Laboratory work
Dissociation constant of acetic acid
Purpose of the work: The purpose of this lab is to calculate the acid dissociation
constant (Ka) of acetic acid, HC2H3O2, and
verify that it is indeed a constant regardless of the concentration of the
acid.
Safety Precautions: Handle acetic acid with care -it will cause painful burns if it comes
into contact with skin or gets into eyes.
Materials:
·
CBL program
·
TI Graphing Calculator w/ Datamate program
·
Wash bottle filled with distilled water
·
100 mL graduated cylinder
·
pH Sensor
·
Pipette
·
Small beaker
·
2.00 M HC2H3O2
·
Stirring
rods
Procedure:
1.
Obtain and wear safety goggles.
2.
Plug the pH Sensor into Channel 1 of the CBL 2 interface. Use the
link cable to connect the TI Graphing Calculator to the interface. Firmly press
in the cable ends.
3.
Turn on the calculator and start the DATAMATE program. Press CLEAR to
reset the program.
4.
Select SETUP from the main screen.
5.
Press ENTER to select CH 1.
6.
Select PH from the SELECT SENSOR menu, and then select OK to return
to the main screen.
7.
Pour the calculated volume of acetic acid required for the lab into a
small beaker.
8.
Pour about 20mL of distilled water into a 100mL graduated cylinder,
followed by the calculated amount of acetic acid required to make a the assigned
molar solution in the same graduated cylinder. Then add more distilled water to
the graduated cylinder until the 100mL mark is reached.
9.
Stir the solution in the graduated cylinder thoroughly to prevent pH
readings from drifting.
10. Rinse the pH sensor with distilled water, and stick it into the
graduated cylinder to measure the pH of the solution.
11. Record the pH when the reading stabilizes.
12. Repeat Steps 8-11 with the 2nd assigned concentration of
acetic acid.
Questions:
1.
What is the electrolyte dissociation degree? What factors are
involved? How can it be increased, how can it be reduced?
2.
What is the electrolyte dissociation constant? What factors are
involved? In what case the dissociation constant increases, in what case
decreases?
3.
Write the equilibrium dissociation equation of Сu(ОН)2 and
Н3РО4. Write the formulas for the dissociation constant
for each step.
4.
Calculate the degree of dissociation of the acetic acid in 0.5 N
HCOOH solution. KHCOOH = 1.8 * 10-4.
5.
Calculate the degree of dissociation of acidic acid in the presence
of 0.1 N HCl solution in 0.5 N HCOOH solution. KHCOOH = 1.8 *
10-4.
6.
Write the molecular and ionic equations of the reactions of these
poorly soluble substances (ВаСrО4, Аg3РО4,
СаСО3, Сu(ОН)2, Fе(ОН)3).