Beyond Labz 6-9: Acid-Base Titration: Unknown HCl Titrations provide a method of quantitatively measuring the concentration of an unknown solution. In an acid-base titration, this is done by delivering a titrant of known concentration into an analyte of known volume. In this assignment, you will titrate a 0.2564 M solution of NaOH into 25 mL of an unknown concentration of HCl and calculate the concentration of the HCl solution.1. Start Virtual ChemLab, select Acid-Base Chemistry, and then select Acid-Base Titration: Unknown HCl from the list of assignments. The lab will open in the Titrations laboratory.2. Click the Lab Book to open it. Click the Buret Zoom View window to bring it to the front. The buret is filled with 0.2564 M NaOH. The beaker has 25.00 mL of unknown HCl. The pH meter is turned on and has been calibrated. The indicator is bromocresol green.3. Perform the titration. 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 in the graph window (the pH curve) begins to turn 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 (close the stopcock) when a color change occurs, and then 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 View window. Scroll down to the last data entry and record the volume at the equivalence point. OR (2) Add drops slowly through the equivalence point until the pH reaches approximately 12. 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 View window. Click Copy Data button to copy and paste the data to a spreadsheet program. Plot the first derivative of pH vs. volume. The peak will indicate the volume of the equivalence point since this is where the pH is changing the most rapidly as the volume changes.4. What is your unknown sample number?5. What volume of 0.2564 M NaOH was required by the titration to reach the equivalence point?6. Calculate the molarity of the HCl using 25.00 mL of HCl solution and the volume of the 0.2564 M NaOH from your titration.
