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Unit 2 Matter and Change General Chemistry Fall ‘10 Physical Properties All types of matter will have certain characteristics that never change. Some examples are: density, boiling point, freezing point, etc. We call these Physical Properties. Types of Physical Properties Intensive Do not depend on the size or shape of the sample Examples? Color, hardness, BP, etc. Extensive Depend on the sizes of the sample Examples Length, mass, volume, etc. Density • Amount of matter in an amount of space ▫ d = m/V ▫ How tightly particles are packed together Particles in a cotton ball Particles in a bowling ball • Use triangle to figure out which equation to use • If you are given mass and density, you can figure out the volume by covering up the volume triangle So Volume = Mass(g) Density(mL) ? Density M D = V M M = DxV ass D ensity V olume M V = D Lets try some problems An irregular object with a mass of 18 kg displaces 2.5 L of water when placed in a large overflow container. Calculate the density of the object. Givens: Equation: m=18 kg D=m/v v=2.5L D=? kg/L Substitution: ? Kg/L = 18 kg/2.5 L Answer with unit 7.2 kg/L • A brick with a mass of 14 g measures 12 cm x 4 cm x 3 cm. Calculate the density of the object. Givens: Equation: Substitution: Answer with unit A bar of gold with a density of 5 g/ml has a volume of 500 mL. Calculate the mass. Givens: Equation: Substitution: Answer with unit Measuring Density for square objects • Find the mass using a balance • Length x width x height • But what if it’s weird looking? Density of odd-shaped Objects • Find the mass using a balance Graduated cylinder, beaker to find volume • Use ______________________. Kinetic Molecular Theory Kinetic = Movement (Energy) Molecule = Particles The more energy in a substance, the faster the particles move. ALL particles in a substance are constantly in motion. Kinetic Molecular Theory Matter • Any substance that has mass and occupies space. • 3 States… Phases of Matter • Solids ▫ Solids are the least energetic phase of matter ▫ Solids have a definite volume and a definite shape. Phases of Matter (cont.) • Solids ▫ The particles are packed tightly together and stay in one position. The particles vibrate slightly between each other… so they’re not completely motionless. Phases of Matter • Liquids ▫ Liquids have a medium amount of energy (more than solids, less than gases) ▫ Liquids have a definite volume but not a definite shape. They take on the shape of the container Phases of Matter • Liquids ▫ The particles are somewhat packed together and move around one another. Phases of matter • Gases ▫ Gases are the most energetic phase of matter ▫ Gases have no definite volume and no definite shape. Phases of Matter • Gases ▫ The particles are spread out and move around a lot. Recap Three States of Matter SOLID Low energy Fixed Shape Fixed Volume Indefinite Volume Loose particle attraction Can flow Lots of Energy Indefinite shape LIQUID GAS Phase Change Diagrams A, C, E = molecules change speed B, D = space between molecules changes Practice Problem • Which letters BD represent phase changes? • Which letters represent a states ACE of matter (phases)? • Which letters represent a change in kinetic energy? A C E Elements, Compounds, and Mixtures • Element • The simplest form of matter that has a unique set of properties • Can’t be broken down Elements, Compounds, Mixtures (cont.) • Compounds – 2 or more elements chemically combined in fixed proportions – Can be broken down chemically, not physically – Heat – Electricity – reactions – Examples of compounds: • NaCl, H2O, C12H22O11 Elements, Compounds, Mixtures (cont.) • Mixtures – When substances physically combine – Examples: • Cinnamon and sugar, French fries and ketchup Elements, Compounds, Mixtures (cont.) • 2 kinds of Mixtures: ▫ Heterogeneous A mixture in which the parts can be seen Looks different throughout ▫ Homogeneous Fruit Salad A mixture in which the parts can NOT be seen Looks the same throughout AKA- solutions Fruit Smoothie Practice Problem • Identify the following as: • 1. Beef and ▫ Element Vegetable Soup ▫ Compound Het. Mixture ▫ Heterogeneous mixture ▫ Homogeneous mixture • 2. Calcium chloride Compound • 3. Krypton Element • 4. Chocolate milk (well stirred) Hom. Mixture Physical Properties • Characteristics we observe without changing the makeup of the substance. • Important ones: ▫ Appearance, melting and boiling point, density, heat and electrical conductivity, solubility ▫ Physical state under normal conditions. Chemical Properties • Describes a substances chemical reactions with other substances. ex) Na reacts with O2 to form Na2O Na reacts with H2O to produce H2(g) The periodic table is organized by the elements’ chemical properties. Changing Matter • Physical Changes – Alters the form or appearance of a substance but does not make the material into another substance • Chemical Changes (aka: chemical reactions) Tearing Paper – A change in the chemical composition of a substance to produce a new material with new properties Burning Paper Chemical reactions • Reactant ▫ A substance present at the start of the reaction • Product ▫ A substance produced in the reaction How do you know? • Physical changes are observed without changing the substance. • Four clues of a chemical change ▫ ▫ ▫ ▫ transfer of heat Change in color Production of gas Formation of a precipitate (a solid that forms and settles out of a liquid mixture) Practice Problem • Identify the following as: • 1. Iron rusting ▫ Physical change Chem. Change ▫ Chemical change • 2. Melting ice cube Phys. Change • 3. Firework exploding Chem. Change • 4. Salt dissolving Phys. Change Conservation of Mass (**prediction**) • During a chemical reaction, the mass of the products is always equal to the mass of the reactants • Light a fire during winter ▫ Two products are CO2 and water vapor ▫ Where do they go?! • Law of Conservation of mass ▫ In any physical change or chemical reaction, mass is conserved ▫ Mass is neither created nor destroyed Methods of Separating Mixtures • • • • • • • Magnet Filter Decant Evaporation Centrifuge Chromatography Distillation Mixture of solid and liquid Filtration separates a liquid from a solid Stirring rod Funnel Filter paper traps solid Filtrate (liquid component of the mixture) Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40 Chromatography • Tie-dye t-shirt • Black pen ink • DNA testing ▫ Tomb of Unknown Soldiers ▫ Crime scene ▫ Paternity testing Paper Chromatography Separation by Chromatography sample mixture a chromatographic column stationary phase mobile phase selectively absorbs sweeps sample components down column http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld006.htm detector Separation by Chromatography sample mixture a chromatographic column stationary phase mobile phase selectively absorbs sweeps sample components down column http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld006.htm detector Ion chromatogram of orange juice detector response K+ Na+ 0 5 Mg2+ Fe3+ 10 15 time (minutes) 20 Ca2+ 25 Setup to heat a solution Ring stand Beaker Wire gauze Ring Bunsen burner Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 42 A Hero’s Fountain Glass retort mixture for distillation placed in here long spout helps vapors to condense Eyewitness Science “Chemistry” , Dr. Ann Newmark, DK Publishing, Inc., 1993, pg 13 Furnace A Distillation Apparatus thermometer liquid with a solid dissolved in it condenser tube distilling flask Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 282 hose connected to cold water faucet receiving flask pure liquid The solution is boiled and steam is driven off. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 39 Salt remains after all water is boiled off. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 39 No chemical change occurs when salt water is distilled. Distillation (physical method) Salt Saltwater solution (homogeneous mixture) Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40 Pure water Separation of a sand-saltwater mixture. Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 40 Separation of Sand from Salt 1. Gently break up your salt-crusted sand with a plastic spoon. Follow this flowchart to make a complete separation. Saltcrusted sand. Calculate weight of salt. Weigh the mixture. Weigh sand. Pour into heat-resistant container. Fill with water. Stir and let settle 1 minute. Decant clear liquid. Dry sand. No 2. How does this flow chart insure a complete separation? Evaporate to dryness. Yes Repeat 3 times? Wet sand. Four-stroke Internal Combustion Engine Different Types of Fuel Combustion Gasoline (octane) 2 C8H18 + 25 O2 16 CO2 + 18 H2O Methanol (in racing fuel) __CH3OH +__O2 __CO2 +__H2O Combustion Chamber -The combustion chamber is the area where compression and combustion take place. -Gasoline and air must be mixed in the correct ratio. The Advantages of Methanol Burning Engines •Methanol can run at much higher compression ratios, meaning that you can get more power from the engine on each piston stroke. •Methanol provides significant cooling when it evaporates in the cylinder, helping to keep the high-revving, highcompression engine from overheating. •Methanol, unlike gasoline, can be extinguished with water if there is a fire. This is an important safety feature. •The ignition temperature for methanol (the temperature at which it starts burning) is much higher than that for gasoline, so the risk of an accidental fire is lower. A Race Car - Basic Information •At 900 hp, it has about two to three times the horsepower of a "highperformance" automotive engine. For example, Corvettes or Vipers might have 350- to 400-horsepower engines. •At 15,000 rpm, it runs at about twice the rpm of a normal automotive engine. Compared to a normal engine, an methanol engine has larger pistons and the pistons travel a shorter distance up and down on each stroke. •The motor is lighter. This lowers their inertia and is another factor in the high rpm. Centrifugation • Spin sample very rapidly: denser materials go to bottom (outside) • Separate blood into serum and plasma AFTER Before ▫ Serum (clear) ▫ Plasma (contains red blood cells ‘RBCs’) Check for anemia (lack of iron) Serum Blood RBC’s A B C Water Molecules Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 8 The decomposition of two water molecules. Water molecules Diatomic oxygen molecule + Diatomic hydrogen molecules Electric current 2 H2O O2 + 2 H2 Electrolysis Water “electro” = electricity “lysis” = to split H2O(l) water *H1+ Oxygen gas forms Hydrogen gas forms O2 (g) + 2 H2 (g) oxygen hydrogen *Must add acid catalyst to conduct electricity Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 32 Source of direct current Electrode Electrolysis of Water D.C. power source oxygen gas hydrogen gas anode cathode Half reaction at the cathode (reduction): 4 H2O + 4 e - 2 H2 + 4 OH 1Half reaction at the anode (oxidation): 2 H2O O2 + 4 H 1+ + 4 e - water Reviewing Concepts Physical Properties • List seven examples of physical properties. • Describe three uses of physical properties. • Name two processes that are used to separate mixtures. • When you describe a liquid as thick, are you saying that it has a high or low viscosity? Reviewing Concepts Physical Properties • Explain why sharpening a pencil is an example of a physical change. • What allows a mixture to be separated by distillation? Reviewing Concepts Chemical Properties • Under what conditions can chemical properties be observed? • List three common types of evidence for a chemical change. • How do chemical changes differ from physical changes? Reviewing Concepts Chemical Properties • Explain why the rusting of an iron bar decreases the strength of the bar. • A pat of butter melts and then burns in a hot frying pan. Which of these changes is physical and which is chemical?