Physical Science

Experiment 4-3

Background Information

We know that concentration is a characteristic property of a solution.

We have defined concentration as the mass of solute per 100 cm³ of solvent;  the units are g/100cm³

We have defined solubility as the limit of the maximum amount of a solute that will dissolve in a solute.  In Experiment 4-2 we determined a way to measure and communicate the solubility of a substance.

Experiment

Purpose:  In this experiment we shall see if change in temperature has any effect on solubility.

• table salt, (NaCl)
• a second solid to compare, perhaps table sugar, C₁₂H₂₂O₁₁. (Sugar is not ideal for this experiment.  A better substance would be a plant fertilizer with high nitrogen (N) content. But sugar should illustrate the effect.)
• cold water
• cold carbonated beverage
• three containers (such as test tubes) for gently heating several solutions simultaneously.
• heating device and container of water to warming several samples while maintaining same temperature for all.
• stir stick

Procedure:

1. Fill two containers about half full (perhaps 20cm³) of cold water.
2. In the first container stir in enough salt (perhaps a 10mL or a table spoon) to saturate the solution, leaving some excess salt undissolved.
3. In the second container stir in the same amount of sugar or other solid.  If excess does not remain, add more solid to each container.
4. Note and record the amount of undissolved solid in each container.  This might be roughly measured with a ruler as the height of the solid.
5. In the third container pour an equal amount of carbonated beverage.  In this solution we will be observing the dissolved gas, carbon dioxide (CO₂).
6. Place all three open containers in a container (pot?) of water and gently heat until the water boils.  Occasionally stir each container's contents.  CAUTIONS:  Steam contains much energy and can rapidly damage skin.  Be careful not to spill hot water potentially causing skin damage.
7. Observe any bubbles forced out of the solution during the heating of the beverage.  What does this indicate about the effect of temperature on the solubility of the gas?
8. Note and record any change in the amount of solid undissolved in the first two containers.  What does this indicate about the effect of temperature on the solubility of the solids?

Record your results in your science journal.  Write a Formal Report if you need to earn credit.

Discussion of Observations and Conclusion:  If MORE solid is in a container when hot, then the solubility must be less when hotter.  If there is LESS solid is in a container when hot, then the solubility must be more when hotter.  It is generally not wise to taste substances used for experimentation, but you might recall that carbonated beverages left open and warm for a period of time also taste flat.  This is also an indication of the effect of temperature on the solubility of CO₂.

The temperature effects on the solubilities of other gases are similar.  When rivers and lakes are warmer, because the solubility of oxygen (O₂) is reduced, there generally is less oxygen available for fish and other aquatic animals.

The effect of temperature effects on the solubilities is not as uniform.  Most solids are more soluble at higher temperature, but a few are less soluble.  The difference in the effects of higher temperature on solubilities can sometimes be used to separate solids.

Additional Experiment

Devise a procedure and use it to separate a mixture of two solids for which temperature has different effects on solubility.