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Prelab Components

# Prelab Components - EXPERIMENTS IN GENERAL CHEMISTRY...

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EXPERIMENTS IN GENERAL CHEMISTRY Additional Pre-Lab Components CHEM117 – Fall 2010

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1 Experiment 1: Measured properties are characterized by their accuracy and their precision. When using measured values in calculations, it is most important to note that precision can neither be gained nor lost. The rules for significant figures usually obey this principle, but sometimes the result has to be adjusted to maintain precision. Use the following example to illustrate these ideas: 1. A liquid was measured to occupy a volume of 4.8 mL using a graduated cylinder, and its mass was determined using balances of different precision: Triple-beam balance (precision of 1 dec. pl.): m = 5.3 g Analytical balance (precision of 3 dec. pl.): m = 5.261 g Show that both mass-measurements, combined with the volume measurement, yield the same value for the density of the liquid. 2. A high-density liquid (d = 2.32 g/cm 3 ) was measured to occupy a volume of 49.4 mL using a graduated cylinder. Report the mass of the liquid with correct precision. Is this result in accordance with the rules for significant figures? When measuring volumes, the correct reading of the meniscus is key to producing reliable results. Use the following example to illustrate this idea: 3. A liquid was measured to occupy a certain volume using a graduated cylinder, and its mass was determined using balances of different precision. Two experimenters report two different values for the density: Experimenter 1: m = 37.598 g (Analytical balance) d = 1.0 g/mL Experimenter 2: m = 37.6 g (Triple-beam balance) d = 1.1 g/mL Decide which experimenter reports a correct result, and explain where the other experimenter went wrong.
2 Experiment 2: The most general form of a chemical equation is reactants products. Most often, reactants and products are described by their chemical formula, possibly including a designation of state of matter. Contrary to a general chemical equation, a balanced chemical equation always uses molecular formulas and is amended by stoichiometric factors to assure conservation of mass and/or moles. Chemical equations represent chemical reactions, and chemical reactions can be classified according to two groups: Group I (bond breakage and/or bond formation): The four reaction types are Synthesis, Decomposition, Single Displacement, Double Displacement. Group II (common reaction principles): Representative examples are Precipitation, Redox, Acid-Base, Combustion. Choose from the following general chemical equations, and illustrate the four principle group I reaction types, and the four representative group II reaction types: A) aqueous potassium sulfate + aqueous barium nitrate aqueous potassium nitrate + solid barium sulfate B) magnesium metal + nitrogen gas solid magnesium nitride C) copper metal + aqueous silver nitrate aqueous copper nitrate + silver metal D) chlorine gas + fluorine gas chlorine monofluoride gas E) aqueous hydrochloric acid + aqueous calcium hydroxide aqueous calcium chloride + water F) gaseous sulfur dioxide + oxygen gas gaseous sulfur trioxide G) solid calcium carbonate

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