PreAP Chemistry. Unit 1 Matter and Change

Transcription

1 PreAP Chemistry Unit 1 Matter and Change

2 Scientific Method The scientific method is one logical approach to the solution of scientific problems. It involves observations, hypotheses, and experiments.

3 Theory vs Law A theory is a broad and extensively tested explanation of WHY a series of experiments give certain results. (usually explains things that we cannot see.atomic theory) A scientific law is a concise statement that SUMMARIZES the results of many observations and experiments. (usually explains things that we can see.gas laws)

4 Matter Matter is defined as anything that has mass and volume. The mass of an object is the amount of matter the object contains. The volume of an object is the space that it takes up. EVERYTHING is made up of matter.

5 (Pure) Substance A substance is matter that has a uniform and definite composition. A substance can be an element or a compound. Substances are also referred to as pure substances because they contain only one kind of matter. All samples of a substance have identical physical properties.

6 Physical Property A physical property is a quality or condition of a substance that can be observed or measured without changing the substance s composition. Ex. Color Density Solubility Melting Point Odor Boiling Point Shape Mass

7 Three States of Matter

8 Solid, liquid, and gas A solid is matter that has a definite shape and a definite volume. The particles cannot move other than vibrate. A liquid is a form of matter that flows, has a fixed volume, and takes on the shape of its container. These particles can tumble over each other. A gas is a form of matter that takes on both the shape and the volume of its container. These particles are flying all over the place.

9 Gas vs Vapor A gas and a vapor look the same.particles flying all over the place. A gas is normally a gas at room temperature. Ex. Oxygen, Carbon dioxide A vapor is normally a solid or liquid at room temperature Ex. Water vapor, gasoline fumes

10 Physical Change A physical change alters a given material without altering its composition. Ex. Bending pipe, flattening metal, cutting paper, pumping oil, dissolving sugar in water, changing physical state (melting, freezing, boiling, condensing, subliming, depositing)

11 Mixture A mixture is a physical blend of two or more substances. These mixtures can be either homogeneous or heterogeneous. These mixtures contain phase(s). A phase is any part of a system that has uniform composition and properties.

12 Homogeneous Mixtures A homogeneous mixture is one that has a completely uniform composition; that is, has only one phase (that is, it looks the same throughout). Examples include salt water, Kool Aid, tap water, air, brass Homogeneous mixtures are also known as solutions. Solutions can be solid, liquid, or gaseous. (brass, Kool Aid, air)

13 Heterogeneous Mixture A heterogeneous mixture is one that is not uniform in composition; that is, has more than one phase. Examples include blood, M&M blizzard, most soups, granite, concrete

14 How to separate mixtures? Heterogeneous mixtures can sometimes be easily separated. Filtration Picking vegies out of soup. Homogeneous mixtures are somewhat more difficult to separate. One way to separate is by distillation, which involves separating liquids from a mixture by using boiling points of the various liquids within the mixture.

15 Pure Substances Elements and Compounds Elements are the simplest forms of matter that can exist under normal lab conditions. Elements cannot be separated into simpler substances by chemical means Each element is represented by a one or twoletter chemical symbol. (ex. Fe not FE) Compounds are a chemical combination of two or more elements. Compounds can be separated by chemical means.

16 Matter Substances Definite composition Physically separable Mixtures of Substances Variable Composition Homogeneous mixture (also known as solutions: examples such as air, tap water Heterogeneous mixture (distinct phases: examples are soup, concrete, granite Element (Examples: iron, sulfur, carbon, oxygen Chemically separable Compound (Examples: water, iron II sulfide, aluminum sulfate

17 Know the 6 phase changes Melting solid changes to liquid Freezing liquid changes to solid Boiling liquid changes to gas Condensing gas changes to liquid Subliming solid changes to gas Direct change does not melt first Depositing gas changes to solid Direct change does not condense first

18 Chemical Reactions In a chemical reaction, one or more substances change into new substances. The starting substances are known as the reactants. The ending substances are known as the products. Therefore Reactants Products

19 Chemical Property A chemical property is the ability of a substance to undergo a chemical reaction in order to form a new substance. (rust) Chemical properties are observed only when a substance undergoes a chemical change. A chemical change always results in a change in the chemical composition of the substances involved.

20 Law of Conservation of Mass The law of conservation of mass states that in any physical or chemical change, mass is neither created or destroyed. Bottom Line? The mass of the reactants must equal the mass of the products. 1CH 4 + 2O 2 1CO 2 + 2H 2 O 16g + 64g = 44g + 36g 80g = 80g

21 Signs that indicate a physical chg Was there a change in the shape or form of the substance? (ie. Flattened) Did the substance change its location? Was the substance dissolved in a liquid? Was there a change of state? Melting (s to l) or freezing (l to s) Boiling (l to g) or condensing (g to l) Subliming (s to g) or depositing (g to s)

22 Signs that indicate a chemical chg IF, after mixing two or more substances Was energy absorbed or released? (hot or cold) Was a gas released? (bubbles?) Was a solid produced? (cloud that settles) Was there a change in color or odor? Did the appearance of the surface of a solid change? (such as rust on a nail)