Standardizing a Solution of Sodium Hydroxide PURPOSE:
To determine the concentration of sodium hydroxide.
OBJECTIVES:
● ∙ Prepare an aqueous solution of sodium hydroxide to a target molar concentration.
● ∙ Determine the concentration of your NaOH solution by titrating it with a solution of potassium hydrogen phthalate, abbreviated KHP, of precise molar concentration.
MATERIALS:
LabPro or CBL 2 interface
solid sodium hydroxide
computer or handheld
solid potassium hydrogen phthalate, KHP
Vernier pH Sensor
distilled water
ring stand
plastic weighing dish or weighing paper
250 mL beaker
balance
250 mL Erlenmeyer flask
utility clamp
50 mL and 100 mL graduated cylinders
buret and buret clamp
magnetic stirrer and stirring bar
100 mL graduated cylinder
PROCEDURE
1. Measure out 100.00 mL of distilled water into a 250 mL Erlenmeyer flask. 2. Set up the data collection system. Connect a LabPro or CBL 2 interface to the computer or handheld with the proper cable.
a.
Connect the pH Sensor to Channel 1 of the interface.
b.
Start the data collection program.
c.
Set up data collection for Events with Entry mode.
3. Measure out the mass of NaOH that is needed to prepare a 0.10 M solution and add it to the flask of distilled water. Swirl the flask to dissolve the solid. CAUTION: Sodium hydroxide solution is caustic. Avoid spilling it on your skin or clothing. 4. Measure out the mass of KHP that will neutralize 25 mL of 0.10 M NaOH solution.
Dissolve the KHP in about 50 mL of distilled water in a 250 mL beaker. 5. Set up a ring stand, buret clamp, and buret to conduct a titration (see Figure 1). Place a utility clamp on the ring stand to hold the pH Sensor in place during the titration. 6. Rinse and fill the buret with the NaOH solution. Place a magnetic stirring bar in the beaker and place the beaker of KHP solution on a magnetic stirrer under the buret. Connect the pH Sensor to the utility clamp so that the tip of the sensor in immersed in the KHP solution but does not interfere with the movement of the magnetic stirring bar. 7. Conduct the titration carefully. When you have completed the titration, dispose of the reaction mixture as directed. Before conducting a second titration you may wish to print a copy of the results of your first titration, save the data, or record your data in a table or chart. 8. Use your titration data to find the equivalence point, which is the largest increase in pH upon the addition of a very small amount of NaOH solution. A good method of determining the precise equivalence point of the titration is to take the second derivative of the pHvolume data, a plot of D2pH/Dvol2. 9. Repeat the titration with a second
