and are not free to move around in the solution. Also, notice there are twice as many I- ions as Pb2+ ions and that the total charge is zero. I- I- I-
Pb2+
Pb2+
Pb2+ I- I- I-

11. Solubility
So how do you know if an ionic compound dissolves or doesn’t dissolve?

12. Solubility Chart
You were given a chart that tells you! It’s called a solubility chart which summarizes the rules about which substances generally dissolve and which do not.
Get out the periodic table you were given on the first day of school, or borrow one of mine.

13. Solubility Chart
Dissolves in water = soluble = aqueous Doesn’t dissolve in water = insoluble = solid

14. Polyatomic Ions
You’ll notice that some of the ions are a little more complicated such as NO3-.
These are called polyatomic ions and are found on the polyatomic ion sheet on the same page as the solubility chart.
Polyatomic ions are groups of ions that act as one particle with an overall charge.

15. Practice
Determine if each of the following is soluble or insoluble. Notice that the negative ion is always listed second in the formula and the positive ion is always listed first.
AgCl
Cu(NO3)2
K2SO4
(NH4)3PO4
PbI2

16. 1. AgCl
Step 1: Find the negative ion. Step 2: Find the positive ion. Step 3: Determine if the compound is soluble (aqueous, aq) or insoluble (solid, s) So AgCl is insoluble. It will not dissolve in water.

17. 2. Cu(NO3)2 Step 1: Find the negative ion.
Step 2: Find the positive ion.
Step 3: Determine if the compound is soluble (aqueous, aq) or insoluble (solid, s)
So Cu(NO3)2 is soluble. It will dissolve in water.

18. 3. K2SO4 Step 1: Find the negative ion. Step 2: Find the positive ion.
Step 3: Determine if the compound is soluble (aqueous, aq) or insoluble (solid, s)
So K2SO4 is soluble. It will dissolve in water.

19. More practice Is (NH3)3PO4 soluble or insoluble?
Is PbI2 soluble or insoluble?
Insoluble
Is Na2CO3 soluble or insoluble?
Soluble (remember, sodium is an alkali metal!)