Uploaded by Ahmad Zaidi Bin Zakaria


(BSCH 1212)
Extraction is the first step to separate the desired natural products from the raw materials.
Extraction works according to the principle that soluble components can be separates from
insoluble or less soluble components by dissolving them in a suitable solvent such as water,
hexane, alcohol etc. Raw materials that are suitable for extraction may contain either solids
only, solids and a solution, or solids and a liquid. Commonly the extract is the product or
intermediate product, and the residue is a waste.
To isolate neutral compound from a mixture containing an acid impurity.
To determine the name of an unknown compound from its melting point.
Diethyl ether, NaOH, HCl, benzoic acid, unknown neutral compound, saturated NaCl solution,
anhydrous NaSO4
Weighing scale, weighing boat, measuring cylinder, dropper, separating funnel, beaker, round
bottom flask, centrifuge tube, conical flask, capillary tube, melting-point apparatus, filter paper,
litmus paper, rotatory evaporator
1. Weigh the unknown neutral compound and benzoic acid
2. Put both compounds in a centrifuge tube
3. Measure 10 ml of diethyl ether
4. Pour the diethyl ether into the centrifuge tube
5. Shake well until all solids dissolve
6. Ensure the solid has completely dissolved
7. Pour the solution into a separating funnel
8. Measure 5 ml of NaOH solution
9. Pour the NaOH solution into the separating funnel
10. Take out the separating funnel from the ring
11. Shake the solution well
12. Open the separating funnel’s tap to release pressure
13. Repeat the “shake” and “pressure-release” steps at least thrice
14. Put back the separating funnel into its ring
15. Open the cap and wait until two layers of solutions appear
16. Drain the aqueous layer into the “1st NaOH flask”
17. Control the tap opening to ensure only aqueous layer is drain out
18. Add another 5ml of NaOH solution
19. Repeat the “shake” and “pressure-release” steps at least thrice
20. Drain the aqueous layer into “2nd NaOH flask”
21. Add more HCl until white precipitate form
22. Check the acidity solution for both NaOH flask using blue litmus paper
23. Measure 5ml of saturated NaCl solution
24. Add the NaCl solution into the remaining organic layer
25. Repeat the “shake” and “pressure-release” steps at least thrice
26. Remove the aqueous layer
27. Control the tap opening so it flows out slowly
28. Collect the organic layer into a clean dry flask
29. Add more anhydrous NaSO4 into the organic layer until no clumping form
30. Pre-weigh round bottom flask
31. Filter the NaSO4 from the organic layer into the round bottom flask
32. Put the round bottom flask into rotary evaporator to evaporate the ether
33. Weigh the round bottom flask with the unknown compound
34. Measure the melting point of the unknown compound to predict the compound
Data and observation:
MASS (g)
Neutral compound
Benzoic acid
There are two layers of solution in appear in the separating funnel
MASS (g)
Round bottom flask
Round bottom flask + unknown compound
Unknown compound
Solution in 1st NaOH flask
White precipitate appears
Solution in 2nd NaOH flask
Less white precipitate appears
Solution in 1st NaOH flask
Blue litmus paper turns red
Solution in 2nd NaOH flask
Blue Litmus paper turns red
Melting Point of an unknown compound = 114.45 °C
When adding NaOH solution into the separating funnel and shake the mixture there will be two
layers form. This is because NaOH will neutralize benzoic acid to form benzoate salt which is an
ionic compound and located in aqueous layer due to its solubility in ionic solution while the
neutral compound which is the organic compound will remain in organic layer with diethyl ether.
Aqueous layer located below organic layer due to its higher density compare to organic solution.
Adding HCl solution into each NaOH flask cause sodium benzoate salt to react with HCl that
produce solid benzoic acid which is the white precipitate and NaCl that dissolve in the aqueous
layer. 1st NaOH flask shows major white precipitate form compare to 2nd NaOH flask because
most benzoic acid has been removed in 1st NaOH flask. The blue litmus paper turns red because
the solution is acidic.
Saturated NaCl solution is added into the organic layer to remove excess water since NaCl is
ionic compound it dissolves in water so it can be removed. Anhydrous NaSO4 is added into the
organic layer until there is no clumping to ensure water is removed completely.
The melting point measured is 114.5 °C so from the given compounds we can conclude that the
unknown compound is Fluorene which has only 1.5°C difference from 116°C, so the compound
is pure.
Percentage recovery of the unknown compound: (0.1868 / 0.2572) x 100% = 72.68%
1. Consider the following solvent pairs. If mixed together, which pairs would form two layers? If
they form two layers, which solvent would be on top?
Compound pairs
Hexane and water
Two layers
Position of solvent
Hexane on top
Water and methylene chloride
Water on top
Hexane and methylene chloride
Not appear
Methanol and hexane
Hexanes on top
Ethanol and water
Not appear
Acetone and toluene
Not appear
2. You have 100 mL of water and add 4 mL of ether to it. You notice only one layer. Then, you
add 6 mL of ether more and see a small layer of a clear liquid on top of the water. Explain what
is happening.
Diethyl ether is soluble in water to a small extent
3. You want to extract a compound from water and have determined that the compound is
equally soluble in both hexane and diethyl ether. Which solvent would be the better choice for
the extraction?
Hexane because it is more soluble in water and less flammable
4. The distribution coefficients for a compound are as follows:
Kcyclohexane/water = 1.5
Kpentane/water = 11.2
Kdiethyl ether/water = 5.1
You have an aqueous mixture of the compound. Which solvent system, cyclohexane/water,
pentane/water, or diethyl ether/water, would give the most efficient extraction into the organic
Pentane/water because of highest distribution coefficient so it will be the suitable choice for
extraction into the organic solvent.
5. Five grams of Compound A is dissolved in 90 mL of water. The distribution coefficient for
Compound A between hexanes and water is 5 (in other words, KCompound A(hexanes/water) =
a) How much of Compound A will be in the hexane if you extract it from the water one time
with 90 mL of hexanes?
K = 5 = x g in 90ml hexane/ (5-x) g in 90 ml water
5 = x / 5-x (90 ml cancels)
x = 4.2 g
b) How much of Compound A will be in the hexane if you extract it from the water with
three sequential extractions using 30 mL of hexanes each time, and then combine the
hexanes extracts?
K = 5 = x g in 30 ml hexane / (5-x) g in 90 ml water
5= 3x/ (5-x)
x = 3.1 g
5 - 3.1 g = 1.9 g of the compound in the water, therefore:
K = 5 = x g in 30 mL hexanes/1.9-x g in 90 mL of water
5 = 3x/1.9-x
x = 1.2 g
1.9-1.2 g = 0.7 g of the compound in the water, therefore:
K = 5 = x g in 30 mL hexanes/0.7-x g in 90 mL of water
5 = 3x/0.7-x
x = 0.44 g
Next, add the numbers in bold: 3.1 + 1.2 + 0.44 g = 4.74 g.
6. Which of the following compounds could be separated by acid-base extraction?
a) (/) b) (/) c) (X) d) (X) e) (/)
7. You have prepared an organic compound by reacting it with strong aqueous acid. The work-up
calls for extraction into methylene chloride, then a wash with 5% NaHCO3. What is the purpose
of the NaHCO3 wash?
Washing the organic layer with NaHCO3 helps to decrease the solubility of the organic
layer into the aqueous layer. This allows the organic layer to be separated more easily.
8. What can you do if you do not know which layer is which in an extraction procedure?
Drop a small amount of water into the neck of the separatory funnel. if it remains in the
upper layer, that layer is the aqueous layer.
1. Zhang, Q., Lin, L., & Ye, W. (2018, April 17). Techniques for extraction and isolation of
natural products: a comprehensive review. Chinese Medicine.
2. BSCH 1212 - Practical 4 (2020-12-01 at 22:29 GMT-8). (2020, December 2). Google
Drive. https://drive.google.com/file/d/1v2Y4ez6u4U0k67mffVWk2DYGEJ4iEzj2/view
3. Extraction - Hyfoma.com. (n.d.). Http://Www.Hyfoma.Com/En/Content/Processing-
Technology/Separation-Techniques/. Retrieved December 8, 2020, from
4. Liquids - Densities. (n.d.). Engineering Tool Box. Retrieved December 8, 2020, from