Classifying Materials Unit #2

Matter Def: anything that takes up space and has mass

States of Matter Liquid Solid Flows (takes the shape of its container) Has definite shape and volume Particles are tightly packed and locked in place (incompressible) Not defined by rigidity or hardness Liquid Flows (takes the shape of its container) Indefinite shape Constant/Definite volume Expands when heated Virtually incompressible Takes the shape of the container Particles are less closely packed; can move past each other

States of Matter cont. Gas Flows Takes the shape AND volume of the container (Indefinite shape and volume) Particles are spaced far apart and easily compressed Vapor Substance in the gaseous state that is a solid or a liquid at room temperature Example: steam

States of Matter with Named Changes

Substances Def: Matter that has a uniform and unchanging composition (pure substance) Examples Table Salt: always sodium and chloride Water: always hydrogen and oxygen NOT sea water…why not?

Pure Substances Def: matter that has a uniform and unchanging composition Two types: Elements Cannot be separated into simpler substances Contain all the same atoms Ex: C, Al, Cu, Hg, Au

Elements 92 naturally occurring on Earth Unique name and symbol Dmitri Mendeleev organized 1st periodic table Periods = horizontal rows Groups or families = vertical rows

Pure Substances cont. Compounds Combination of 2 or more elements Can be broken down into elements by a chemical reaction Ex: H2O, NaCl, CO2, etc. Properties of elements are different than when they form compounds Molecules – smallest particle of a compound or element

Mixtures Def: a combination of two or more pure substances in which each pure substance retains its individual chemical properties Two Types of Mixtures: Heterogenous Homogenous

Heterogeneous Mixture Mixture that is not completely uniform Individual substances remain distinct

Homogeneous Mixture Mixture that is uniform throughout Particles are evenly mingled aka Solutions – Def: homogeneous mixture of 2 or more substances Contain very small particles Solvent – dissolving agent (usually a liquid) Solute – substance being dissolved (usually a solid) Aqueous solution – any solution whose solvent is water Examples: Salt and water Air – mixture of gases Alloys

Homogeneous Mixture - Alloy Def: A homogenous mixture of metals, or a mixture of one metal and one nonmetal, in which the metal substance is the major component Used by manufactures to achieve greater strength and durability Used in spacecrafts and automobiles

Techniques Used for Separation Filtration Separates a liquid from a solid (heterogeneous mixtures) Distillation Physically separates most homogeneous mixtures based on boiling point differences of the substances Crystallization Produces pure solid particles of a substance from a solution that contains the dissolved substance Chromatography Separates components of a mixture on its ability to travel or be drawn across the surface of another material

Joseph Proust (France 1799) Law of Definite Proportions: A given compound always contains elements in a certain proportion by mass. (Constant composition).

Law of Definite Proportions Atoms combine in whole number ratios, so their proportion by mass will always be the same. Example: H2O is always made up of 2 atoms of H and one atom of O. The ratio of O to H in water is always (15.9994:2.01588) which is 16:2 or 8:1.

Example Law of Definite Proportions : KCl always contains one atom of K for every one atom of Cl In KCl, potassium and chlorine always have a ratio of (39.0983 to 35.4527) or ~1:1 by mass.

Law of Definite Proportions Formula: Percent by mass (%) = mass of element x 100 mass of compound

Example A compound of sucrose is made up of the elements carbon, hydrogen, and oxygen. Carbon makes up 8.44 grams, hydrogen makes up 1.30 grams, and oxygen makes up 10.26 grams. Find the percent by mass of each of the elements in the compound.

Law of Definite Proportions Percent by mass (%) = mass of element x 100 mass of compound Law of Definite Proportions Column 1 Column 2 Element Analysis by mass (g) Percent by mass (%) Carbon 8.44 g carbon 8.44 g Carbon x 100 20.00 g Sucrose = 42.20% Carbon Hydrogen 1.30 g hydrogen 1.30 g Hydrogen x 100 20.00 g Sucrose = 6.50% Hydrogen Oxygen 10.26 g oxygen 10.26 g Oxygen x 100 20.00 g Sucrose = 51.30% Oxygen Total 20.00 g sucrose = 100%

Law of Multiple Proportions (John Dalton) When the same two elements combine to form more than one compound: the ratios of the mass of one element in the first compound to its mass in the second compound, (as it combines with the same mass of the other element), can always be expressed as ratios of small whole numbers( ex: 1:3 or 2:5). Example Water (H2O) = 2:1 Hydrogen to Oxygen Peroxide (H2O2) = 2:2 Hydrogen to Oxygen

Example of Law of Multiple Proportions Carbon combines with oxygen to form CO and CO2 . Mass of Carbon(g) Mass of Oxygen(g) Ratio of O in CO2 to O in CO CO 12.01 16.00 CO2 32.00 2:1

Example In the carbon compounds ethane (C2H6) and ethene (C2H4), what is the lowest whole number ratio of H atoms that react with the same number of C atoms? Answer: 3:2

Physical Changes Def: Change that alters at least one of the physical properties of the substance Does not change the chemical composition Examples: Changing the physical state – i.e. freezing, melting, etc. Dissolving Altering the shape or size

Physical properties Def: Observed or measured without changing the chemical composition or identity of the substance Intensive Doesn’t depend on the amount of the substance Always remain the same for a given substance Ex: melting point, boiling point, density Extensive Depends on how much matter is being considered Ex: mass, volume, size Also, properties that can change for a substance Ex: color, state, shape

Chemical changes Def: a change in the chemical composition of a substance (cannot go back to original form) Occurs as a chemical reaction Examples: Iron rusting to form iron (III) oxide Fermentation of grape juice

Chemical properties Def: the ability of a substance to undergo chemical reactions and to form new substances Examples: Rusting is a chemical property of iron Ability to rot, rust, decompose, ferment, corrode, grow, and decay Physical changes indicate a chemical change has occurred Ex: heat, light, flame, gas bubbles, changes in color, formation of a solid, etc.

Law of Conservation of Mass Def: States that mass is neither created nor destroyed during a chemical reaction; it is CONSERVED Mass reactants = Mass products H2 + O2 H2O reactants products Total mass started is the same at the end