Lecture 4.2 – The Dissolving Process and the Rate of Dissolving

A Problem

Cools down to room

temperature

Gross!

Justify – TPS• Why does this solid appear at cold

temperatures, but it wasnt present when the cider was hot?

How does temperature, pressure, and surface area impact rate of dissolving?

I. Dissolving• We can alter the rate at which the solute

dissolves by:1. Changing the temperature2. Changing the surface area of the

solute3. Changing the pressure of the

solution.

II. Temperature and Dissolving• As you increase the

temperature, molecules start moving faster.

• By moving faster, the molecules are better able to grab the solute, form the cages around them and pull them into the solution.

• Therefore, the faster molecules are moving, the faster something dissolves.

Remember What Dissolving Looks Like?

Temperature and Dissolving Rate

Cold liquid Hot liquid

III. Surface Area and Dissolving

• As you increase the surface area, the rate at which the solute dissolves increases.

• As you increase the surface area of a substance, you are providing more sites for the solvent to interact with the solute.

Surface Area and Dissolving

Making a Carbonated Beverage

Justify – TPS

• Why does your soda become carbonated when you open it? What is happening?

IV. Pressure and Dissolving• As you increase the pressure, the rate at

which the solute dissolves increases.• The solubility and pressure relationship is

clearly seen when a gas dissolves in a liquid. • Gases can dissolve into liquids.

IV. Pressure and Dissolving• When a gas is above a liquid and the pressure

is increased, the gas molecules collide more often with the wall of the liquid and this causes more gas to be pushed into the liquid.

SUMMARIZE