Classifying Materials

Unit #2

MatterDef: anything that takes up space and has mass

States of MatterSolid

Has definite shape and volumeParticles 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.

GasFlowsTakes the shape AND volume of the container (Indefinite shape and volume)Particles are spaced far apart and easily compressedVapor

Substance in the gaseous state that is a solid or a liquid at room temperature

Example: steam

States of Matter with Named Changes

SubstancesDef: Matter that has a uniform and unchanging composition (pure substance)Examples

Table Salt: always sodium and chlorideWater: always hydrogen and oxygenNOT sea water…why not?

Pure SubstancesDef: matter that has a uniform and unchanging compositionTwo types:

Elements Cannot be separated into simpler substances Contain all the same atoms Ex: C, Al, Cu, Hg, Au

Elements92 naturally occurring on EarthUnique name and symbolDmitri Mendeleev organized 1st periodic tablePeriods = horizontal rowsGroups 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

MixturesDef: a combination of two or more pure substances in which each pure substance retains its individual chemical propertiesTwo Types of Mixtures:

HeterogenousHomogenous

Heterogeneous Mixture

Mixture that is not completely uniformIndividual substances remain distinct

Homogeneous MixtureMixture that is uniform throughoutParticles are evenly mingledaka Solutions –

Def: homogeneous mixture of 2 or more substancesContain very small particles1. Solvent – dissolving agent (usually a liquid)2. Solute – substance being dissolved (usually a solid)

Aqueous solution – any solution whose solvent is waterExamples:

• Salt and water• Air – mixture of gases• Alloys

Homogeneous Mixture - AlloyDef: A homogenous mixture of metals, or a mixture of one metal and one nonmetal, in which the metal substance is the major componentUsed by manufactures to achieve greater strength and durabilityUsed in spacecrafts and automobiles

Techniques Used for SeparationFiltration

Separates a liquid from a solid (heterogeneous mixtures)Distillation

Physically separates most homogeneous mixtures based on boiling point differences of the substances

CrystallizationProduces pure solid particles of a substance from a solution that contains the dissolved substance

ChromatographySeparates components of a mixture on its ability to travel or be drawn across the surface of another material

E le m e n ts C o m p o un ds

P u re S ub s tan ces

S o lu tio ns

H o m o ge n eo us H e tero ge n eo us

M ix tu res

Matter

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 ProportionsAtoms 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 ClIn 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

ExampleA 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 ProportionsColumn 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%

Percent by mass (%) = mass of element x 100 mass of compound

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 OxygenPeroxide (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 12.01 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 ChangesDef: Change that alters at least one of the physical properties of the substanceDoes not change the chemical compositionExamples:

Changing the physical state – i.e. freezing, melting, etc.DissolvingAltering the shape or size

Physical propertiesDef: 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 changesDef: a change in the chemical composition of a substance (cannot go back to original form)Occurs as a chemical reactionExamples:

Iron rusting to form iron (III) oxideFermentation of grape juice

Chemical propertiesDef: the ability of a substance to undergo chemical reactions and to form new substancesExamples:

Rusting is a chemical property of ironAbility 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 MassDef: States that mass is neither created nor destroyed during a chemical reaction; it is CONSERVEDMass reactants = Mass products

H2 + O2 H2O

reactants productsTotal mass started is the same at the end