 We're going to perform an experiment to determine the KSP for the slightly soluble compound silver chromate. In order to determine the KSP of the compound, we need to be able to determine the equilibrium concentration of one of the ions. We're going to use the chromate ion because it has a yellow color in solution. We're going to prepare a series of standard solutions of known concentration of potassium chromate. We're going to measure the absorbance of those solutions using a Spectronic 20. We'll then prepare a set of samples of silver chromate. We'll need to wash the samples, remove the excess reactant, we'll then add some potassium nitrate and let the solutions come to equilibrium. The potassium nitrate is used to maintain the ionic strength in the solution. Consistence systems have come to equilibrium, we'll measure the chromate ion concentration in the solutions, we'll use the chromate ion concentration to determine the silver ion concentration and then the KSP. We've prepared a series of standard solutions of potassium chromate. We're going to measure the absorbance of these solutions and create a Beers law plot of absorbance versus the molarity of the potassium chromate solutions. This will allow us to determine the chromate ion concentration from our silver chromate. We've set the wavelength on our Spectronic 20 to 375 nanometers, which is where the potassium chromate absorbs. We're going to set the 0 percent T with no sample in the sample container. We're going to set the 100 percent T by taking a cuvette filled with .25 molar potassium nitrate. We're going to set the 100 percent T with .25 molar potassium nitrate. We'll remove the cuvette containing the potassium nitrate solution, we'll empty the cuvette and rinse it with one of our standard solutions. We'll place the cuvette into the sample holder and we'll read the percent T from this dial and calculate the value for A. We're going to prepare our sample of silver chromate by mixing a solution of silver nitrate and potassium chromate. We undergo a double displacement reaction to produce silver chromate. You can manually mix this so that it's thoroughly mixed and the compounds have a chance to react. If you happen to have a vortex mixer, you can mix this very rapidly. You want to mix this for a couple of minutes in order for the reaction to reach equilibrium. We need to remove the excess reactant. In order to do that, we're going to centrifuge our sample. We're going to place our sample in one side of the centrifuge. We're going to place a test tube filled with water opposite it to balance it in the centrifuge. We're going to spin this for a couple of minutes. We're going to remove the sample from the centrifuge. Most of solid is then thrown to the side and bottom of the centrifuge tube. We're going to carefully decant the solution, which will contain the excess potassium chromate. We'll add a small amount of potassium nitrate to the test tube, cover with parafilm again, and we'll mix it for a few minutes. What we're trying to do is wash out any unreacted starting material. After a couple of minutes of shaking, we will then re-centrifuge the sample. The solid has been spun to the bottom of the test tube. We'll carefully decant the liquid. We'll do a separate rinsing, adding some more potassium nitrate. We'll cover it with parafilm. We'll shake it for another five minutes, and then we'll re-centrifuge the sample. The solids again at the bottom of the test tube will carefully decant the liquid. We've now rinsed the solid enough to have removed unreacted starting material. We're going to add another five milliliters of potassium nitrate solution. We're going to cover it again with parafilm. We're going to shake this for about ten minutes. That should establish an equilibrium between the solid and the ions in solution. After ten minutes shaking, we'll spin down the sample. We're going to remove our sample from the centrifuge, and we're going to carefully pour the solution into our cuvette. We'll try carefully not to get any solid in the cuvette. We'll wipe down the sides of the cuvette, and we'll place the cuvette in our spectrophotometer, and we'll read the percent T from the meter and calculate the A value. We'll read the percent T value from the meter and calculate the absorbance. We'll use the Beer's Law plot of absorbance versus concentration from our standards to determine the concentration of the chromate ion in solution. We use the chromate ion concentration to calculate the silver ion concentration, and with the silver ion concentration and chromate ion concentration, we'll calculate the KSP value for silver chromate.