February 8 - February 11, 2010
Preliminary Reports are due this week.
This week you will analyze oxalate content (experiment 15-015) of your coordination compound during the lab period.
The water determination is done by gravimetric analysis. Last week you placed two samples in the lab drying ovens and allowed them to dry at 100 oC for one week. You will remove the samples from the drying ovens, cool them in a dessicator and weigh them.
The
oxalate determination will be done by titration with a
standardized permanganate solution. The experiment is divided
into two parts:
1. Determination of [MnO4-] of the standard KMnO4 solution.
You will make a standard solution of sodium oxalate and then titrate a sample of this solution with a dilute permanganate solution by two different methods. Using the known concentration of the sodium oxalate solution and the stoichiometry of reaction 1, you can determine the concentration of the KMnO4- solution. The titration should be repeated at least two times. Once this is done you can proceed to step 2.
2. Determination of the oxalate content of your coordination compound.
You will use the standardized KMnO4 solution to determine the oxalate concentration of your transition metal compound. You will weigh out some of your sample, dissolve it in water and titrate with the KMnO4 solution to the endpoint. You should repeat this titration at least 3 times. You will then be able to determine the moles of oxalate in your compound using the stoichiometry of reaction 1. Once moles are determined you can determine the mass and thus percentage of oxalate in your titration sample.
Calculations For Experiments 14 and 15:
Experiment 14-067: Determination of water content of your coordination compound
((Mass of sample before heating - Mass of sample after heating)/Mass of sample before heating) x 100% will give the water content of your sample. Does this compare favorably with the water content of potassium trisoxalatoferrate(III) trihydrate ?
Experiment 15-015: Determination of oxalate content of your coordination compound:
Determine the molarity of the standard Na2C2O4 solution. Determine the moles of C2O42- in each tiration (you should have used 5.00 mL (0.005 L) aliquots for each titration).
Using the stoichiometry of reaction 1, you can then determine the moles of MnO4- that were used to titrate the C2O42- (moles MnO4- = 2/5 moles C2O42-). To determine the molarity of the permanganate solution you should use the moles of MnO4- and the titration volumes you obtained using the Fowler-Bright method. Calculate the average permanganate concentration and use this concentration for the next set of calculations.
Use the average concentration of MnO4- and the titration volumes obtained from the titrations of your transition metal compound to determine moles MnO4- used in each titration. Once again use the stoichiometry of reaction 1, determine moles of C2O42- titrated (C2O42- = 5/2 moles of MnO4- ).
Convert moles C2O42- to grams of C2O42- titrated by using MW of C2O42-.
To find % C2O42- in your sample, (g C2O42- /g sample titrated) x 100%. Does this compare favorably with the oxalate content of potassium trisoxalatoferrate(III) trihydrate ?
Final Report (experiments 12 - 15) is due the week of February 22, 2010.
You should review the guidelines for writing a scientific report (manual, p. 40) and read the General Comments on the Final Report (manual p. 62).
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