Prelab
Lab: Determining Ka of Acetic Acid
1. Read over the lab.
The following questions (2-6) are the theoretical answers to what you will
hopefully determine experimentally in this lab. They can be used to help
you formulate a hypothesis, and do the calculations at the end of the lab.
2.
3.
4.
5.
6.
Write the chemical equation for the neutralization of acetic acid with sodium
hydroxide.
Write out the expression for the hydrolysis of acetic acid.
Write out the expression to determine the Ka for acetic acid.
Find out (look up) the actual Ka of acetic acid.
25.0 mL of acetic acid is titrated with 0.20 M sodium hydroxide.
a) If 68.75 mL of NaOH was required to reach the endpoint, what is the
concentration of acetic acid?
b) Given the textbook value for Ka, what should the [H3O+] and pH be at the
beginning of the titration?
c) What would be the pH at the halfway point (half the volume of base added)?
d) Calculate the pKa (-log Ka). Compare this answer to c).
7. The purpose of this lab is to experimentally determine the Ka of
acetic acid.
a) State a hypothesis. Make sure it includes an “if…..then…..because”
statement.
b) Make a data table. By reading over the lab, you should know what
you need to record.
Questions 8- 12 involve a review of titration technique from grade 11.
8. In this lab, What chemical goes into the burette? What chemical goes into the flask?
9. What must you ensure, with respect to filling the burette, before beginning the
titration?
10. If you are right handed, where should your right hand be and where should your left
hand be when titrating?
11. What is a meniscus? Where do you read the meniscus?
12. What should you use when reading the meniscus?
13. To how many decimal points should you read your burette?
14. What range of pH does phenolphthalein indicator change colour in ?