Mixtures

1. Mixtures Ch. 9, sec. 3 Science

2. Properties of Mixtures • A mixture is a substance made by combining two or more different materials in such a way that no chemical reaction occurs. • A mixture can usually be separated back into its original components. • No chemical reaction occurs when a mixture is made. • Some examples of mixtures are a tossed salad, salt water and a mixed bag of M&M's candy. • The properties of a mixture are similar to the properties of its components. • In some mixtures, such as salt water, you cannot see all the components.

3. Uniform or Non-Uniform • Mixtures that are uniform or homogeneous (all the same) are called solutions. • Mixtures that are not uniform throughout are heterogeneous.

4. There are 7 diatomic elements. What are they and what group(s) are they found?

5. Separating Mixtures • There are several ways to separate mixtures: • 1. evaporation - heat the mixture • 2. distillation – based on the boiling points of the components • 3. magnet – used to separate components of mixed magnetism • 4. centrifuge – uses densities of components

6. Mixtures vs. Compounds • Mixtures • Made of elements, compounds, or both • No change in original properties of components • Separated by physical means • Formed using any ratio of components • Compounds • Made of elements • Change in original properties of components • Separated by chemical means • Formed using a set ratio of components

7. Solutions • A solution is a mixture that appears to be a single substance. It is composed of particles of two or more substances that are distributed evenly among each other. • A solution has the same appearance and properties throughout the mixture. • In solutions, the solute is the substance that is dissolved. • The solvent is the substance in which the solute is dissolved. When two liquids or two gases form a solution, the substance that is present in the largest amount is the solvent. • Soluble means able to dissolve and insoluble means unable to dissolve. • Ex: salt water – salt (solute) is soluble in water (solvent)

8. Examples of Solutions • Not all solutions are liquids. Solutions may also be gases, such as air. • Solutions may be solids, such as steel. Alloys are solid solutions of metals or nonmetals dissolved in metals. (Ex: brass is metal zinc dissolved in copper) • Other examples of solutions: • Gas in gas = dry air (oxygen in nitrogen) • Gas in liquid = soft drinks (carbon dioxide in water) • Liquid in liquid = antifreeze (alcohol in water) • Solid in liquid = salt water (salt in water – duh!) • Solid in solid = brass (zinc in copper)

9. Particles in Solutions • Particles in solutions are so small they never settle out. • They cannot be removed by filtering • They do not scatter light. • The measure of the amount of solute dissolved in a solvent is concentration. • Concentration can be expressed in grams of solute per milliliter of solvent (g/mL) • Solutions can be concentrated (more solute) or dilute (less solute)

10. Solubility • The solubility of a solute is the ability of the solute to dissolve in a solvent at a certain temperature. • Most solids are more soluble in liquids at higher temperatures. • Gases become less soluble in liquids as the temperature is raised. (a warm soft drink goes flat faster) • Several things affect how fast a solid will dissolve: • Mixing – stirring or shaking causes particles to separate and spread out • Heating – causes particles to move more quickly and spread out • Crushing – increases the amount of contact it has with the solvent

11. Suspensions • A suspension is a mixture in which particles of a material are dispersed throughout a liquid or gas but are large enough that they settle out. • The particles are large enough to scatter or block light. • The particles are too large to stay mixed without being stirred or shaken. • If allowed to sit, the particles will settle out. (Ex: snow globe) • A suspension can be separated by passing it through a filter.

12. Colloids • A colloid is a mixture in which the particles are dispersed throughout but are not heavy enough to settle out. • The particles are relatively small and are fairly well mixed. • Ex: milk, mayonnaise, stick deodorant, Jell-O • The particles in a colloid are much smaller than those in a suspension, but large enough to scatter light. • Particles cannot be separated by a filter.