lab essays

# lab essays - Ke Li 4 hour 5/8/08 th Lab Essays 1. Given...

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Ke Li 4 th hour 5/8/08 Lab Essays 1. Given 0.15M Na 2 S 2 O 3 and 6.0M HCl, determine the rate law for this reaction: S 2 O 3 2- + 2H 3 O + S + SO 2 + 3H 2 O Determine the mass and volume of a drop of water like. Prepare 3 reaction wells. In reaction well #1, add 2 drops 0.15 M Na 2 S 2 O 3 solution, 2 drops 6.0 M HCl solution, 5 drops water, and 1 drop indicator. Time the reaction (using a stopwatch) from when you add the HCl to when color changes, and record the time in a table. Run reaction #2 with 4 drops 0.15 M Na 2 S 2 O 3 solution, 2 drops 6.0 M HCl solution, 3 drops water, and 1 drop indicator solution. Time this reaction. Run reaction #3with 2 drops 0.15 M Na 2 S 2 O 3 solution, 4 drops 6.0 M HCl solution, 3 drops water, and 1 drop indicator solution. Time this reaction. For accuracy, it may help to take the average times from several sets of data. The rate law can be expressed as Rate = k[S 2 O 3 2- ] m [H + ] n Find the initial concentration of each reactant in each well. Then divide concentration by seconds to find rate. You divide Rate 2 by Rate 1 . Rate 2 = k[S 2 O 3 2- ] x [H + ] y = [S 2 O 3 2- ] x Rate 1 k[S 2 O 3 2- ] x [H + ] y [S 2 O 3 2- ] x By substituting in appropriate numbers collected as data, x can be found. Similarly, if you divide Rate 3 by Rate 1 , you can find y. These are then substituted into the rate law for any of the reactions to find the rate constant k. 2. Redox titration: Given metallic iron, solid copper chloride, and deionized water, determine the concentration of the copper ion and of the iron ion formed in this reaction. Fe (s) + Cu ?+ (aq) Fe ?+ (aq) + Cu (s) Since this is a redox reaction, set up an electrolytic cell in a beaker. Iron gets oxidized here so it is the cathode, while copper is the anode. Attach the battery cathode and anode accordingly. If you know the output of the battery in amperes, you can convert amperes to moles electron using Amps = 1 C * 1 mole e - 1 s 96500 C Once this is calculated, you can use stoichiometry with the knowledge the oxidation states here to calculate how many moles of iron and copper. With this knowledge, you divide the number of moles of copper ion and iron ion by total volume for concentration. 3. Determine the number of water molecules in a hydrated crystal CuSO 4 ∙?H 2 O Mass a small amount of CuSO 4 ∙?H 2 O on a scale then pulverize it with a mortar and pestle. Put the powder in a crucible. Hold the crucible with tongs above a Bunsen burner until the water has evaporated. After all the water has been driven off, mass the remains on a scale. Calculate the number of moles of CuSO 4 left. Take the difference of the two masses to find the mass of the water driven off. Divide the mass of the water driven off

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by the molar mass of H 2 O, 18.02 g, to find the moles of water. Then, divide the moles water by the number of moles of CuSO 4 . This gives the number of water molecules in each hydrated crystal. 4. A solution containing any or all of the following cations is to be analyzed. Ag
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## This note was uploaded on 05/25/2010 for the course CHEM 101 taught by Professor Fricke during the Spring '10 term at Canisius College.

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lab essays - Ke Li 4 hour 5/8/08 th Lab Essays 1. Given...

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