Pre Lab Experiment 6: Extraction, Recrystallization, Identification of Unknown Neutral and Acid

Question 1

What kind of compounds are in the unknown mixture?

Answer 1

A neutral and Acidic compound

Question 2

What extraction solvents are used?

Answer 2

Diethyl ether to dissolve the mixture. Then aq NaOH is added to dissolve the acidic compound by making it charged (like dissolve like). When the aqueous layer is extracted (containing the acid), you add aq HCl to neutralize the acid and add ether as the final extraction solvent. The organic layer now has the acid you want.

Question 3

What are Schlieren lines? What does the occurrence of this mean (solubility wise)?

Answer 3

Streaks or wavy lines in a solution indicating regions of different density (usually indicates that something is dissolving.
Translucent wavy lines can appear in solution along with undissolved solid
If Schlieren lines have been detected than some of the solid remains which means the mixture is partially soluble

Question 4

What were the solvents used for the solubility test of mixture for liquid-liquid extraction? Why were they used?

Answer 4

1) Diethyl ether
2) Water
3) 10% aq HCl
4) 10% aq NaOH
5) 5% NaHCO3
Mainly used to identify our unknown

Question 5

What were the 3 solvents to choose from for recrystallization?

Answer 5

Petroleum Ether, Ethanol, Water

Question 6

How do we make a solvent pair? What is the procedure for recrystallization with a solvent pair?

Answer 6

First, the two solvents must be miscible. One solvent needs to dissolve the compound at all temperatures. The other solvent should not dissolve the compound at all.
How to properly use solvent pair:
1) Add first solvent (5-10mL) that dissolves compound completely and heat.
2) Add second solvent (5mL) to solution until it becomes cloudy.
3) Add drops of first solvent just until cloudiness goes away.

Question 7

How do we know the true colour of crystals?

Answer 7

The true colour is known after grinding