Organic Chem

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  • Topic: Acetic acid, Carboxylic acid, Acid
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Organic Lab I No. 5-6
Separation of a Carboxylic Acid, a Phenol, and a Neutral Substance (Two-week lab)

Reading Assignment

1) Chapter 7

• Introduction: P. 135- first paragraph

• Theory and Techniques (p142-145)
o Properties of Extraction Solvents
o Mixing and Separating the Layers
o Drying Agents
o Part 1: The Technique of Neutral Liquid/Liquid Extraction The description is for dichloromethane-aqueous solution mixture, but you will use the same technique for your tert-butyl methyl ether-aqueous solution mixture. Note, however, that the ether is less dense than water, while dichloromethane is denser than water. o Part 2: Acid/Base Liquid/Liquid Extraction (p.147-150 middle)

2) THIS HANDOUT: Scheme of Procedure and Reaction Equations


(1) Due the beginning of Lab No. 6: Answers to the post-lab questions (see below) (2) Due the beginning of Lab No. 7: Formal Report (see Guideline)

Post-lab questions

1. When you have a two-layer mixture of water and tert-butyl methyl ether, what physical property of these liquids assures you that ether is the top layer?

2. Explain how a phenol can be separated from a mixture of a phenol and a neutral compound using the acid-base extraction method.

3. In this separation experiment, you first extract a carboxylic acid with NaHCO3(aq), then extract a phenol with NaOH(aq). Can you reverse the order? Why or why not?

4. You perform each extraction twice, first with 1 mL and second with 0.15 mL. Why is the second extraction necessary?

5. What is the purpose of washing an ether solution with saturated NaCl solution?

6. What is the purpose of using CaCl2 pellets?

(More questions next page!)

a) If your carboxylic acid is benzoic acid, how many moles of benzoic acid are present in your sample? b) How many moles of sodium bicarbonate are contained in 1mL of a saturated solution of NaHCO3 (approximately 1g of solute is dissolved per 9mLsolution)? c) Is the amount of sodium carbonate sufficient to react with all of the benzoic acid? d) To isolate the carboxylic acid from the sodium bicarbonate solution, it is acidified with concentrated hydrochloric acid (the concentration is approximately 12M). What volume of acid is needed to neutralize 1mL of saturated bicarbonate solution?

Guidelines for Formal Report

• Type with Times or Times New Roman font, 12 point size. • Equations and calculations may be hand-written.

Your report must include:

• Your Name and Section
• Title, Objective, Dates of Experiment
• Equations for Reactions (2 for acid-base extraction, 2 for recovery) • Procedure

This part should be written in the past tense and in the third person.

You should describe what was actually done by you (do not just convert the textbook procedure into the third person). Divide the procedure into paragraphs with short subtitles.

For example:

Extraction of carboxylic acid
A mixture ( g) of a carboxylic acid, a phenol, and a neutral substance was weighed and placed in a reaction tube (tube 1). tert-Butyl methyl ether (=“ether”, xx mL) was added to the tube and the solid was dissolved. 1mL of sat. NaHCO3 solution was added to the tube and the content was mixed well by repeating drawing some liquid and forcing it out. After separation of two layers, the bottom layer was transferred to tube 2. …

• Results
Summarize the recovery yields and melting points of the three components. Calculate the % recovery (show calculation) assuming that the mass ratio of the three components was 1:1:1. As a theoretical yield of each component, use 1/3 of the mass of the mixture you started with.

• Conclusion
Based on the melting points,...
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