Question

Please help with formulating a procedure to conduct this experiment

Objective: Student will be given approximately 1.00 g of an unknown solid mixture. The mixture will be primarily an unknown organic acid contaminated with a significant amount of an organic neutral compound. Student is required to separate and purify the organic acid. The melting point will be taken, and the samples will be returned to the instructor in a labelled vial.

Students must have a complete procedure written out in their notebook when they show up for lab. The instructor will check notebooks as the students enter the lab. Anybody without a satisfactory procedure will not be permitted to enter the lab. For the purposes of planning the procedure, students may assume that there are 9 mmol of acid in their sample.

To limit waste, each student will be given 20 mL of dichloromethane to use during the lab.

Materials: The following materials will be available for the students to use:

            Student drawer contents

Small filter flasks (to be signed out from instructor)

            20 mL Dichloromethane (provided by the instructor)

            Saturated NaHCO₃

            1.5 M NaOH

            6 M HCl

            DI Water

            Anhydrous MgSO₄

            95 % Ethanol

            Hot plates

Answer 1

1. Initially the mixture of compounds has to dissolve in given 10 mL chloroform.

2. Now dilute the organic solution with minimum amount (10 ml) of water.

3. Adjust PH to basic by using 1.5 M solution of NaOH slowly by adding dropwise at 0 - 10 ^oC.

4. All acid the convert as acid salt and dissolve in water. The organic layer contains only neutral compound which can be separated. We evoparate the organic solvent (chloroform) to get pure neutral compound and recollection of organic solvent has done here (chloroform)

5. Now the aqueous layer which is basic in nature contains the acid compound as salt.

6. Now adjust PH to 1-2 slowly by adding 6 M HCl solution at 0 - 10 ^oC, while doing the process acid slowly getting precipitated out.

7. Cool the layer to 0 ^o C to get all the acid compound get precipitated out.

8. Now filter the acid compound to get pure compound.

9. If the acid doesn't get precipitated then extract with chloroform (10mL) and the organic layer dry over anhydrous Mg SO4 and evoparate completely to get acid compound.

Purification : the above obtained acid compound dissolve in 95% hot ethanol and settle down to get crystalline compound. Now measure the melting point to confirm and measure the purity of the compound.

Use of NaHCO3 : while adjusting PH NaOH is strong Base compared to NaHCO3, so that at last stage of PH adjustment we use NaHCO3.

Hot plate: we use hot plate in purification process (ethanol crystallisation process) to dissolve completely in minimum ethanol.