http://www.ck12.org Chapter 10. Chemistry of Solutions
FIGURE 10.2
This graph shows the amount of different
solids that can dissolve in 1 L of water at
20 degrees C.Saturation
There is a limit on the amount of solute that can dissolve in a given solvent. Tanya found this out with her baking
soda mixture. But even sugar, which is very soluble, has an upper limit. The maximum amount of table sugar that
will dissolve in 1 L of water at 20°C is about 2000 g. If you add more sugar than this, the extra sugar won’t dissolve.
A solution that contains as much solute as can dissolve at a given temperature is called asaturated solution. A
solution that contains less solute than can dissolve at a given temperature is called anunsaturated solution. A
solution of 2000 grams of sugar in 1 L of 20°C water is saturated. That’s all the sugar the solution can hold. Any
solution containing less than 2000 g of sugar is unsaturated. It can hold more sugar. To learn more about saturated
and unsaturated solutions, watch the video at this URL: http://www.youtube.com/watch?v=IKimraU21ws.
You Try It!
Problem: A solution contains 249 grams of Epsom salt in 1 L of water at 20°C. Is the solution saturated or
unsaturated?
Problem:Give an example of an unsaturated solution of table salt in 1 L of 20°C water.
Factors That Affect Solubility
Certain factors can change the solubility of a solute. Temperature is one such factor. How temperature affects
solubility depends on the state of the solute, as you can see inFigure10.3.
- If a solute is a solid or liquid, increasing the temperature increases its solubility. For example, more sugar can
dissolve in hot tea than in iced tea. - If a solute is a gas, increasing the temperature decreases its solubility. For example, less carbon dioxide can
dissolve in warm ocean water than in cold ocean water.
The solubility of gases is also affected by pressure. Pressure is the amount of force pushing against a given area.
Increasing the pressure on a gas increases its solubility. Did you ever open a can of soda and notice how it fizzes out
of the can? Soda contains carbon dioxide. Opening the can reduces the pressure on the gas so it is less soluble. As a
result, some of the carbon dioxide comes out of solution and rushes into the air.