Chemistry Unit 2: Matter and its changes

Chemistry is… Combustion reaction: …the study of the composition, structure, and properties of matter and the changes it undergoes Combustion reaction: C2H5OH + 3 O2  2 CO2 + 3 H2O + Energy Reactants  Products

Matter Introductory Definitions matter: anything having mass and volume mass: the amount of matter in an object volume: the space an object occupies units: L, dm3, mL, cm3 properties: describe the matter what it looks like, smells like; its mass, temp., etc. how it behaves

Properties of Matter Extensive properties depend on the amount of matter that is present. Extensive properties Volume Length Height Mass Energy Content (think Calories!) do not depend on the amount of matter present. Intensive properties Melting point Color Odor Conductivity Malleable Ductile Boiling point Density

PHYSICAL PROPERTIES characteristics that can be observed without changing the identity of the substance. Examples: mass volume color shape texture density

CHEMICAL PROPERTIES describe the tendency of a substance to undergo chemical change(s), or transform into new substances Examples: flammability reactivity

Change in material (taste; bacterial growth) Property: Chemical (reason): Physical (reason): Luster Surface of metal becomes dull when exposed to air N2 reacts with high temperature of a car engine and makes nitrogen oxides Milk turns sour when left out of fridge too long Diamonds are hard enough to use as drill bits No change in material Metal reacts with oxygen New substance formed Change in material (taste; bacterial growth) No change in material

Physical Change A change in a substance that does not involve a change in the identity of the substance. Example: Phase Changes (liquid to gas) Evaporation allows the solvent to be removed from the solute by boiling.

Chemical Change A change in which one or more substances are converted into different substances. Heat and light are often evidence of a chemical change.

Chemical Change Chemical Change on the atomic level Na Cl Na+ Cl- So, which of these would be a chemical change? - Grape juice after it has been left in the car for a few days during a hot summer. - Logs burning in a fireplace. - Toasting a bagel in the morning for breakfast.

Evidence of Chemical Change Key to a chemical reaction is the formation of a new substance *Evidence of new substance (s): gas is produced new taste, smell, or sound is produced light and/or electricity is produced color changes temperature changes Precipitate forms a solid that forms from a solution during a chemical reaction. These evidences do not always work

Evaporation is a physical change

Breaking is a physical change.

Boiling is a change of state, and therefore a physical change!

Rusting is a Chemical Change

Burning is a Chemical Change

Phase Differences Solid – definite volume and shape; particles packed in fixed positions. Liquid – definite volume but indefinite shape; particles close together but not in fixed positions Gas – neither definite volume nor definite shape; particles are at great distances from one another Plasma – high temperature, ionized phase of matter as found on the sun.

Some Properties of Solids, Liquids, and Gases Property Solid Liquid Gas Shape Has definite shape Takes the shape of Takes the shape the container of its container Volume Has a definite volume Has a definite volume Fills the volume of the container Arrangement of Fixed, very close Random, close Random, far apart Particles Interactions between Very strong Strong Essentially none particles

Energy Changes Accompanying Phase Changes Gas Vaporization Condensation Sublimation Deposition Energy of system Liquid Melting Freezing Solid Brown, LeMay, Bursten, Chemistry 2000, page 405

Classification of Matter Elements Draw this chart!, leave space to define the terms Pure Substances Compounds Matter Homogeneous Mixtures Heterogeneous

sodium chloride (NaCl) Classifying Matter (Pure) Substances …have a fixed composition …have fixed properties ELEMENTS COMPOUNDS e.g., Fe, N2, S8, U e.g., H2O, NaCl, HNO3 sulfur (S8) sodium chloride (NaCl) Pure substances have a chemical formula.

retain their individual properties. Mixtures two or more substances mixed together …have varying composition …have varying properties The substances are NOT chemically bonded, and they… retain their individual properties. Tea, orange juice, oceans, and air are mixtures.

Two Types of Mixtures homogeneous: (or solution) particles are microscopic; sample has same composition and properties throughout; evenly mixed Kool Aid salt water e.g., alloy: a homogeneous mixture of metals bronze (Cu + Sn) pewter (Pb + Sn) brass (Cu + Zn) e.g.,

Two Types of Mixtures (cont.) heterogeneous: different composition and properties in the same sample; unevenly mixed raisin bran tossed salad e.g., suspension: settles over time snowy-bulb gifts paint e.g.,

EXAMPLES What type of matter are each of the following… ?

SAND

SAND Heterogeneous mixture

Salt (NaCl)

Salt (NaCl) COMPOUND

Air

Air Homogeneous mixture of: Nitrogen, N2 78.08% Oxygen, O2 20.95% Argon, Ar 0.93% Carbon dioxide, CO2 0.033% Neon, Ne 0.0018% Helium, He 0.00052% Methane, CH4 0.0002% Krypton, Kr 0.00011% Nitrogen(I) oxide, N2O 0.00005% Hydrogen, H2 0.00005% Xenon, Xe 0.0000087% Ozone, O3 0.000001% Homogeneous mixture of: Many gases make up mixture, but it looks like it is all one gas.

Gold

Gold ELEMENT: Au

Bronze

Bronze Homogeneous mixture of copper and tin (alloy: mixture of metals)

Salad Dressing

Salad Dressing: Heterogeneous

Separation of a Mixture The constituents of the mixture retain their identity and may be separated by physical means.

…involves physical means, or physical changes Separating Mixtures …involves physical means, or physical changes 1. sorting: by color, shape, texture, etc. Mixture of solid and liquid Filtrate (liquid component of the mixture) Filter paper traps solid Funnel 2. filter: particle size is different

Separating Mixtures (cont.) 3. magnet: one substance must contain iron 4. chromatography: some substances dissolve more easily than others

Separating Mixtures (cont.) 5. density: “sink vs. float” perhaps use a centrifuge blood after high- speed centrifuging decant: to pour off the liquid

Separating Mixtures (cont.) 6. distillation: different boiling points heat source thermometer water in (cooler) water out (warmer) more-volatile substance mixture condenser substance, now condensed (i.e., the one with the lower boiling point)

Spin sample very rapidly: denser materials go to bottom (outside) 7. Centrifugation Spin sample very rapidly: denser materials go to bottom (outside) Separate blood into serum and plasma Serum (clear) Plasma (contains red blood cells ‘RBCs’) Check for anemia (lack of iron) AFTER Before Blood Serum RBC’s A B C

are needed to separate mixtures; substances are NOT bonded. No chemical reactions are needed to separate mixtures; substances are NOT bonded. dental amalgam