Analytical Chemistry potx

1 Analytical Chemistry Week 4 ENVI 15 - Analytical Chemistry Lecture 2 Last Week We Discussed Measurement Uncertainty -Systematic and random error -Accuracy vs precision -Significant figures -Average and standard deviations Quality Assurance/Quality Control (QA/QC) Review Harris Chapter 5 ENVI 15 - Analytical Chemistry Lecture 2 Quality Assurance  A program to produce high quality data with known uncertainty. 2 ENVI 15 - Analytical Chemistry Lecture 2 Quality Assurance  Elements of a QA program are:  Quality Control  Quality Assessment  An accredited laboratory has a well- developed QA/QC program  ISO 17025 – Industry Standard ENVI 15 - Analytical Chemistry Lecture 2 Quality Assurance  Quality Control  Establish Method Detection and Reporting Limits  Reagent Blanks  Calibration standards  Analysis of standard reference materials  Analysis of duplicates  Recovery of known additions (spikes)  Control Charts  Analyst proficiency checks ENVI 15 - Analytical Chemistry Lecture 2 Quality Assurance  Quality Assessment  Performance Evaluation Samples  Laboratory Round Robins  Performance Audits Analytical Chemistry Concentration Concepts Harris Chapter 1 3 ENVI 15 - Analytical Chemistry Lecture 2 Atomic Mass  Atomic mass of element = mass of one atom of that element  (a really, really small number!!) ENVI 15 - Analytical Chemistry Lecture 2 Molecular Mass  Molecular mass of a molecule = mass of one molecule  (which is the sum of the atomic masses that make up the molecule)  (still a really, really small number!!) ENVI 15 - Analytical Chemistry Lecture 2 The MOLE  A Mole is Avogadro’s Number (6.022 x 10 23 ) of atoms or molecules ENVI 15 - Analytical Chemistry Lecture 2 The MOLE Concept NaCl NaCl NaCl NaCl NaClNaCl NaCl NaCl NaCl NaCl NaCl NaClNaCl NaCl 4 ENVI 15 - Analytical Chemistry Lecture 2 The MOLE  Atomic mass X 1 mole of atoms = Atomic mass in grams  e.g. Na (22.98 amu) X 1 mole = 22.98 g ENVI 15 - Analytical Chemistry Lecture 2 The MOLE  Molecular mass X 1 mole of molecules= Molecular mass in grams  Na(22.99) + Cl (35.45) x 1 mol = 58.44 g ENVI 15 - Analytical Chemistry Lecture 2 Find the Molecular Mass  BaCl 2  H 2 SO 4  Hg 2 (NO 3 ) 2 Ba = 137.327 g/mol H = 1.008 g/mol Cl = 35.453 g/mol S = 32.062 g/mol O = 15.999 g/mol Hg = 200.59 g/mol N = 14.007 g/mol ENVI 15 - Analytical Chemistry Lecture 2 Solutions  What happens when we put a small amount of NaCl in water?  Solute and solvent 5 ENVI 15 - Analytical Chemistry Lecture 2 Concentration  Refers to how much solute is in a given volume or mass of solvent.  Standard concentration measure in chemistry is: # of moles / L  We call this molarity (M for short)  [Compound] = concentration of compound ENVI 15 - Analytical Chemistry Lecture 2 Molarity of Sea Salts  What is the molarity of NaCl in seawater if it contains 2.7 g NaCl per 100 mL?  The molecular mass of NaCl is 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol  # of moles of NaCl = 2.7 g = 0.046 mol 58.44 g /mol ENVI 15 - Analytical Chemistry Lecture 2 Molarity of Sea Salts  What is the molarity of NaCl in seawater if it contains 2.7 g NaCl per 100 mL? The molecular mass of NaCl is 22.99 (Na) + 35.45 (Cl) = 58.44 g/mol # of moles of NaCl = 2.7 g = 0.046 mol 58.44 g /mol 100 mL = 0.100 L [NaCl] = mol NaCl = 0.046 mol = 0.46 mol/L or M L 0. 100 L ENVI 15 - Analytical Chemistry Lecture 2 6 ENVI 15 - Analytical Chemistry Lecture 2 Molarity of Sea Salts [NaCl] = mol NaCl = 0.046 mol = 0.46 mol/L L 0. 100 L How many millimoles of NaCl in 1 L of seawater? How many micromoles? ENVI 15 - Analytical Chemistry Lecture 2 ENVI 15 - Analytical Chemistry Lecture 2 Concentration  Other measures of concentration are:  g/L, mg/L, µg/L, ng/L etc  g/kg  wt%  Vol%  Parts per … ppm, ppb, ppt etc ENVI 15 - Analytical Chemistry Lecture 2 Mass Concentration  What is the NaCl concentration (in mg/L) in seawater if it contains 2.7 g of NaCl per 100 mL?  [NaCl] = 2.7 g we want answer in mg/L NaCl (mg/L) = 2.7 g x 1000 mg x 1000 mL 100 mL 100 mL 1 g 1 L = 2700 mg/L 7 ENVI 15 - Analytical Chemistry Lecture 2 Percent Concentration  Weight percent (w/w) = weight solute/weight solution x 100%  Volume percent (v/v) = volume solute/volume solution x 100%  Weight/volume (w/v) = weight solute, g/volume solution, mL x 100% ENVI 15 - Analytical Chemistry Lecture 2 Percent Concentration  For %w/w and %vol/vol, the units must be the same  A 10% (vol/vol) solution is prepared by dissolving 10 mL of a pure substance in the amount of solvent it takes to produce a 100 mL solution  Best done with a volumetric flask ENVI 15 - Analytical Chemistry Lecture 2 Parts per Million and Parts per Billion  C ppm = mass solute/mass solution x 10 6  C ppb = mass solute/mass solution x 10 9 Note units in numerator and denominator must agree ENVI 15 - Analytical Chemistry Lecture 2 Parts per Million and Parts per Billion  C ppm = mass solute/mass solution x 10 6  C ppb = mass solute/mass solution x 10 9  What is parts per trillion? 8 ENVI 15 - Analytical Chemistry Lecture 2 Parts per Million and Parts per Billion  C ppm = mass solute/mass solution x 10 6  For aqueous solutions, 1 ppm = 1 mg/L  C ppb = mass solute/mass solution x 10 9  For aqueous solutions, 1 ppb = ? ENVI 15 - Analytical Chemistry Lecture 2 The Dilution Equation V 1 x C 1 = V 2 X C 2  Where:  V 1 is the initial volume  C 1 is the initial concentration  V 2 is the final volume  C 2 is the final concentration Lab Volumetric Glassware Calibrating Burets and Pipets ENVI 15 - Analytical Chemistry Lecture 2 Buret 9 ENVI 15 - Analytical Chemistry Lecture 2 ENVI 15 - Analytical Chemistry Lecture 2 ENVI 15 - Analytical Chemistry Lecture 2 Reading the Buret Estimate each reading to ±0.01 mL For example 13.63 mL ENVI 15 - Analytical Chemistry Lecture 2 10 ENVI 15 - Analytical Chemistry Lecture 2 ENVI 15 - Analytical Chemistry Lecture 2 Pipets TD or TC marks ENVI 15 - Analytical Chemistry Lecture 2 ENVI 15 - Analytical Chemistry Lecture 2 [...]...ENVI 15 - Analytical Chemistry Lecture 2 11 . 15 - Analytical Chemistry Lecture 2 Buret 9 ENVI 15 - Analytical Chemistry Lecture 2 ENVI 15 - Analytical Chemistry Lecture 2 ENVI 15 - Analytical Chemistry. example 13.63 mL ENVI 15 - Analytical Chemistry Lecture 2 10 ENVI 15 - Analytical Chemistry Lecture 2 ENVI 15 - Analytical Chemistry Lecture 2 Pipets TD