JUN4 CHEM335101 METZ - lecture notes PDF

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Additional notes for the PowerPoint slides posted on canvas There are two types of chemical analysis 1. Qualitative: What’s in the solution? 2. Quantitative: How much? Most samples contain just two components  Analyte(s): the material you are trying to analyze  Matrix: everything else; irrelevant (usually) but sometimes can interfere with what you’re measuring Steps in analytical quantitation 1. – 2. Representative: sample should be taken out of homogeneous area (uniform). If it is in a heterogeneous area, then a problem arises because analytes isn’t uniform everywhere 3. – 4. – 5. – Using extraction to concentrate the analyte  Take sample that contains the analyte and put it in thimble. Put thimble in extractor. Put condenser on top and boiling solvent at bottom. Vapor rises and liquid drips down in thimble. Once liquid moves up into side arm, it’ll fall back into flask and keep boiling. The liquid is purer than before (distillation) Using extraction to concentrate the analyte  Put SPE at the end and squirt solution through cartilage and cartilage binds to molecules that is being squirted out. Then take extreme nonpolar solvent to flush out analyte Using extraction to concentrate the analyte  QuEChERS : standardized method The QuEChERS Method 1. – 2. Use acetonitrile: miscible with water. Dissolves completely. No layers formed. Also extract with opposite polarity. Miscible with other organic molecules. 3. Buffer’s pH: 7 4. – 5. – 6. – 7. – How could we quantify the amount of Na2CO3 in mix of Na2CO3 and SiO2?  Weigh powder directly  CO32= + 2H+  H2CO3 CO2 (g) + H2O (l)  Ideal gas law: PV=nRT  Calculate percentages  Titrations

Additional notes for the PowerPoint slides posted on canvas General Methods of Chemical Analysis  Classical: weight, titration (moles)  Instrumental From Handout: Molarity  Can be used for pure substances, too o Pure water  (Mol of H2O) / (Vol of H2O) or…  (Mol of H2O) / 1  so just weigh it and it is 55.5 mol  Q: 1 mol of NaCl and dissolve in water to make exactly 1 L total solution? o 0 Molar NaCl because dissolved in water o 1 Molar of sodium ion o 1 molar of chloride ion o So the correct way to say it is: 1 F NaCl Formality  How much you put of analyte in the beginning of the experiment. It is how much you begin with and you don’t care about what happens to it (ex: NaCl) during and after experiment  Not saying anything about the analyte dissolving or dissociating Normality  Ex: o 1 mol HCl produces 1 mol of H+  but this is a problem because it dissociates completely (so should think about formality) Weight  100x (g of analyte / total g of sample) = wt%  Ex: o Acetone and water miscible so you can express WT% by using g of acetone and water OR measure by volumes since they are liquids  [ (20 mL acetone) / (100 mL of total solution) ] x 100 = 20 % of volume OR 20 % v/v [in other words: (analyte)/ (total solution)] o Can also be in w/v or v/w Analysis of:  1000 g of total solution  0.04 g of Pb2+  100 x (0.04g/1000g)= 0.004 wt% (small number so instead of multiplying by 100, multiply with 1000 instead)  1000 x (0.04g/1000g)= 0.04 ppt  OR multiply by 106 40 ppm Dilutions  V1M1=V2M2 o EX:  V1: 100 mL  M1: 0.5 F  M2: 12 M (HCl)

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V2: ? (V2 tells you how much to dilute HCl)

Weighing Methods  W=mg  Weight is a force. Gravity is accounted.  Mass shouldn’t change from one place to another (Earth vs Moon)  The top left diagram with the unknown mass and known mass on a pivot is measuring mass  The other diagrams do not measure mass, but instead measure weight because they are taking account of gravity since gravity is pushing down on the bar or spring...