Justify TPSWhy do some things dissolve in water, but other things do not?

Lecture 4.2 The Dissolving Process and the Rate of Dissolving

Todays Learning TargetsLT 4.1 I can discuss how ionic solids dissolve due to the random molecular motion of the water molecules. LT 4.3 I can compare and contrast various intermolecular forces and relate them to the dissolving process of a solid. LT 4.4 I can hypothesize how surface area, temperature, and pressure impact the dissolving process of a solid.

Why do substances dissolve?

I. The Dissolving ProcessThe dissolving process is facilitated by motion of liquid molecules and intermolecular forces.Liquid molecules are moving in random motion.When a molecule is dissolved in water, water molecules hydrogen bond with one another to form a cage to dissolve.

II. Like Dissolves LikeLike substances dissolve like substances If something has a charge, then it will not be able to dissolve something that does not have a charge.

SUMMARIZE

A ProblemCools down to room temperatureGross!

Justify TPSWhy does this solid appear at cold temperatures, but it wasnt present when the cider was hot?

Sugar Cube InvestigationWe can make statements about what we think is the answer to a question, but a good scientist experimentsYou are going to be doing an investigation with your group to determine how surface area and temperature impact the rate at which something dissolves.

Lab ConductFollow the procedure that has been given to youRespect the equipment. It costs a lot of money to replace this stuffUse the chemicals in a responsible and safe wayClean up the space when you are doneRead the steps, they will tell you what to do.

Lab Work Time

Lab DebriefWhat happens to the rate at which the sugar dissolved as you increased the temperature?What happens to the rate at which the sugar dissolved as you increased the surface area?Why?!?!?!

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

I. DissolvingWe 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 DissolvingAs 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 RateCold liquidHot liquid

III. Surface Area and DissolvingAs 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 TPSWhy does your soda become carbonated when you open it? What is happening?

IV. Pressure and DissolvingAs 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 DissolvingWhen 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

How does salt dissolve water? clip*Open a soda to demonstrate that carbonation is induced*