Week 7: Coordination Chemistry 3 Overview Getting Started Techniques Procedure FAQ Full Lab Manual Introduction & Goals Chemistry & Background Key Questions Prelab Problems Safety Procedure In Your Write-up Experiments Index ChemLab Home		Before Lab Before coming to lab, prepare your prelab, including the objective, reference, prelab problems, procedure, and analysis flowchart or sample calculations. During Lab Record any deviations from the prelab procedure in your notebook. Be sure to record your partner's name and reference your partner's notebook, if data is copied from it. It is not necessary to copy the titration data for your partner's samples. Plot the titration curves for your samples in your notebook as you measure them . After Lab The postlab write-up of this laboratory is substantial because a simple potentiometric titration curve, although easily obtained, contains a great deal of information. The Results section of your write-up should include the following points: • Start by plotting the experimental titration curve and locating the end point, the point at which the plot of pH vs. V2 rises most steeply. Calculate the number of millimoles of [Co(NH3)5(H2O)][NO3]3 in the sample from the end point position. Use this and the mass of sample to calculate an experimental value of the molar mass of your complex. Compare this experimental molar mass to the theoretical value predicted from the chemical formula. This comparison is an indication of the purity of your compound. • Record the experimental molar mass values for all members of your lab group and average them. Use a statistical uncertainty analysis to calculate a 95% confidence interval as an uncertainty in the average molar mass. • Calculate an experimental acid dissociation constant Ka from the pH at the half-equivalence point and compare it with the literature value. Recall that the literature value is for an infinitely dilute solution and that ions present in your solution will cause your experimental Ka value to be smaller than the literature value. Such a difference is not an error. The Discussion for the Acidity of the Water Ligand experiment should address the following points. • Summarize your results for the experimental molar mass, the uncertainty in the average molar mass for your lab group, and the experimental Ka value. • Discuss the accuracy and precision of your results. Compare the statistical uncertainty of your lab group's average molar mass to the uncertainty implied by significant figures. How could the uncertainty be reduced, for your individual determination and for the entire lab group?
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