Laboratory Techniques I, CHY 114
Chemistry Department, University of Southern Maine

Acid-Base Titration

Titration Apparatus

Assignment

In the index of your classroom text, look up and learn all you can about the following topics:

  • titration, acid-base
  • indicators, acid-base
  • monoprotic and diprotic acids

Read all you can find on these subjects. Study with particular care any sections that you have already covered, or will cover, in CHY 113. Before coming to lab, be sure that you understand terms in boldface in the Goal and Overview sections below.

Goal

To employ the method of titration in order to measure either

  1. the molarity of a monoprotic acid solution, or
  2. the molar mass of a solid monoprotic acid.

Overview

  • In Part 1, you will standardize (accurately determine the concentration of) a solution of a base, sodium hydroxide, using a weighed sample of a very pure solid acid, which is called a primary acid standard.
  • In Part 2, you will use your standardized base solution to titrate a solution of your unknown acid, using the indicator phenolphthalein to detect the end-point of the titration.
  • Using the known molarity of the sodium hydroxide solution and the end-point volume of base solution, you will compute either the molar mass of the solid acid (Procedure 2A), or the molarity of a solution of the unknown acid (Procedure 2B).

Preparing for Lab

The following problems require calculations similar to those called for in the report for this experiment. Learn how to work these problems, showing your calculations with units. Similar questions may appear on your prelaboratory quiz. For guidance, look at the Report Form for this experiment.

  1. Potassium hydrogen phthalate (KC8H5O4, but usually abbreviated KHP, 204.23 g/mol) is a monoprotic acid (provides one hydrogen ion per mole) that is used for standardizing bases. Calculate the mass of this acid that would react completely with 20.0 mL of 0.100 M NaOH.
    ANSWER: 0.408 g.
  2. A student titrates a solution containing 0.254 g of a monoprotic acid in 35 mL of water. The student reaches the endpoint after adding 18.35 mL of 0.107 M NaOH. How many moles of the acid are present in the sample?
    ANSWER: 0.00196 moles of acid.
  3. What is molecular weight of the acid?
    ANSWER: 129 g/mol.
  4. Titration of 10.00 mL of a solution of a diprotic acid requires 14.35 mL of 0.107 M NaOH to reach the endpoint. What is the molarity of the acid solution?
    ANSWER: 0.0765 M.

Procedures

Download and print the Procedure for this experiment. Study it carefully after reading this page. It's a good idea to translate the procedure into step-by-step instructions for your lab work. Bring the printed procedure and your instructions with you to lab. Once per semester, you might earn a free perfect quiz score for bringing good translated instructions.

Report

Download and print the Report Form for this experiment. Bring it with you to lab.

If it is not convenient for you to visit this page online, you might want to print it out as well.

CHY114 Lab Manual