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WKU CHEM 116 - Exam 1 Study Guide

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CHEM 116 1st EditionExam # 1 Study Guide Lectures: 1 - 4Lecture 1 (January 27)Scientific Method1. Observation or Experiment2. Develop a hypothesis3. RepeatExperiment (Observation): to monitor change in variables in a systematic way and look for rational conclusionsExplanation: predict the results of experiments; use mathematical or conceptual descriptions of natureLaw: expression of a fundamental relationship in nature and is an unequivocal truth (not often debated)Hypothesis: an educated guess; can be right or wrong but must be tested with experimentsTheory: a well-tested hypothesis; can be adjustedLaw of Conservation of MassMass is conserved during a chemical process (not created or destroyed). Mass is even conserved when the chemical identity changes.Mass: the quantity of matter in a material objectMatter: anything that occupies space and has massChemical Reaction: a change in the identity of matterExample. You heat 2.53g of metallic mercury in air, which produces 2.73g of a red-orange residue. Assume that the chemical change is the reaction of the metal with oxygen in the air. mercury + oxygen−−→red-orange residuea. What is the mass of oxygen that reacts? Mmercury = 2.53gMresidue = 2.73g Mercury + oxygen = red-orange residueMmercury + Moxygen = Mresidue so…. 2.53 + Moxygen = 2.73Moxygen = 2.73 – 2.53 = 0.20gb. When you strongly heat the red-orange residue it decomposes back to the mercury and releases the oxygen, which you collect. What is the mass of the oxygen you collect?The mass of the oxygen must stay the same because “it cannot be created or destroyed”Classifying MatterPhysical States: the form or phase which matter is classified intoSolid: rigid form of matter that has a fixed volume and fixed shapeFluid: non-rigid forms of matter that can flow and change shapeLiquid: incompressible fluid with a fixed volume but no fixed shapeGas: compressible fluid that has no fixed volume or fixed shapeAqueous: form of matter where a substance is dissolved in liquid waterPhysical Changes vs. Chemical ChangesPhysical Changes: alter the form of matter but not its identity -changing state (solid, liquid, gas)-dissolving sugar into water-physical properties include: phase change, color, temperature, density, massChemical Changes: reactions that alter the identity of matter-iron+oxygen+humidity=rust-chemical properties include: something rusting or burning in oxygenExample. Potassium is a soft, silvery-colored metal that melts at 64◦C. It reacts vigorously with water, with oxygen, and with chlorine. Identify all of the physical properties given in this description. Identify all of the chemical properties given.Phys: soft, silver, meltsChem: reactsChemical ConstitutionMixture: can be separated by a physical process- Homogeneous (solution)—a mixture with uniform properties- Heterogeneous—a mixture with physically distinct parts, each with different propertiesPure Substance: cannot be separated by a physical process- Element—cannot be chemically decomposed- Compound—can be chemically decomposed into elementsLaw of Definite ProportionsA pure compound always contains definite/constant proportions of elements by mass.Example. 1.0g of sodium chloride (NaCl) always contains 0.4g of sodium (Na) and 0.6g of chlorine (Cl). How many grams of Na and Cl are in 10g of NaCl?Due to the Law of Definite Proportions, there will always be .4g of Na and .6g of Cl.Lecture 2 (January 29)Physical Measurements Measurement:- Precision- the closeness of measured values within a set of identical measurements- Accuracy- closeness of a measured value to the “true” valueo The last digit is an estimate (9.12—2 is estimated)Know how to count significant figuresExample. Counting significant digits. Count the number of significant digits in the following numbers.- a. 76.870 – 5 - b. 0.085050 - 5- c. 579.5 - 4- d. 0.283258 - 6- e. 0.0000788 - 3- f. 10.000 - 5- g. 0.941084 - 6- h. 900 – ambiguous Know how to write in scientific notationExample. Expressing numbers in scientific notation. Write the following numbers in scientific notation.- a. 843.4 = 8.434 x 10˄2- b. 0.00421 = 4.21 x 10˄-3- c. 1.54 = 1.54 x 10˄0- d. 4.38 = 4.38 x 10˄0- e. 4380. = 4.380 x 10˄3- f. 0.000438 = 4.38 x 10˄-4- Also be able to go the other directionKnow how to add and subtract in scientific notation 9.42×10−2 + 7.6×10−3=9.42x10˄-2 + .76x10˄-2=10.18x10˄-2=1.018x10˄-1Know how to multiply and divide in Scientific Notationo When multiplying, add exponentso When dividing, subtract exponentso When taking a power to a power, multiply the exponents 6.4×102 / 2.0×105 (6.3×102)×(2.4×105)(6.3x2.4) x 10˄2+515x10˄71.5x10˄8Lecture 3 (February 3)Uncertain DigitsUncertain Digits: 1 digit past the last significant figure Example. Express in 3 sig. figs. - 1.2551 – 1.22- 1.2143 – 1.21 - 1.4972 – 1.50*Calculated results cannot be more “precise” than the measurements1. Mult/Div: keep least # of sig figs2. Add/Sub: keep least # of decimal places3. Do not take into account exact numbersExample. Using significant figures in calculations. Perform the following calculations and round the answers to the correct number of significant figures.- 2.568×5.8 ÷ 4.186 (fewest # of sig figs is 2 in 5.8, so final answer is limited to 2 sig figs) = 3.558146202 = 3.6- 5.41−0.398 (fewest decimal place is 2, so final answer is limited to 2 decimal places or thousandth place) = 5.012 = 5.01- 3.38−3.01 (2 decimal places) = 0.37- 4.18−58.16 × (3.38−3.01) (2 sig figs) = -175.41 + 0.0000001 = 5.41- do parentheses first- Multiplication is next, but the answer can only have 2 sig figs because .037 has 2)-keep track of sig figs as you go and use the rules as you goExample. Give answers to the following arithmetic. Round to the correct number of significant figures.- 5.61×7.891÷ 9.1(2 sig figs) = 4.894671429 = 4.9- 8.91−6.435 - 6.81−6.730 (2 decimal places) = 0.08- 38.91×(6.81−6.730) = 38.91 x .08 (subtracting limits to 2 decimal places)(multiplying limits to 1 sig fig) = 3.1128 = 3Example. You count that there are 9 identical coins in a bottle. The mass of that type of coin is 3.0g. What is the total mass of all the coins in the bottle?9 (3.0) = 27.0 g = 27SI Units: metric system, based on factors of 1Base Units- Length – Meter – m - Mass – Kilogram – kg - Time – Second – s - Temperature – Kelvin – K - Amount of Substance – Mole – mol SI Prefixes:


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