1 Dr. Anderson’s Favorite Uses for Diet Coke 1. Density Experiments 2. Diet Coke + Mentos Sticky Fun! http://www.eepybird.com/ CH204 Experiment 2 Dr. Brian Anderson Spring 2008 Experiment 1 PostGame Show pipette and burette intensive and extensive properties interpolation determining random experimental error What about gross error and systematic error?2 Experiment 1 PostGame Show continued... Another question: Isn’t there some error in the density we determined in Part 2? We going to Jamaica, mon! Separate a mixture of salt, sand, and chalk dust based on differences in their physical and chemical properties. Add water to dissolve NaCl. Add acid to dissolve CaCO 3 . SiO 2 is left behind in the beaker. Experiment 2 Overview Characteristics of a material that do not involve changing the chemical formula of the compound. Examples include: When a compound changes state (solid, liquid, gas, aqueous), it is still the same compound, so that’s a physical change, not a chemical change. Physical properties Boiling point Melting point Solubility Density Physical state Particle size Color Shape3 Characteristics of a material that DO require changing the chemical formula of the compound. This means reactivity with another chemical. Examples: • Flammability • Oxidizability (rust/tarnish/corrosion) • Oxidation/reduction in general • A host of other chemical reactions The products of a chemical process are different molecules than the reactants. Chemical properties Dissolve NaCl in water and recover NaCl by evaporating water. Is this process physical or chemical? React CaCO 3 with HCl to form CaCl 2 , then convert CaCl 2 to CaCO 3 by adding K 2 CO 3 . Physical or chemical? SiO 2 – insoluble in water, and unreactive to HCl. Physical or chemical? In this lab Part 1: Removal of NaCl Steps 35, transferring the dissolved NaCl: When you are rinsing the beaker with your squirt bottle, don’t use excessive amounts of water because you will have to evaporate it all away later.4 Separating the salt Step 4: pour the dissolved NaCl through a funnel lined with filter paper. Not all of the liquid will pour through the funnel – the final mL or so will refuse to drip through. Part 2: “Tiny Bubbles...!” Add HCl dropwise into the stirring mixture of sand and chalk to dissolve the chalk: CaCO 3 (s) + HCl(aq) CaCl 2 (aq) + H 2 O(l) + CO 2 (g) Tiny bubbles from the bottom of the beaker = chemical reaction “I can’t decant.” Don’t worry about a few grains of sand. “Remove the beaker from the hot plate and let it cool to room temperature.” Please DO NOT put hot items on the white lab bench surface!5 Part 3: Recovering the CaCO 3 Suction filtering is the trickiest part of the whole experiment. Did he say “Byookner?” Nein, Ich sprach “Büchner.” Büchner flask Büchner funnel Rübber hose wasser Filter paper Plastic connector Almost finished Biggest source of error – wet CaCO 3 Dry it as best you can in the Büchner funnel, then transfer it to an evaporating dish and dry it on the hot plate. Evaporate NaCl slowly in the large evaporating dish. Turn down the heat when the water level gets low. Dry the SiO 2 in the beaker.6 And when you’re done... Enter your name into the spreadsheet. Enter your starting mass and the final masses of the recovered NaCl, CaCO 3 , and SiO 2 . Do you feel lucky? For each component, you have the option of reporting your own data or the average results of everyone who had the same unknown as you. You can QTest outlying data points, but you cannot arbitrarily keep or reject data based on hunches, Tarot deck readings, or having “a really bad feeling about this one.” How’s that Qtest work again? Let’s go see. Remember, the Qtest is only used for discarding outliers in replicate analyses. (That means repeat measurements of the same thing.)7 Unknown Summary Sheets Some of the experiments we do will require you to identify a chemical unknown in some way : v Determine the identity of the unknown or v Determine its concentration or v Determine its composition In addition to your normal lab report, you will turn in an Unknown Summary Sheet for these experiments. Unknown Summary Sheets can be found on the small wooden shelves next to the stockroom or can be downloaded from the class web site at http://courses.cm.utexas.edu/banderson/ch204/uss.html Lab writeup Don’t forget to show a sample calculation for % recovery and for % of each component If you Qtest an outlying data point, show the calculation regardless of whether the point stays or goes. Postlab problem 2 Directly analogous to our experiment with NaCl, CaCO 3 , and SiO 2 . How would you separate and recover SiO 2 from NaCl and CaCO 3 ? Which of the separation and recovery techniques are physical and which are chemical?8 Preliminary Writeup for Experiment 3 When you copy the reaction tables on pages 21 and 22 Make them big! You will be writing your observations in those tiny boxes. Final exam time Quizzes make up 30% of your course grade. Nine quizzes, drop the lowest one. Each individual quiz you keep is worth about 3.75% of your final
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