1. Effect of Temperature
For some substances to dissolve in a given solvent, heat is absorbed. The reaction is endothermic. In this case, an increase in temperature increases solubility. For some substances, heat is released when they dissolve in a given solvent. The reaction is called exothermic. In this case, an increase in temperature decreases solubility. Generally, an increase in temperature in the solubility of solids in liquids increases solubility. But for solubility of gas in liquids, an increase in temperature decreases solubility because gas evaporates as temperature increases. . 2. Effect of Pressure
Pressure unlike temperature has little effect on solutions unless the solute is a gas. An increase in pressure causes greater interaction between particles of the gas and the liquid, thus, increasing solubility. 3. Nature of solute and solvent
Nature of both the solute and the solvent affect the solubility. •Substances with similar intermolecular attractive forces tend to be soluble in one another. This generalization is stated as "like dissolves like." •Non polar solutes are soluble in non polar solvents; Polar or ionic solutes are soluble in polar solvents •
Liquids that are attracted by charged objects are composed of polar molecules; those that are not attracted by a charged body are non polar Rate of Solubility
Sharon Barfield Perkins Bass
1140 W. 66th St.
Chicago IL 60621
This can be adapted for any grade. Discover factors affecting the rate of solution.
The materials are for each group of four.
1. Test tube with cork 9. Sugar cubes
2. Two clear plastic cups 10. Aspirin
3. Pestle 11. Salt tablets
4. Mortar 12. Mint candy
5. Clock with second hand or stopwatches 13. Water
6. Alcohol burner 14. Alka Seltzer
7. Goggles 15. Junior Mints
8. Mints 16. Tongs
1. Introduce and discuss solvent, soluble, solute, insoluble, and rate. 2. Demonstrate what the students will be expected to do using the vocabulary introduced.
3. Discuss safety and have groups get materials, including instruction sheet. 4. Fill containers with water as marked. Test tubes-room temperature; Cups-one room temperature, one cold.
5. One solute will be dropped into each solvent. Make a hypothesis about what will happen before adding the solutes.
6. Place one test tube over the flame, holding it with the tongs. Place the cork in the second tube and shake.
7. Use the mortar to crush the solute and put it in the cup containing room temperature water. Drop a solute into the cold solvent and let it sit. 8. Record the length of time needed to dissolve the solvents. If a solvent hasn't completely dissolved in 5 minutes write 5+ on your chart and discard all solvents.
9. Repeat steps 4 through 7 for the remaining solutes, except for the Junior Mints.
10. Pass out a new set of instructions and the Junior Mints. 11. Each student will place one Junior Mint in his/her mouth. 12. Do not move it around. Time how long it takes for it to dissolve. Write down every member's time.
13. Now put one in your mouth and move it around. How long did it take to dissolve? Write down the fastest time for the group.
14. The group members with the fastest time will compete against each other. 15. Put a Junior Mint in the mouth and move it around. The one who dissolves the mint first is the winner.
16. Discuss what took place. Discuss whether their hypotheses were correct. 17. Review vocabulary and factors that affect the rate of solubility. 18. Have the students act out what the molecules of the solute are doing when a solvent is being heated, when it is cold, when it is being shaken, and when it is just sitting at room temperature.
Given an unknown solute, determine which method used in the experiments will be fastest in dissolving the solute. The group dissolving it first will receive extra credit points....