Unit 1 Matter and Change

Transcription

1 Scientific Method Unit 1 Matter and Change What is matter and how is it classified? How can matter be changed? I M TAD Identify a Problem Make a Hypothesis Test the Hypothesis (Perform an Experiment) Analyze the Data Draw Conclusions Sometimes a 6 th step is included in which you share your conclusions with others Scientific Method Hypothesis An educated guess Scientific Theory A hypothesis supported by many experiments Best explanation with data gathered Explains a phenomenon Scientific (Natural) Law Facts of nature accepted as truth Describes a phenomenon Scientific Method Controlled Experiment Tests hypothesis 1 variable at a time Not necessarily safe Contains a Control Group Doesn t receive the experimental treatment Used as standard for comparison Why is it important to test 1 variable at a time? Prove which variable affects results Scientific Method Independent Variable Variable in the experiment you change Test only 1 at a time Dependent Variable Variable in the experiment that only changes because you changed the independent variable The effect you are looking for Chemistry Chemistry The study of matter and the changes it undergoes Chemistry deals with the Submicroscopic world Things that we cannot see with the naked eye or even a microscope 1

2 Chemistry Chemistry Matter Anything with mass and volume Mass The amount of matter in an object Weight The effect of gravity on an object Volume Amount of space taken up by matter Branches of Chemistry 1. Organic Chemistry Study of carboncontaining compounds 2. Inorganic Chemistry Study of matter that does not contain carbon Mars Curiosity Organic Chemist Chemistry Branches of Chemistry 3. Biochemistry Processes of living things 4. Analytical Chemistry Components and composition of substances Ex: Quality Control 5. Physical Chemistry Laws of physics with substances Pure Substances Pure Substances Cannot be separated by physical means Every sample has the same characteristics Characteristics can identify substance Pure Substances Elements Made up of ONE type of Atom Smallest unit of an element that maintains the chemical identity of that element Smallest unit of matter with unique properties Can be found on the Periodic Table Ex: Carbon (C), Nitrogen (N), Calcium (Ca), <100 others Pure Substances Compounds Made up of two or more types of atoms Chemically bonded Can be broken down into simple, stable substances Must be chemical separation, not physical separation Ex: water (H 2 O), sugar (C 12 H 22 O 11 ), salt (NaCl), etc. 2

3 Mixture Blend of two or more kinds of matter (elements and/or compounds) Each substance retains its own identity and properties Homogeneous Also known as Solutions Have uniform composition Same all the way through Particles are too small to be seen Examples: saltwater, tea Alloys Solid solutions that contain at least 1 metal Blended together so they have more desirable properties Common Alloys: Stainless Steel: iron, chromium, and zinc Bronze: tin and copper Heterogeneous Do not have uniform composition You can see the particles in them Examples: Italian Dressing (oil, water, vinegar, veggies) Soil (dirt, rocks, worms, etc.) Suspensions Heterogeneous mixture Solid particles eventually settle out of solution Examples: Muddy water of two solids Italian Dressing Colloid Heterogeneous mixture Won t separate upon standing Can t be separated by filtration Shows Tyndall Effect Scattering of light Sometimes mistaken for solutions Ex: paint, dairy, Jello 3

4 Properties of Matter All pure substances have characteristic properties Properties are used to distinguish between substances Properties are also used to separate substances Physical Property Characteristic observed/measured without changing substance s composition Describe the substance itself Physical Properties Physical Properties State of matter Color Mass, shape, length, volume Density Malleability ability to bend/hammer into thin sheet Ductility ability to make wire Magnetism Melting/boiling point, etc. States of Matter Solids Particles packed tightly together and held in fixed positions Definite shape and definite volume Lowest energy, highest structure Particles vibrate about fixed points States of Matter Liquids Definite volume Takes the shape of its container Ex: Milk in a glass vs. a gallon jug Particles can move past each other (Fluid) Fluid Anything that can be poured Particles move more rapidly than in a solid States of Matter Gases No definite shape Takes the shape of its container No definite volume Can be compressed Fluid Particles are spread far apart and move past each other rapidly 4

5 Plasma 4 th state of matter Similar to charged gas Found in stars, lightning, neon signs, and television Rarely occurs naturally on Earth States of Matter Chemical Properties Chemical Property Indicates how a substance will react with another Can be a failure to react Determined by changing substance s identity Ex: Iron Rusting Silver Tarnishing Chemical Properties Reactivity w/ a substance Combustibility burn in air Flammability burn Toxicity Oxidation Decomposition Intensive/Extensive Properties Extensive properties Depend on the amount of matter that is present Examples: energy in a substance, volume, mass Intensive properties Do not depend on the amount of matter present Examples: density, melting point, color Qualitative/Quantitative Data Physical Changes Qualitative Data Data we observe without measuring Ex: Physical State, Color, Shape, Sound, Smell, texture Quantitative Data Data that is measured with numbers Ex: length, mass, volume, density Physical Change Change in a substance that does not alter the substance s identity Examples: Grinding Cutting Mixing/Dissolving Changes of State 5

6 Changes of State Changes of State Melting Solid becomes a liquid Freezing Liquid becomes a solid Melting and Freezing Points are the SAME TEMPERATURE Condensation Gas becomes a liquid Boiling Liquid becomes a gas Condensation and Boiling Points are the SAME TEMPERATURE Sublimation Solid becomes a gas Ex: dry ice, air fresheners, freeze drying Deposition Gas becomes a solid Iodine, frost Changes of State Chemical Change One or more substances are converted into different substances Always results in new substances with different properties Most are Irreversible Chemical Changes Signs of a Chemical Change A gas is released (evolved) May be visible or detected as an odor Signs of a Chemical Change A Precipitate is formed Solid falls out of solution 6

7 Signs of a Chemical Change Signs of a Chemical Change Color change Only chemical if resulting solution is different color from ALL of its components A substance disappears Is consumed Dissolving is NOT a chemical change Signs of a Chemical Change Temperature Change Can also be light Endothermic Energy is absorbed by system Feels cold Ex: ice pack Exothermic Energy released as heat or light We can separate the components of a mixture by using their characteristic properties Boiling/freezing point, density, solubility, state of matter, etc. Decanting Pouring off liquid without disturbing the sediment or other liquid layers Usually used to separate solids from liquids Can be used to separate two liquids Decanting Use a glass stirring rod to: Keep the solid from pouring out Allow liquid to run down it and avoid splashing 7

8 Evaporation Used to separate a solid from a liquid in a solution Solution is heated until all of the liquid evaporates and solid is left behind Magnetic Properties Two substances can be separated if: One substance is magnetic and the other is not Magnet will attract one substance but not the other Filter Membrane that allows some substances to pass through while blocking others Separates insoluble solids from liquids Most common type is Gravity Filtration Another is Vacuum Filtration Distillation Separates two liquids with different boiling points When liquid boils, it evaporates and reaches the condenser Water runs along outside of condenser to cool vapor Liquid is collected at other end Chromatography Separates components of a solution Sample of mixture is placed just past one end of the chromatography surface (usually paper) End with sample is placed in another liquid (solvent) Chromatography Solvent is absorbed and travels up surface with mixture Different components of mixture travel different lengths up the surface 8