Chapter 2 Notes II CHEMICAL AND PHYSICAL CHANGES

IV. Scientific Method The process researchers use to carry out their investigations. It is a logical approach to solving problems.

A. Steps 1. Ask a question 2. Observe and collect data 3. Formulate a hypothesis (a testable if-then statement). The hypothesis serves as a basis for making predictions and for carrying out further experiments. 4. Test your hypothesis – Requires experimentation that provides data to support or refute your hypothesis.

B. Terms to Know 1. Law vs. theory Scientific (natural) Law: a general statement based on the observed behavior of matter to which no exceptions are known. Theory: a broad generalization that explains a body of facts or phenomena.

1. Quantitative vs. qualitative data Quantitative: numerical (mass, density) Quantity - number + unit Qualitative: descriptive (color, shape)

Chemistry – the study of MATTER I. Chemistry: The branch of science that deals with the identification of the substances of which matter is composed; the investigation of their properties and the ways in which they interact, combine, and change; and the use of these processes to form new substances. (Matter = anything that has mass and takes up space)

PROPERTIES OF MATTER What is matter? What is mass? Anything that has mass and takes up space The amount of matter an object contains

Chemical Composition mixture or “pure substance”? Before we can even begin to consider matter from a chemical point of view, we need to know something about its composition; is the stuff I am looking at a single substance, or is it a mixture? Think of a sample of salt (sodium chloride) as opposed to a solution of salt in water— a mixture of salt and water.

SUBSTANCES A substance is matter that has a definite and uniform composition One type of “stuff”

MIXTURES A mixture is a physical blend of two or more substances. They can be physically separated. How? One type of “stuff” More than one type of “stuff” together

HETEROGENEOUS vs. HOMOGENEOUS There are two different types of mixtures. A heterogeneous mixture is one that has more than one phase (part of uniform composition) A homogeneous mixture has only one phase.

Mixtures: matter that can be physically separated into component parts (pure substances). a. homogeneous mixture –has uniform composition; also called a solution b. heterogeneous mixture – does not have a uniform composition CuSO 4 Solution Orange Juice Oil and Water

MIXTURES Not uniform Uniform throughout physically separable

HETEROGENEOUS OR HOMOGENEOUS? Saltwater Spaghetti sauce Muddy water Cough syrup Salad Brass

TYPES OF SUBSTANCES There are two different types of substances: AND

ELEMENTS An element is the simplest forms of matter. Each element is represented by a chemical symbol.

COMPOUNDS A compound is a substance that can be separated into simpler substances only by chemical means

Pure Substances: when component parts of a mixture can no longer be physically separated into simpler substances. Pure substances are either compounds or elements. a. Compounds – can be decomposed by a chemical change. Two or more elements bonded together. b. Elements – cannot be decomposed by a chemical change. Will appear no the periodic table. CuSO 4 Cu

TYPES OF MATTER physically separable chemically separable

III. Classification of Matter Matter Can it be physically separated? Yes No MixturesPure Substances Is the composition uniform?Can it be decomposed by an ordinary chemical reaction? Yes No Homogeneous HeterogeneousCompounds Elements Mixtures Mixtures (water, sodium (gold, oxygen, (Solutions) (Suspensions chloride, sucrose) carbon) (air, sugar water, or Colliods) salt water) (granite, wood, muddy water)

Techniques used for mixture separation: Filtration (sand from water) Centrifugation (butterfat from milk) Evaporation (salt from water) Distillation (water from salt) Chromatography (separating pigments in ink)

Filtration (sand from water)

Centrifuge Solid or liquid particles of different densities are separated by rotating them in a tube in a horizontal circle. The dense particles tend to move along the length of the tube to a greater radius of rotation, displacing the lighter particles to the other end.

Evaporation (salt from water)

Distillation A liquid is partly boiled away; the first portions of the condensed vapor will be enriched in the lower-boiling component.

Chromatography As a liquid or gaseous mixture flows along a column containing an adsorbent material, the more strongly- adsorbed components tend to move more slowly and emerge later than the less-strongly adsorbed components.

Two mutually-insoluble liquids, one containing two or more solutes (dissolved substances), are shaken together. Each solute will concentrate in the liquid in which it is more soluble. Liquid-liquid Extraction Liquid-liquid Extraction

PHYSICAL PROPERTIES color odor Density and hardness Melting point Boiling point solubility A quality or condition of a substance that can be observed or measured without changing the substance’s composition What are some examples?

II. Physical Properties of Matter Intensive - Properties that do not depend on the amount of the matter present. Ex: Color, Odor, Luster, Malleability, Ductility, Conductivity, Hardness, Melting/Freezing Point, Boiling Point, Density Extensive - Properties that do depend on the amount of matter present. Ex: Mass, Volume, Weight, Length Physical properties of matter are categorized as either Intensive or Extensive:

STATES OF MATTER Matter’s state is a physical property Definite shape, definite volume solid No definite shape, definite volume liquid No definite shape, no definite volume gas

SIDENOTE: A gaseous substance that is found as a solid or liquid at room temperature is called vapor.

PHYSICAL CHANGES A physical change is one that does not involve altering the chemical composition.

CHEMICAL REACTIONS The ability of a substance to react and form new substances is called a chemical property. In a chemical reaction, one or more substances change into new substances. A reaction starts with the reactants, and the substances formed are called products.

4 CLUES TO CHEMICAL REACTION Color change Gas formed Heat/light produced/ absorbed Solid from a liquid

CHEMICAL OR PHYSICAL CHANGE? Baking cookies Boiling water Dissolving salt Burning firewood Milk spoiling Metal rusting Tearing paper Melting ice

LAW OF CONSERVATION OF MASS During any chemical reaction, the quantity of matter is unchanged. The mass of the products always equals the mass of the reactants.