1. Solutions, Acids, and Bases Section 2 Dissolving and Solubility
PHYSICAL SCIENCE
Solutions, Acids, and Bases
Section 2 Dissolving and Solubility

2. Dissolving and Solubility Objectives
Describe how a substance dissolves in terms of its solubility, molecular motion, and solute-solvent interactions.
Identify several factors that affect the rate at which a substance dissolves.
Relate the structure of water to its ability to dissolve many different substances.
Distinguish between saturated, unsaturated, and supersaturated solutions.

3. The Process of Dissolving
Solutions with a larger surface area dissolve faster.
A given volume of solute will dissolve much faster if it is in smaller pieces as opposed to larger pieces
When a solid is whole, most molecules are buried within it
The broken (or crushed) solid has more surface area which leads to more solute-solvent collisions – hence it dissolves quicker

4. Surface Area & Solubility

5. The Process of Dissolving
Stirring or shaking a solution helps the solute dissolve faster.
A solute can diffuse (spread out) in a solution
Stirring or shaking the solution moves the dissolved solute away from the portion of the solute that has not come into contact with the solvent

6. The Process of Dissolving
Solutes dissolve faster when the solvent is hot.
Solutes dissolve faster in hot water than they do in cold water
If a substance is heated, its particles move faster, creating the potential for more collisions between particles
The collisions between particles also transfer energy

7. Heat and Stirring
Heating and stirring a solution can increase the solubility of solutes in solvents.
Instruments can be purchased that do both in the lab to allow for solutions to be prepared.

8. The Process of Dissolving
Not every substance dissolves.
Substances that dissolve in a solvent are said to be soluble in that solvent
Substances that do not dissolve in a particular solvent are said to be insoluble in that solvent
It is also possible for substances to be only partly soluble in a solvent

9. Water: A Common Solvent
Water is sometimes called the universal solvent because so many substances can dissolve in water.
Water molecules are polar because the oxygen atom attracts the shared electrons more strongly than the hydrogen atoms in a water molecule.
The result is a polarized molecule in which the oxygen atom has a partial negative charge and the hydrogen atoms have a partial positive charge.

10. Water: A Common Solvent
The lower case Greek letter delta () is used to show that a charge is partial.
The polarity of water molecules is the key to hydrogen bonding which influences many of the characteristics that we observe in water.

11. Water: A Common Solvent
Substances made of molecules that dissolve in water also have partial charges that interact with water molecules.
Like dissolves like means that non-polar solutes can be dissolved in non-polar solvents and polar solutes can be dissolved in polar solvents.

12. Concentration
Concentration is the quantity of solute dissolved in a given quantity of solution.
If a small quantity of solute is dissolved in a large volume of solvent, the resulting solution is said to be dilute
A concentrated solution has a large quantity of dissolved solute
An unsaturated solution is a solution that is able to dissolve more solute.

13. Concentration
A saturated solution is a solution that cannot dissolve any more solute at the given conditions.
A saturated solution is in equilibrium
A saturated solution contains the greatest quantity of solute that will dissolve in a given quantity of solvent at a particular temperature
Solubility is the greatest quantity of a solute that will dissolve in a given quantity of solvent to produce a saturated solution.

14. Concentration
Heating a saturated solution allows you to dissolve even more solute.
The solubility of many solutes increases as the temperature of the solution increases
A supersaturated solution is a solution holding more dissolved solute than is specified by its solubility at a given temperature
A supersaturated solution is created by heating a solution and adding more solute than specified by its solubility at a lower temperature, then dropping the temperature of the solution

15. Concentration
Heating a saturated solution allows you to dissolve even more solute. Cont’d
Adding a small crystal of solute to a supersaturated solution usually results in the excess solute crystallizing out of the solution until the solution is once again saturated at the lower temperature

16. Concentration
Measuring concentration precisely can be done a couple of ways.
One can express a solution as grams of solute per 100 g of solvent
Concentration can also be expressed as a mass percent, or grams of solute per 100 g of solution
Concentration may be expressed in units of molarity
Molarity = moles of solute/liters of solution or M=mol/L
For example, a 1.0 M (one molar) solution of sodium chloride contains 1.0 mol of dissolved NaCl for every 1.0 L or solution