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Chemistry Lab Report Essay Sample

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  • Pages: 5
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Introduction of TOPIC

Sample Calculations:
Moles of oxalate pipetted:
10.00 mL = 0.0100 L
0.0100 L x 6.82 x 10-2 mol L-1
= 6.82 x 10-4 mol

Moles of permanganate needed:
10.90 mL = .01090 L
.01090 L x 0.025 mol L-1
= 2.725 x 10-4 mol

Smallest integer oxalate to permanganate mole ratio:
6.82 x 10-4 mol = 5
2.725 x 10-4 mol 2

Balanced reaction between oxalate and permanganate:
5 C2O42- (aq) + 2 MnO4- (aq) + __ H+ (aq) –> 10 CO2 (g) + 2 Mn2+ (aq) + ____ H2O (l)

To figure out z, the coefficient in front of H+, you must simply balance the reaction. Since there are 28 oxygen molecules on the reactant side and only 20 on the product side, the coefficient in front of the H2O must be 8. This makes the number of hydrogen molecules equal to 16 on the product side, therefore the coefficient in front of the H+ must be 16. The balanced reaction is:

5 C2O42- (aq) + 2 MnO4- (aq) + 16 H+ (aq) –> 10 CO2 (g) + 2 Mn2+ (aq) + 8 H2O (l)

Part 2: The Co2+ catalyzed tartrate – hydrogen peroxide reaction
For the 1 mL reaction, the solution started out a light pink and then turned into a brown color with an orange tinge. At around 3 minutes the solution began bubbling and looked like ginger ale. Then, the solution turned yellowish and there was much more bubbling and fizzing at 4 minutes. The solution turned green around 5 minutes and then a deeper green at 6 minutes. The solution continued to fizz and bubbles gathered around the edges. At around 7 minutes you could begin to feel the solution getting much hotter because it was releasing heat. It also turned a very bright green. At 8 minutes and 30 seconds, the solution boiled, became cloudier and the bubbles moved to the surface. At 9 minutes it turned a very deep green with a blue tinge. By 10 minutes the fizzing slowed down and then eventually stopped.

For the 2 mL reaction, the bubbles were a much larger size. The bubbles rose and popped at the surface at 4 minutes. At 4 minutes and 30 seconds the solution turned muddier, yellow-green and then olive green. There was audible fizzing at 5 minutes and 40 seconds and the solution released heat at around 6 minutes. At 7 minutes the solution began boiling and then at 8 minutes the fizzing slowed down.

Questions:
1. What were the important procedural steps you followed in the titration part of today’s experiment? Describe briefly the procedure you followed, placing emphasis on the critical steps. Try to be succinct. After the Na2C2O4 was transferred from the vial to the beaker, extra care was taken to transfer every last milligram of the Na2C2O4 from the beaker to the Erlenmeyer flask. This was done so that the molarity of the solution would be accurate when calculating the number of moles of C2O4- was used. The beaker and the stirring rod used to homogenize the solution were all rinsed with water several times and the rinsings were poured into the Erlenmeyer flask. The b

uret was prepared by rinsing it with deionized water and then with the permanganate solution.

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style="text-align: justify;">Rinsing it with the permanganate is critical because that eliminates any deionized water droplets. 8 mL of the permanganate were poured into the Na2C2O4 solution before the solution was heated and stirred on a hot plate for a few minutes. This was done to catalyze the reaction. If this had not been done, then the reaction would have taken a much longer time to proceed because more activation energy would have been needed. Any droplets of the permanganate that were clinging to the side of the Erlenmeyer flask were rinsed into the solution. After the heating, the solution was titrated drop by drop. Titrating carefully is critical to the titration process because you must be within one-drop accuracy. The solution was titrated until it turned a very light pink color. It is also important to note that all of the equipment used in the experiment, including the beaker, the flask, the stirring rod, the buret, and the volumetric pipette, were all rinsed with deionized water several times before usage.

2. What were the important procedural steps you followed in part 2 of today’s experiment? Try to be succinct. 40 mL of 3% H2O2 and 5.004 g of tartrate salt were added to a beaker. Using a stirring rod, the salt was dissolved in the H2O2. 20 mL of the solution and 1.0 mL of 0.17 mol L-1 CoCl2 were transferred to a 50 mL beaker. Adding the CoCl2 is critical because it acts as a catalyst for the reaction. Immediately after the CoCl2 was added, the timer was started. Then, for the second portion of part 2, 2.0 mL of 0.17 mol L-1 CoCl2 were transferred to the remaining 20 mL of the tartrate solution. And once again, the timer was started immediately after the addition of CoCl2.

3. What were the experimentally determined values of the mole ratio between oxalate and permanganate titrations? Were they consistent? What did you deduce regarding the stoichiometry of the reaction between the two reactants? State the logic behind your deduction. Be succinct. All three of the experimentally determined values of the mole ratio between the oxalate and permanganate titrations were 5/2, so they were consistent with one another. The coefficients in front of the reactants were based off of this mole ratio. The mole ratio tells us how many moles of one reactant compared to another reactant are needed to complete a reaction.

4. What were your qualitative observations in part 2? Did runs 1 and 2 differ in any way? If yes, describe the differences. Be succinct. For the 1 mL reaction, the solution started out a light pink and then turned into a brown color with an orange tinge. At around 3 minutes the solution began bubbling and looked like ginger ale. The solution turned green at around 5 minutes and then a deeper green at 6 minutes. The solution continued to fizz and bubbles gathered around the edges. At around 7 minutes you could begin to feel the solution getting much hotter because it was releasing heat. It also turned a very bright green. At 8 minutes and 30 seconds, the solution boiled, became cloudier and the bubbles moved to the surface. By 10 minutes the fizzing slowed down and then eventually stopped.

For the 2 mL reaction, the bubbles were a much larger size. The bubbles rose and popped at the surface at 4 minutes. At 4 minutes and 30 seconds the solution turned muddier, yellow-green and then olive green. There was audible fizzing at 5 minutes and 40 seconds and the solution released heat at around 6 minutes. At 7 minutes the solution began boiling and then at 8 minutes the fizzing slowed down.

Runs 1 and 2 differ in that the reaction in run 2 occurred a little bit more rapidly than the reaction in run 1. In addition, the bubbles in run 2 were much larger.

5. What was/were the limiting factors/measurement(s) on the accuracy of the final result in part 1? What was/were the limiting factors/measurement(s) on the precision of the experiment? Were there any unreasonable assumptions in the procedure and/or logic? The accuracy of the final result was limited by the volume measurements. The buret and pipet were accurate to the hundredths place, and had 4 significant figures, so the accuracy of the final result was limited to 4 significant figures. The precision of the experiment was limited by the fact that the titrations were only conducted 3 times. If it had been conducted a greater number of times, the volume of permanganate required to titrate the Na2C2O4 solution would have been more accurate as well as precise. Some assumptions made in this experiment were that the reaction between the permanganate and Na2C2O4 occurs rapidly and completely. It was also assumed that there were no side reactions and that no indicator was needed to indicate the end of the titration. There is no evidence contradicting these assumptions.

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