Coordination Chemistry 2 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		Gravimetric Analysis Record the mass of an empty, dry, uncapped, and unlabeled vial. Accurately weigh between 0.2 and 0.25 g of your cobalt salt into the vial and place it in a beaker. To identify your sample, put a slip of paper with your name on it inside. Place the beaker in the drying oven, set at 110°C for about 45 minutes. Remove the beaker from the oven, using tongs. After cooling the sample on the bench top for about 10 minutes, move the sample to a desicator jar, for further cooling, for about 30 minutes. When the vial reaches room temperature, weigh it on the analytical balance. Repeat the heating, cooling, weighing cycle until the mass is the same, to within 0.0003 g. Beer's Law Test Prepare a set of solutions with differing concentrations using the stock solution, a 25 mL volumetric flask, and various sized volumetric pipets. The following links will help you review the use of this glassware. Pipet Volumetric flask When solutions are properly diluted, make sure they are well mixed. You should have 5 different solutions, counting the stock solution, with varying concentrations, for your Beer's Law calibration plot. Measure the absorbance of each solution at 625 nm. Zero the Spec 20 before each reading, with a 50/50 acetone water blank. Analysis of Cobolt Complex Begin the analysis by making a solution of your cobalt complex. Accuately weigh about 20 mg of solid and dissolve it in water in a 25 mL volumetric flask. When the solid is completely dissolved, carefully dilute to the mark with water. Use the following links to review the use of the Volumetric flask and Analytical balance You will pipet a 2 mL sample of the complex solution into two different beaker, for duplicate analysis. Add 2.00 mL of 1 M NaOH to each beaker and heat the solutions for 15 minutes. Heat gently, below the boiling point. At the end of this period, all color should be gone from the solution and a fine brown precipitate should be seen on the bottom of both beakers (left). Add 2 mL of 6 M HCl to each beaker and continue heating for 10 more minutes. During this time, the solid should dissolve, giving nearly colorless solutions (right). Transfer the sample from one beaker to a 25 mL volumetric flask. Rinse thoroughly, making sure your transfer is quantitative. add 12.5 mL of PURE acetone and 2 mL of NH4SCN solution to the flask. Dilute to the mark with water and mix. Transfer the solution to a cuvet and measure its absorbance with a Spec 20, calibrating with an acetone/water blank. Repeat the process of making a solution and measuring its absorbance with the sample in the second beaker. You will compare the results of these duplicate analyses to evaluate your precision.
Trustees of Dartmouth College, Copyright 1997–2001