Pi Day Tech Tips: Tip 4

Blog Date: 
Friday, March 14, 2014

Acid-Base Titration

adapted from Experiment 24,"Acid Base Titration" from the Chemistry with Vernier lab manual

Objectives

In this experiment you will:

  • Use the Drop Counter to monitor the volume NaOH added to the HCl solution.
  • Use a pH Sensor to monitor changes in pH as sodium hydroxide solution is added to a hydrochloric acid solution.
  • Use the results to calculate the concentration of the hydrochloric acid solution.

Materials
 

  • LabQuest
  • Vernier Drop Counter
  • 60mL Reagent Reservoir
  • Vernier pH Sensor
  • 0.1 M NaOH Solution
  • Unknown Concentration HCl Solution
  • 250mL Beaker
  • Phenolphthalein
  • 10mL Graduated Cylinder
  • 100mL Graduated Cylinder
  • Ring Stand
  • Clamp
  • Stir plate
  • Magnetic Stir Bar or Microstirrer
  • Wash Bottle
  • DI water

 
Procedure

1.   Obtain and wear goggles.
2.   Add 40 mL of distilled water to a 100 mL beaker. Add 5.00 mL of the HCl solution into the 100 mL beaker with distilled water.
3.   Obtain approximately 40 mL of 0.1 M NaOH solution in a 250 mL beaker. Record the precise NaOH concentration in your data table.
4.   Attach the drop counter to the ring stand approximately half way up.
5.   Obtain the plastic 60 mL reagent reservoir. Close both valves by turning the handles to a horizontal position.
Use a utility clamp to attach the reagent reservoir to the ring stand. Add the NaOH solution to the reagent reservoir.
Drain a small amount of NaOH solution into the 250 mL beaker to fills the reservoir’s tip. To do this, turn both valve handles to the vertical position for a moment, then turn them both back to horizontal.
6.    Connect the pH Sensor to CH 1 of LabQuest. Connect the Drop Counter to DIG 1 on the top of the right side of the LabQuest. Power on the LabQuest using the power button on the top left of the device.
7.   Assemble the apparatus.
Place the magnetic stirrer on the base of the ring stand.
Insert the pH Sensor through the large hole in the Drop Counter.
Attach the Microstirrer to the bottom of the pH Sensor. Rotate the paddle wheel of the Microstirrer and make sure that it does not touch the bulb of the pH Sensor.
Adjust the positions of the Drop Counter and reagent reservoir so they are both lined up with the center of the magnetic stirrer.
Lift the pH Sensor, and slide the beaker containing the HCl solution onto the magnetic stirrer. Lower the pH Sensor into the beaker.
Adjust the position of the Drop Counter so that the Microstirrer on the pH Sensor is just touching the bottom of the beaker.
Adjust the reagent reservoir so its tip is just above the Drop Counter slot.
8.   Turn on the magnetic stirrer so that the Microstirrer is stirring at a fast rate.
9.   To start data collection, press the collect button in the middle of the device above the center navigation buttons. No data will be collected until the first drop goes through the Drop Counter slot. Fully open the bottom valve—the top valve should still be adjusted so drops are released at a rate of about 1 drop every 2 seconds.
10.   During the titration, determine when a large increase in pH takes place—this will be the equivalence point of the reaction. When this jump in pH occurs, let the titration proceed for several more milliliters of titrant, then stop data collection and close the bottom valve on the reservoir.
11.   To examine the data, go to the table of pH vs. volume to find the equivalence point. Scroll down to the points where the largest increase in pH was. Find the NaOH volume just before this jump. Record this value in the data table. Then record the NaOH volume after the drop producing the largest pH increase was added.
12.   If time permits, repeat the titration, refilling the NaOH reservoir as needed.

 

Data

Data Table 1

 

Data table for experiment results
  Trial 1 Trial 2 Trial 3
Concentration NaOH M M M
NaOH volume added before largest pH increase mL mL mL
NaOH volume added after largest pH increase mL mL mL
Volume of NaOH added at equivalence point mL mL mL
Moles NaOH mol mol mol
Moles HCI mol mol mol
Concentration of HCI mol/L mol/L mol/L
Average Concentration of HCI     M

Questions

1.    What is the balanced equation for the experiment?
2.    Does you experimental mole ratio match the theoretical values? If not, what are possible sources of error?
3.    Are your values for concentration of HCl repeatable? What is your average value for the concentration of HCl?