1. Saturation & Solubility
Is there a limit to how much sugar you can dissolve in a cup of tea?

2. Saturation
saturated – a solution that contains as much solute as can possibly be dissolved under the existing conditions of temperature and pressure
unsaturated - a solution with less than the maximum amount of solute (it could hold more)
supersaturated – a solution that contains a greater amount of solute than that needed to form a saturated solution (this is an unstable situation; such a solution will not remain supersaturated for long)

3. Supersaturation Demo
If I dissolved 33g of NaCH3COO in 30g of water, calculate how many grams that would be in 100g of water. (think proportions)

4. Sketch this graph and locate the point you just calculated (x amount of NaCH3COO in 100g of water) at 75°C.
What adjective would you use to describe this solution at 75°C?
If the solution were cooled to 25°C (and nothing crystallized), how would you describe the solution?

5. Supersaturation Demo What does the flask look like to start with?
What happened over time as it sat still?
What did I add?
Then what happened? What does it look like now?
How would you describe the remaining solution after this change?

6. Solubility
Solubility is the amount of a solute that will dissolve in a specific solvent under given conditions.
determined experimentally
expressed in grams of solute per 100 grams of solvent (at a specific T and P)

7. Solubility
On a graph showing solubility versus temperature, (see Table D in your Reference Tables)
The line represents saturation for a particular substance at different temperatures.
A point above the line represents supersaturation (AS LONG AS ALL OF THE SOLUTE IS DISSOLVED),
while, a point below the line indicates an unsaturated solution.

8. Find the potassium nitrate (KNO3) curve on Table D

9. How many grams of KNO3 will dissolve in 100g of water at 50°C?
Approximately 83 grams of KNO3 will dissolve in 100 g of water at 50˚C

10. If you only put 70g of KNO3 in the water at 50°C, how would you describe the solution?
70g of KNO3 at 50 ˚C is below the line…therefore the solution is unsaturated
If about 83 grams can dissolve at 50 degrees, with only 70 dissolved, you should be able to dissolve about 13 more grams.

11. It is HARD to make a supersaturated solution
It is HARD to make a supersaturated solution. You would be lucky to get 70g of KNO3 to dissolve at 40°C.
How much would you expect to dissolve at 40˚C?
Probably about 63g.
If you put 70g potassium nitrate in 100g of water at 40˚C, how much solid would you expect to have on the bottom?
Probably about 7g.

12. Solubility is affected by:
temperature
how temperature affects solubility of a solid depends on if the dissolving process was endothermic or exothermic:
endothermic when dissolving – higher temperature results in increased solubility
exothermic when dissolving – higher temperature results in decreased solubility
gaseous solutes are less soluble at higher temperatures
increased kinetic energy of the solute (gas) increases the tendency for the gas to escape from the solvent

13. Solubility is affected by:
the nature of the solute and solvent
“like dissolves like” –
polar and ionic solutes dissolve in polar solvents but not in nonpolar solvents;
nonpolar solutes dissolve in nonpolar solvents but not in polar solvents (ex.: nonpolar oil molecules stay separated from polar water molecules in salad dressing)

14. Solubility is affected by:
pressure
solutions of solids and liquids not affected much by pressure
gas solubility is strongly affected by pressure
increased pressure increases the rate at which gas molecules strike the surface of solute
Henry’s Law: the solubility of a gas is proportional to the partial pressure of the gas above the liquid

15. Dissolving rate is affected by:
surface area – because solvent particles pull solute particles from the surface of the solute
stirring – because dissolved solute builds up next to the solid solute causing the dissolving process to slow down
temperature – solvent particles move faster at higher temperatures, so more solvent particles come into contact with the solid solute in a shorter period of time