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QCA7e_ch01_szb_handouts

QCA7e_ch01_szb_handouts - Daniel C Harris Quantitative...

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1 Quantitative Chemical Analysis Seventh Edition Quantitative Chemical Analysis Seventh Edition Chapter 1 Measurements Daniel C. Harris Daniel C. Harris Topics in this Chapter • units of measurement • chemical concentrations • preparation of solutions • stoichiometry of chemical reactions
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2 An Ultrasensitive Measurement Atomic absorption signal from 60 gaseous rubidium atoms observed by laser wave mixing. A 10-microliter (10 × 10 6 L) sample containing 1 attogram (1 × 10 18 g) of Rb + was injected into a graphite furnace to create the atomic vapor. Système International d'Unités
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3 Système International d'Unités Prefixes • Rather than using exponential notation, we often use prefixes to express large or small quantities.
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4 Use of prefixes At an altitude of 1.7 × 10 4 meters above the earth's surface, the pressure of ozone over Antarctica reaches a peak of 0.019 Pa. Let's express these numbers with prefixes: We customarily use prefixes for every third power of ten (10 9 , 10 6 , 10 3 , 10 3 , 10 6 , 10 9 , etc) The number 1.7 × l0 4 m is more than 10 3 m and less than 10 6 m, so we use a multiple of 10 3 m (= kilometers, km): Use of prefixes At an altitude of 1.7 × 10 4 meters above the earth's surface, the pressure of ozone over Antarctica reaches a peak of 0.019 Pa. Let's express these numbers with prefixes: We customarily use prefixes for every third power of ten (10 9 , 10 6 , 10 3 , 10 3 , 10 6 , 10 9 , etc) The number 0.019 Pa is more than 10 3 Pa and less than 100 Pa, so we use a multiple of 10 3 Pa (= millipascals, mPa):
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5 Example for conversions Express the rate of energy used by a person walking 2 miles per hour (91 Calories per hour per 100 pounds of body mass) in kilojoules per hour per kilogram of body mass. Solution: First, note that 91 Calories equals 91 kcal. Table 1-4 states that 1 cal = 4.184 J; so 1 kcal = 4.184 kJ, and Table 1-4 also says that 1 lb is 0.453 6 kg; so 100 lb = 45.36 kg. The rate of energy consumption is therefore We could have written this as one long calculation:
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6 Chemical Concentrations A solution is a homogeneous mixture of two or more substances. A minor species in a solution is called solute and the major species is the solvent. Most of our discussions concern aqueous solutions, in which the solvent is water. Concentration states how much solute is contained in a given volume or mass of solution or solvent. Molarity and Molality A mole (mol) is Avogadro's number of particles. Molarity (M) is the number of moles of a substance per liter of solution. A liter(L) is the volume of a cube that is 10 cm on each edge. Because 10 cm = 0.1 m, 1 L = (0.1 m) 3 = 10 3 m 3 . Chemical concentrations, denoted with square brackets, are usually expressed in moles per liter (M). Thus ”[H+]” means ”the concentration of H+.” Molality (m) is concentration expressed as moles of substance per kilogram of solvent.
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