Analysis of Drain Cleaners

(Vernier Version)

For this version of the lab, you will follow the directions below for setting up the same titration lab as in the original.

  1. Use ~ 5 mL of the 0.10 M HCl solution to rinse the buret. Clamp the buret to a ring stand.
  2. Fill the buret past the 0-mL mark with HCl solution.
  3. Drain some of the HCl through the tip into a waste beaker to fill the tip and bring the level of HCl to exactly 0.00 mL. If the 0.00 mL mark is passed, use a dropper to bring the meniscus to 0.00mL. Make sure the buret tip is filled with acid.
  4. Place a clean 250-mL beaker on the balance and tare. Record the value.
  5. Using the pipet, add 3.0 mL of drain cleaner to the beaker. Record the mass of the drain cleaner.
  6. Add ~ 75 mL of distilled water to the beaker.
  7. Place the magnetic stirrer in the beaker, and turn on the stirrer slowly. Immerse the electrode in solution, keeping the electrode above and to the side of the stirring bar, being careful not to hit the pH electrode.
  8. Prepare the computer for data collection by opening the file in the Experiment 24 folder of Chemistry with Computers. The vertical axis has pH scaled from 0 to 14 pH units. The horizontal axis has volume scaled from 0 to 25 mL. Change the values on the horizontal axis to 0 to 50 ml by double clicking on the x-axis and entering 50 in the dialog box.
  9. Before adding HCl titrant, click [Collect] and monitor pH for 5-10 seconds. Once the displayed pH reading has stabilized, click [Keep]. In the edit box, type “0” (for 0 ml added). Press the ENTER key to store the first data pair for the experiment.
  10. You are now ready to begin the titration.
  11. Add the next increment of HCl titrant (enough to raise the pH about 0.2 units). When the pH stabilizes, again click [Keep]. In the edit box, type in the current buret reading, to the nearest 0.01 ml. Press ENTER. You have now saved the second data pair for the experiment.**
  12. Continue adding HCl solution in increments that raise the pH by ~ 0.2 units and enter the buret reading after each increment.
  13. When you notice the curve in the graph beginning to quickly increase, start adding the titrant in one-drop increments. Save these data points.
  14. When the curve begins to level off, you may add larger increments of titrant again.
  15. Continue to add acid until a pH of less than 3.0 is obtained then you may stop the experiment.
  16. To determine the end-point of the titration, you can take advantage of the Vernier software program.
  17. First, add a connecting line to your data points by clicking on View – Graph Options – and check the “connecting line”.
  18. The region of most rapid pH change is used to determine the equivalence point. This point is in the middle of the vertical part of the curve. To determine the volume of HCl titrant at this point, click the “examine” button on the tool bar and pass the cursor over the graph. A dialog box will appear indicating what the data points are for that particular location. Record the volume of HCl.
  19. There will probably be two inflection points on the graph. The midpoints of these regions represent two different endpoints, the first for NaOH, and the second for NaOCl. Using the volume of acid to reach each endpoint, the concentration of the hydrochloric acid, and the formula weights of the components (NaOH and sodium NaOCl), calculate the percentage of each by weight.