Lecture_overheads_-_Ch01

Lecture_overheads_-_Ch01 - CHEM 321 Quantitative Analysis...

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CHEM 321 – Quantitative Analysis Ch. 1 – Measurements This chapter is review of general chemistry concepts 1-1 SI Units Units Prefixes Converting between units 1-2 Chemical Concentrations Moles M, N, F wt%, ppm, ppb 1-3 Preparing Solutions 1-4 Stoichiometry Calculations for Gravimetric Analysis 1-5 Introduction to Titrations 1-6 Titration Calculations
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1-1 SI Units
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Using prefixes ( memorize this subset from Table 1-3) prefix symbol factor example mega M 10 6 1 Mg = 10 6 g kilo k 10 3 1 kg = 10 3 g milli m 10 -3 1 mg = 10 -3 g micro μ 10 -6 1 μ g = 10 -6 g nano n 10 -9 1 ng = 10 -9 g pico p 10 -12 1 pg = 10 -12 g To convert between units: Multiple by appropriate conversion factor (this is ratio that is equivalent to 1) Cancel out units (to confirm conversion to the desired units) Examples g 10 2.5 g 10 g 1 g 25 mL 12.0 L 1 mL 1000 L 0.0120 5 - 6 × = × = × μ
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To convert between units: MULTIPLY BY CONVERSION FACTOR (this is a RATIO that is equivalent to 1) CANCEL OUT UNITS (to confirm correct conversion) Examples atm 102.1 Pa 01325 1 atm 1 psi 1 Pa 6895 psi 1500 J 10 8.0 eV 1 J 10 1.6 keV 1 eV 1000 keV 50 m 10 1.00 L 1 m 10 mL 1000 L 1 mL 100 16 - 19 - 3 4 - 3 -3 = × × × = × × × × = × ×
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Challenge problems involving conversion between units: What is the wavelength in angstroms of a 20 keV photon? What is the mass in kg of one benzene molecule? What is the equivalent concentration of Na in units of μ g/mL of a seawater sample containing 2.7% NaCl (wt/wt)? What is the concentration in ppb of an air sample (STP) containing benzene at a concentration of 10 μ g/m 3 ?
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1-2 Chemical Concentrations Moles and mw’s 1 mole = Avogadro’s number = 6.022 x 10 23 atoms or molecules Convenient to express this extremely large number in units of moles mw or aw = mass of substance that is equivalent to 1 mole this is a RATIO expressed in g/mole mw of H 2 = 2 Da 2 g = 1 mole mw = 2 g/mole mw of NaCl = 58.44 Da 58.44 g = 1 mole mw = 58.44 g/mole mw of lyzozyme = 14,400 Da 14.4 kg = 1 mole mw = 14,400 g/mole Can use tabulated aw’s from the periodic table to compute mw of a substance and hence its number of moles Be careful to compute mw to correct number of significant figures Example Calculate the mw of NaCl note errors in aw’s in periodic table from text are accurate to ±1 in last digit MW NaCl = AW Na + AW Cl = 22.98976928 + 35.453 = 58.443 g NaCl / mol mw wt moles =
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Units of concentration Molarity (M) Normality (N) Chemical entity can be charge (+ or -), protons (H + ), electrons, etc Think of N = M * number of reacting units Example Calculate the N of a 0.1 M sulfuric acid solution based on the number of H + atoms Note this is a diprotic acid (K a2 = 1 x 10 -2 ) = = L mole Molarity M + + + = = = H N 0.2 L H mol 0.2 SO H mol H mol 2 L SO H mol 0.1 SO H M 0.1 4 2 4 2 4 2 = = = L s equivalent L entity" chemical " mole Normality N
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Lecture_overheads_-_Ch01 - CHEM 321 Quantitative Analysis...

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