Lec_03 - Today 1 Report for Experiment 1 is due(40 pts 2...

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Unformatted text preview: Today 1. Report for Experiment 1 is due (40 pts) 2. Post-lab for Experiment 1 is due (10 pts) 3. Pre-lab for Experiment 2 is due (5 pts) 4. Experiment 2. Separation and Recovery of the Components of the Mixture have a write-up in your notebook Next week 1. Report for Experiment 2 is due (40 pts) 2. Post-lab for Experiment 2 is due (10 pts) 3. Unknown Summary Sheet for Experiment 2 is due (20 pts) 4. Pre-lab for Experiment 3 is due (5 pts) 5. Experiment 3. Qualitative Chemical Analysis have a write-up in your notebook Spring 2007 Experiment 2. Separation and Recovery of the Components of a Mixture PURPOSE AND LEARNING OBJECTIVES To become familiar with the concept of quantitative analysis To separate and quantitatively recover the components of a mixture of sodium chloride, silicon dioxide, and calcium carbonate To become familiar with common laboratory techniques (filtration, decanting, evaporation, stirring, etc.) Quantitative Analysis focuses on determination of the amounts of the material (substance) of interest NaCl sodium chloride SiO2 silicon dioxide CaCO3 calcium carbonate Spring 2007 Separation/Purification and Recovery in Chemical Applications Physical Methods: make use of the differences in the physical properties of the components of the mixture, such as: Solubility Boiling point Melting point Particle size Chemical Methods: make use of selective reactivity of the components of the mixture towards certain chemical reagents Spring 2007 Physical and Chemical Properties of the Components of the Mixture Substance NaCl SiO2 CaCO3 Solubility in H2O yes no no Reactivity towards HCl no no yes Spring 2007 Step 1. Separating NaCl from a ThreeThree-Component Mixture NaCl (s) SiO2 (s) CaCO3 (s) H2O NaCl (aq) SiO2 (s) CaCO3 (s) Filtration Filtrate NaCl (aq) Evaporation NaCl (s) Residue SiO2 (s) CaCO3 (s) Spring 2007 Step 2. Separating SiO2 and CaCO3. Recovering SiO2 SiO2 (s) CaCO3 (s) HCl SiO2 (s) CaCl2 (aq) Decanting Liquid CaCl2 (aq) Residue SiO2 (s) CaCO3 (s) + 2 HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l) Spring 2007 Step 3. Recovering CaCO3 CaCl2 (aq) K2CO3 CaCO3 (s) + KCl (aq) Filtration Filtrate KCl (aq) Residue CaCO3 (s) CaCl2 (aq) + K2CO3 (aq) CaCO3 (s) + 2 KCl (aq) OR Ca2+ (aq) + CO32 (aq) CaCO3 (s) Spring 2007 Reporting your Data Report either your own results or the average values derived from the joint effort of a group of students including yourself You can mix and match You cannot report somebody else's data Spring 2007 Outliers Q test helps you to decide whether to retain or reject a questionable point within a given set of data (see Appendix 1 for details) Q calculated = gap range gap = | xsuspect xnear | range = xmax xmin Compare Qcalculated to Qtable: If Qcalculated > Qtable, the questionable point should be rejected. If Qcalculated < Qtable, the questionable point should be retained. Spring 2007 Example Measurement # 1 2 4.128 3 4.011 4 4.009 5 4.015 Mass of a sample (g) 4.012 gap range Q calculated = gap = | xsuspect xnear | range = xmax xmin xsuspect = 4.128 xmin = 4.009 xmax = 4.128 xnear = 4.015 gap = | 4.128 4.015 | = 0.113 range = 4.128 4.009 = 0.119 0.113 = 0.95 0.119 Qtable = 0.64 Q calculated = Qcalculated = 0.95 > Qtable = 0.64 xsuspect = 4.128 can be rejected Spring 2007 Equipment and Techniques: Heating and Mixing Hotplate/Stirrer Magnetic Stirring Bar Retriever Magnetic Stirring Bar Center the beaker on top of the hot/stir plate and start the magnetic stirrer on a low rotational speed Move the beaker around until you stabilize the stirring bar inside the solution and it starts spinning quietly in the middle of the beaker Stirring speed regulating knob Heat regulating knob Increase the rotational speed, so that a small swirl is formed inside the beaker Spring 2007 Equipment and Techniques: Gravity Filtration Vacuum Filtration Buchner funnel To the aspirator (vacuum) Filter flask Swirl the mixture as you pour Wash the reaction beaker with several portions of H2O to transfer any remaining solid from the beaker into the funnel Spring 2007 Equipment and Techniques: Miscellaneous Tips Never return unused portions of chemicals to the reagent bottle Whenever you remove an object (e.g. thermometer, stirring bar retriever, magnetic stirring bar, etc.) from the solution, make sure you rinse it off into your solution with the small amount of deionized water. This will insure that you do not lose any of your material Do not place hot objects directly onto the bench top, use the wire gauze to protect the bench top Teflon covers DO NOT throw out your residues until the end of the laboratory period Spring 2007 ...
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