1-35 Acid Base Titration

Name: ______Date: ______Period: ______

TITRATION OF AN ACID WITH A STRONG BASE

Introduction:

Nearly all of the adult population suffers from acid indigestion at some time. Although hydrochloric acid is present in the stomach, an excess can cause heartburn and a feeling of nausea. A common way to relive the pain of acid indigestion is to take antacids to neutralize the stomach acid. If you mix a solution of a strong acid containing hydronium (hydrogen) ions with a solution of strong base that has an equal number of hydroxide ions, a neutral solution results. In general, reactions in which an acid and a base react in an aqueous solution to produce a salt and water are called neutralization reactions. When the number of moles of hydrogen ions provided by the acid equal the moles of hydroxide ions provided by the base, the equivalence point has been reached.

If you wish to determine the concentration of an acid, you can neutralize the acid with a base of known concentration, known as the standard solution, using an indicator to show when the neutralization reaction is complete. This quantitative neutralization process is called titration. A titration is continued until the indicator shows that neutralization has just occurred. The point at which the indicator changes color is the end point of the titration. The point of neutralization is the end point of the titration. The titration process can also be used in a similar way to determine the concentration of a base if you use an acid of known concentration.

Objectives: When you have completed this activity, you should be able to:

1. Demonstrate the ability to determine the concentration of an acid using an appropriate indicator in the titration process.

2. Demonstrate the ability to measure liquid volumes with a buret.

3. Using experimental data, compute the molarity of an acid by either using the balanced equation and the principles of molar ratios or the rule: (NA) (Macid) (Vacid) = (NB) (Mbase) (Vbase)

4. Define end point, titration, and neutralization.

Materials:

goggles sheet of white paper

burets, 50 ml (2) the following chemicals:

double buret clamp deionized water

ring stand 0.100M NaOH standard solution

125 or 250 ml Erlenmeyer flask unknown concentrations of HCl

funnels (2) phenolphthalein solution in dropper bottle

waste beaker

Procedure:

1. _____ Read the starting volume of the acid buret accurately to 0.01 ml. Record it in the Data Table. Dispense approximately 10 ml of acid from the acid buret into a clean Erlenmeyer flask. In the data table, record the ending volume to the nearest 0.01 ml. Calculate the actual volume used and record in the data table.

2. _____ Add two drops of the phenolphthalein indicator to the flask and swirl to mix.

3. _____ Read the starting volume of base in the base buret to the nearest 0.01 ml and record.

4. _____ Put the flask under the buret containing the basic solution. Swirl the flask continuously while you slowly add base to the acid.

5. _____ As the endpoint of the acid is approached, the indicator color will remain for longer periods of time. As this occurs continue to add the base, one drop at a time. The endpoint is reached when one drop of base produces a faint trace of pink color that lasts for 10 seconds. (Use the white sheet of paper under the flask to help you detect the first faint trace of pink color.)

6. _____ When the endpoint is reached, read the ending volume in the base buret to the nearest 0.01 ml. Record this reading on the Data Table.

7. _____ Rise the flask and repeat the titration process with the second aliquot of acid.

Data Table

TRIAL #1

Acid buret – starting volume: ______ml / Base buret – starting volume: ______ml
Acid buret – ending volume: ______ml / Base buret – ending volume: ______ml
Volume of acid used in the
neutralization reaction: ______ml / Volume of base actually
neutralized: ______ml

TRIAL #2

Name(s): ______

Analysis:

1. Write a balanced equation for the neutralization reaction.

______

2. Compute the molar concentration of the acid solution using either the balanced equation and the principles of molar ratios, or the rule (NA) (Macid) (Vacid) = (NB) (Mbase) (Vbase). Compute each run separately. Then take the average of the two results unless they are drastically different. If this is the case, consult your teacher. Show all work in a logical, organized manner. Include units and report your answer in the correct number of significant figures.

a. Trial 1:

______

b. Trial 2:

______

c. Average Molarity:

______

3. Using the average molarity, unless otherwise told by the teacher, and the actual molarity of the acid solution, provided by the teacher, calculate the percent error for this experiment.

4. If each group working with the same unknown reported its results, the molar concentrations of acid would probably vary. Assuming that each group performed the titration accurately, suggest three reasons that could account for the varied results.

5. Suppose you performed this experiment using a sulfuric acid solution (H2SO4) at the same concentration as the acid solution you used earlier. Would the volume of 0.1 M NaOH needed to neutralize the sulfuric acid be the same or different as the volume of NaOH used here? How much different? Explain why or why not.

6. I did a titration where it took 25.0 mL of 5.00M NaOH to neutralize 1000. mL of an acid with an unknown concentration. Using this information, what was the concentration of the acid?

7. Do a little research. When are titrations used in the real world? Give 2 examples and briefly summarize the importance of it.

Pre-Lab

Part 1: Titration of an Acid With A Strong Base

1. Read the Introduction and the Procedure of the lab activity. Highlight the important information for the lab.

2. Why is the endpoint of a neutralization reaction important? How will you know when you have reached the endpoint?

3. Why is it important to perform the titration in duplicate?

Part 2: Practice Reading a Buret

1. What is the volume of the following burets? Remember… sig figs!!

a) ______b) ______

Part 3: Titration Dry-Run

2. You have an un-labeled bottle of HCl. You pour 25mL of the acid in a volumetric flask. To determine its concentration you perform a ______.

3. You first read the initial volume of the base 0.15 M NaOH in the buret to be ______mL.

4. You release the base until the endpoint is reached. The color that appears when the end point is reached is ______.

5. Then you read the final volume of the base used which is ______mL.

6. You calculate the total volume of base used to be ______mL.

7. You then calculate the concentration of the HCl to be ______M.