Discuss reaction of zinc and hydrochloric acid to produce a gaseous product. Determine that it involves both a physical and chemical change. The physical change was the change of the solid zinc a soluble solute, and the chemical change involved the production of a gaseous product, hydrogen. Discuss some physical and chemical reactions, like the electrolysis of salt to produce a soft metal and a green gas. Write the formulas for sodium chloride solution reacting with silver nitrate solution to produce the photographic precipitate silver chloride which is used in the manufacturing of film.
Review definitions of molar mass, density and square root determination using a calculator, Define the rate of diffusion of gases as the being inversely proportional to the square root of the molar mass of the gases. Write the formula. Determine that a gas which is 4 times the molar mass of a second gas would diffuse through a pinhole at 1/2 the rate. Use an example of hydrogen gas and oxygen gas in a container. Determine that the hydrogen molecules would diffuse 4X faster than the oxygen molecules.
Begin discussion on chemical and physical changes in matter using Zn and HCl as examples.
View and discuss Brownian movement of particles. Discuss how the constant molecular motion allows colloids and suspensions to remain in heterogenous solution. View the Tyndall effect which demonstrates the Browniam motion of particles ranging in size from suspension to colloidal size. Introduce Graham's law of effusion and diffusion of gases and the rate being dependent on molecular mass ratio.
Discuss why the particles in a colloid are prevented from settling out. Introduce the concept of polarity and charged atoms. Use diagrams to show how areas on the surface of the colloid molecule attract positive or negative charged areas of the dispersing medium. The layers repel each other and prevent settling out. Indicate why heating and stirring will interfere with the colloid particles and cause settling out. See diagrams to explain the Tyndall effect and the electrostatic layers.
