chem lab

Michele Hopkins

General Chemistry II/ CHEM-182-DL1

Professor Amal Bassa

June 27, 2014

Introduction

This lab experiment is to help improve understanding with the theories in addition to techniques of

titration as well as to establish the strength of an acetic acid solution.

Procedure

1. I placed a thick text book on top of the LabPaq box to use as a titrator holder.

2. I than used the test tube holder to clamp the titrator which is simply a 10-mL syringe with an affixed

stop cock.

3. Next I placed a 100 mL beaker next to the box/book stack where it will sit under the titrator.

4. I than placed a small piece of white paper under the beaker to help in the observation of color changes.

5. I slipped the clamp handle into the textbook at a level where the stop cock tip is approximately

cm above the top of the beaker

6. I filled the syringe directly from the NaOH dropper bottle with 9 -10 ml of 0.5 M NaOH solution.

7. I than allowed a few drops of the NaOH solution to drip into the beaker.

Performing the Titration of the Vinegar Sample of Unknown Concentration

1. I used a graduated cylinder to measure exactly 5 mL of the vinegar sample and poured it into the

beaker.

2. I than added 2 drops of phenolphthalein solution to the vinegar sample in the beaker.

3. I placed the beaker with the vinegar sample and phenolphthalein drops under the titrator. Open

the stop cock to add only one drop of NaOH at a time to the water sample in the beaker.

4. Next I gently swirled the sample in the beaker after each drop and observe the color for five seconds.

Continued adding only one drop of NaOH solution at a time until the colorless vinegar changed

to pink and it remained that color for at least 30 seconds.

5. I than saved the titrator with its remaining NaOH solution for further use.

6. Next I repeated the above titration process two more times.

Titration for Acetic Acid in Vinegar

Peter Jeschofnig, Ph.D. Version 42-0208-00-01

Lab Report Assistant

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Observations

Data Table 1: Quantity of NaOH needed to Neutralize 5 mL of Acetic Acid Brand of Vinegar Used: Label Notes:
	Initial NaOH reading (Interpolate to 0.1 mL)	Final NaOH reading (Interpolate to 0.1 mL)	Volume of NaOH used
Trial 1	9.1 mL	0.3 mL	8.8 mL
Trial 2	9.0 mL	0.9 mL	8.1 mL
Trial 3	9.1 mL	0.8 mL	8.3 mL
Average volume of NaOH used:

Experiment

Titration for Acetic Acid in Vinegar

122

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Calculations

A. Calculate the average number of mL of NaOH used for the 3 trials and record.

B. Calculate the Normality of the vinegar using the previously given equation.

Na = (Nb)(Volumeb)

(Volumea)

C. Calculate the mass of the acetic acid in grams using the previously given equation.

Massa = (Na)(GMWa)

D. Calculate the percentage of acetic acid using the previously given equation.

% Acid = Massa(g/L) x 100

1000g/L

Questions

A. What is the average % acetic acid in your vinegar sample? Standard vinegar is 5% acetic acid. How does your result compare with the standard?

B. Why is it better to use white vinegar rather than dark vinegar for this titration? C. Write a balanced equation for the neutralization of acetic acid with NaOH.

D. How would your results have differed if the tip of the burette was not filled with sodium hydroxide before the initial volume reading was recorded?

E. How would your results have differed if you had over-titrated, i.e. added NaOH beyond the endpoint?

F. What happens if you don’t wear goggles and get some NaOH in your eyes?

G. A 5.0 mL sample of vinegar was titrated with 7.2 mL of 0.55 M NaOH(aq). If the density of the vinegar solution is 1.00 g/mL, what is the mass percent of acetic acid present?

Conclusion

During this experiment I exposed just how to carefully and precisely perform a titration, in order to reach a balance amongst in excess of Titrating as well as under titrating, and generate findings of a percentage make-up of an unknown solution by identifying the molarity/ strength of a pre-determined second solution.

Reference

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