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7-3: Analysis of a Ferrous Chloride Sample Titrations provide a method of quantitatively measuring the concentration of an unknown solution. This is done by delivering a titrant of known concentration into an analyte of known volume. (The concentration of an unknown titrant can also be determined by titration with an analyte of known concentration and volume.) In oxidation-reduction (redox) titrations, the voltage resulting from the mixture of an oxidant and reductant can be measured as the titration proceeds. The equivalence point of the titration, or the point where the analyte has been completely consumed by the titrant, is identified the point where the voltage changes rapidly over a small volume of titrant delivered. In this assignment, you will determine the mass % of an unknown sample of ferrous chloride (FeCl) by titrating it with a KMnO solution of known concentration. 1. Start Virtual ChemLab, select Electrochemistry, and then select Analysis of a Ferrous Chloride Sample from the list of assignments. The lab will open in the Titrations laboratory. 2. You will have to drag the FeCl, bottle to the front of the lab bench to see the unknown number. Record the FeCl, Unknown number in the data table on the following page. Click the Lab Book to open it. Click the Beakers drawer and place a beaker in the spotlight next to the balance. Click on the Balance area to zoom in, open the bottle of unknown FeCl2 by clicking on the lid (Remove Lid). Drag the beaker to the balance to place it on the balance pan and tare the balance. Pick up the Scoop and scoop out some sample by first dragging the scoop to the mouth of the bottle and then pulling the scoop down the face of the bottle. As the scoop is dragged down the face of the bottle it will pick up different quantities of solid. Select the largest sample size and drag the scoop to the beaker on the balance until it snaps in place and then let go. Repeat this again so you have approximately 2 g of unknown in the beaker. Record the unknown number and the mass of the sample in the data table. Return to the laboratory. notred odio dilo ് 10 മി Ostoslom od 3. Place the beaker on the stir plate. Drag the 50 mL graduated cylinder under the tap in the sink and fill it with distilled water. It will automatically snap back into place when it is full. Drag the full 50 mL graduated cylinder to the beaker on the stir plate and then pour the water into the beaker. Now place the voltmeter probe in the beaker and make sure the voltmeter is on. bussion 4. The buret will be filled with 0.0815 M KMnO4. Click the Save button in the Buret Zoom View window so the titration data can be saved. The horizontal position of the orange handle is off for the stopcock. Open the stopcock by pulling down on the orange handle. The vertical position delivers solution the fastest with three intermediate rates in between. Turn the stopcock to one of the fastest positions. Observe the titration curve. When the blue line begins to tum up, double-click the stopcock to turn it off. Move the stopcock down one position to add volume drop by drop. There are two methods for determining the volume at the equivalence point: (1) Stop the titration when a color change occurs. Click the Stop button in the Buret Zoom View. A blue data link will appear in the lab book. Click the data link icon to open the Data Viewer window. Scroll down to the last data entry and record the volume at the equivalence point in the data table. OR (2) Add drops slowly through the equivalence point until the voltage reaches a maximum and levels off. Click the Stop button in the Buret Zoom View. A data link icon will appear in the lab book. Click the data link icon to open the Data Viewer window. Click the Copy Data button to copy and paste the data into a spreadsheet program. Plot the first derivative of voltage vs. volume. The peak will indicate the volume at the equivalence point since this is where the voltage is changing the most rapidly as the volume changes.