Classifying Materials Unit #2
Mar 27, 2015
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