Lecture 1 - LECTURE 1 Chapters 1: Chemical Measurements...

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Anal Chem 251 Lect 1 1 LECTURE 1 Chapters 1: Chemical Measurements Chapter 2: Tools of the Trade Chapter 3: Math Tool Kit Chapter 4: Statistics
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Anal Chem 251 Lect 1 2 Analytical Chemistry Scientists from different fields use analytical chemistry Qualitative Analysis: Identifying what is in an unknown Quantitative Analysis: Identifying how much is present
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Anal Chem 251 Lect 1 3 General Steps in a Chemical Analysis • Formulating the question • Selecting analytical procedures • Sampling • Sample Preparation • Analysis • Reporting and interpretation • Drawing conclusions
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Anal Chem 251 Lect 1 4 CHAPTER 1 – CHEMICAL MEASUREMENTS
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Anal Chem 251 Lect 1 5
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Anal Chem 251 Lect 1 6
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Anal Chem 251 Lect 1 7
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Anal Chem 251 Lect 1 8 In 1999, the $125 million Mars Climate Orbiter spacecraft was lost when it entered the Martian atmosphere 100 km lower than planned because of an error in units.
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Anal Chem 251 Lect 1 9 Review- Chemical Concentrations • Solute : minor species in a solution • Solvent : major species in a solution • Concentration : how much solute is contained in a given volume or mass • Molarity : is the number of moles of a solute per liter of solution • Moles : grams per molar mass
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Anal Chem 251 Lect 1 10 Percent Composition Mass fraction = mass of solute/mass of total solution or mixture mass percent = mass fraction x 100 ppt = parts per thousand = mass fraction x 1000 ppm = parts per million = mass fraction x 10 6 ppb = parts per billion = mass fraction x 10 9 The density of a dilute aqueous solution is close to 1 g/mL so we equate 1 gram of a dilute solution to 1 mL of solution 1ppm =1μg/10 6 μg = 1μg/1g ~ 1μg/mL • 1μg/1mL x1000/1000 = 1000 μg/1000 mL = 1mg/1L 1ppb = 1ng/10 9 ng = 1ng/1g ~ 1ng/1mL • 1ng/1mL x 1000/1000 = 1000 ng/1000mL = 1μg/1L 1ppm or 1μg/1g ~ 1μg/mL ~ 1mg/L for dilute solus where d is close to 1 g/mL 1ppb or 1ng/g ~ 1ng/mL ~ 1μg/L for dilute solus where d is close to 1 g/mL
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Anal Chem 251 Lect 1 11 Converting wt % to molarity Problem : Find the molarity of a 37.0% HCl solution that has a density of 1.188 g/mL. Step 1 : Convert weight percent to g of HCl/L of solu via density 37.0 g HCL/100 g of solu x 1.188 g solu/1mL of solu x 1000 mL/1L = 439.6 g HCL/L of solu Step 2 : Convert g of HCl/L of solu to moles of HCl per L of solu (Molarity) 439.6 g HCl/L of solu x 1mol HCl/36.46 g = 12.1 mol/L = 12.1 M
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Anal Chem 251 Lect 1 12 Converting ppb to Molarity Problem: The concentration of compound A in seawater is 34 ppb. Find the molarity of this compound? The molar mass of A is 408.8 g/mol. We know: ppb = parts per billion = mass fraction x 10 9 1ppb = 1ng/10 9 ng = 1ng/1g ~ 1ng/1mL (for a dilute solu) 34 ppb = 34 ng/mL (for a dilute solution) Step 1 : Convert ppb to g/L 34 ng/mL x 10 -9 g/ng x 1000 mL/L = 34 x 10 -6 g/L Step 2 : Convert g/L to molarity 34 x 10 -6 g/L x 1 mol/408.8 g = 8.3 x10 -8 M
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Anal Chem 251 Lect 1 13 Preparation of Solutions Problem : The molarity of purchased concentrated HCl is 12.1 M.
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Lecture 1 - LECTURE 1 Chapters 1: Chemical Measurements...

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