2. Chemistry 20

3.  The solubility of a solute is the maximum quantity of solute that dissolves in a given quantity of solvent, at a given temperature.  For example, the solubility of sodium chloride, NaCl (s), in water at 20 o C is 36 g/100 mL.

4.  A saturated solution is a solution that contains the maximum amount of dissolved solute at a given temperature in the presence of undissolved solute.  For example, 100 mL of saturated NaCl (aq) would contain 36 g of dissolved NaCl at 20 o C. If more sodium chloride is added to the solution, it will not dissolve.

5.  An unsaturated solution is not saturated and, therefore, can dissolve more solute at that particular temperature.  For example, a solution containing 20 g of dissolved NaCl in 100 mL of water at 20 o C is unsaturated. This solution has the potential to dissolve an additional 16 g of NaCl before it becomes saturated.

6.  A supersaturated solution is a solution that contains more dissolved solute than its solubility at a given temperature.  For example, a solution containing 37 g of dissolved NaCl in 100 mL of water at 20 o C is supersaturated. Supersaturated solutions are never very stable and eventually the additional dissolved solute may crystallize.

7.  What mass of NaCl would be dissolved in 275 mL of saturated solution at 20 o C?  What volume of saturated solution would contain 5.52 g of dissolved NaCl at 20 o C?  A solution contains 21.4 g of dissolved NaCl in 150 mL of water at 20 o C. How much more NaCl could be dissolved into the water before it becomes saturated?

8.  What mass of NaCl would be dissolved in 275 mL of saturated solution at 20 o C? › 99 grams  What volume of saturated solution would contain 5.52 g of dissolved NaCl at 20 o C? › 15.3 mL  A solution contains 21.4 g of dissolved NaCl in 150 mL of water at 20 o C. How much more NaCl could be dissolved into the water before it becomes saturated? › 32.6 grams

9.  As an ionic compound is dissolved, it dissociates into the individual cations and anions.  For example, the dissociation of CuSO 4(s) can be shown as:  CuSO 4(s) in water Cu 2+ (aq) + SO 4 2- (aq)

10.  Crystallization is the reverse of dissolving and can be written as an equation such as: Cu 2+ (aq) + SO 4 2- (aq) in water CuSO 4(s)  In a saturated solution, which contains both dissolved and undissolved solute, both of these processes take place at the same time. in water  CuSO 4(s) Cu 2+ (aq) + SO 4 2- (aq)

11.  A saturated solution is considered to be in a state of equilibrium. Equilibrium occurs when two opposing processes take place at the same rate in a closed system.

12.  The solubility of a substance can vary greatly at different temperatures.  When a solid dissolves in a liquid, energy is needed to break the bonds holding the solid together. At higher temperatures, the particles of the solute and solvent have more energy.

13. In general, solids have a greater solubility at higher temperatures.  The bonds between particles in a liquid are not as strong as the bonds between particles in a solid. When a liquid dissolves in a liquid, additional energy is not needed.

14. In general, the solubility of liquids is not greatly affected by changes in temperature.  Gas particles move quickly and have a great deal of kinetic energy.  When a gas is dissolved in a liquid, the gas particles lose some of their energy. At higher temperatures, the dissolved gas gains energy again. As a result, the gas comes out of solution and is less soluble.

15.  In general, the solubility of gases decreases at higher temperatures.  The effect of temperature on solubility is illustrated by the problem of thermal pollution (industries releasing hot water into rivers/streams).

16.  As the temperature of the rivers/streams increase: › the dissolved oxygen comes out of the water and returns back into the atmosphere – fish and other aquatic wildlife may not have enough oxygen to breathe › harmful solutes such as mercury compounds and pesticides may become more soluble in the river/stream

17.  Pressure changes have very little effect on the solubility of liquids and solids.  Pressure changes do have a significant effect on the solubility of a gas in a liquid solvent.  The solubility of a gas is directly proportional to the partial pressure of that gas above the liquid.

18.  The solubility of oxygen in lake water depends on the partial pressure of the oxygen in the air above the lake.  If the pressure is suddenly decreased (such as when the lid of a carbonated drink is opened), the solubility of the gas will decrease, causing the gas to “bubble” out of the solution.

19.  Say I wanted to increase the amount of carbon dioxide dissolved in my pop. What are two strategies I could use to dissolve more?  Solubility practice questions