Lab Essays - Christina Wong AP Chemistry 4th Hour 5/05/2010...

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Christina Wong AP Chemistry 4 th Hour 5/05/2010 Review for AP Exam – Lab Essays 1. Describe a procedure including equipment, measurements, and calculations needed to determine the rate law for the following reaction. S 2 O 3 2- + 2 H 3 O + S + SO 2 + 3 H 2 O You are given a 0.15 M solution of Na 2 S 2 O 3 and a 6.0 M solution of HCl. The main purpose of this lab was to determine the rate law of this reaction by using a well plate, a few Beral pipets, a stopwatch, beakers, and the solutions. We would also have to find some method of doubling the concentration of Na 2 S 2 O 3 and halving the concentration of HCl. With that, Na 2 S 2 O 3 can be mixed with HCl, and then a stopwatch can be used to determine how long they take to react together, which can be observed in a color change. Two other reactions besides the 0.15 M solution and the 6.0 M solution must be observed: the 0.30 M solution and the 6.0 M solution, and the 0.15 M solution and 3.0 M solution. If the time that the reaction takes is halved when the concentration of Na 2 S 2 O 3 is doubled, then the reaction is first order in it. If it is cut to a fourth, then the reaction is second order in it. The same logic applies to HCl – when its concentration is halved, if the time for the reaction is doubled, then the reaction is first order in it. We can conclude from this what the order of each of the two reactants is. The rate expression is Rate = k[S 2 O 3 2- ] x [H 3 O + ] y , where x and y are the two orders determined. To determine the k or the rate we can use the equation k = Ae -Ea/RT or the Arrhenius equation. 2. Iron forms ions with two different oxidation states: Fe 2+ and Fe 3+ Copper also forms ions with two different oxidation states: Cu 2+ and Cu 3+ Solid iron metal and an aqueous solution of a copper compound react to form copper metal and an aqueous solution of copper compound react to form copper metal and an aqueous solution of an iron compound according to the following reaction: Fe (s) + Cu 2+ (aq) Fe 2+ (aq) + Cu(s) Describe a procedure including equipment, measurements, and calculations needed to determine the oxidation state of the copper ion and of the iron ion formed.
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Metallic iron, solid copper (?) chloride, and deionized water are available. In this lab, we use the process of electrochemistry by placing the copper cathode in one half cells and placing the iron anode in the other half cell to determine the oxidation states. The equipment needed to determine the oxidation state of the copper and iron ions formed include the well plate, salt bridge, copper and iron pieces, a copper and iron solution, graduated cylinder, wires and clips, test tubes, steel wool, a voltmeter, and a few Beral pipets. In each half cell, there should be deionized water present in order to have the reaction go forward. We would have to measure the voltage difference between the two cells by using the voltmeter. Then we could use the Nernst equation or E = E - RT/ ̊ nF (lnQ). We can plug in all the values and determine the n or the number of moles in
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Lab Essays - Christina Wong AP Chemistry 4th Hour 5/05/2010...

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