Crystallization - Techniques in Organic Chemistry

Crystallization is a common method to purify substance in a laboratory. We let a substance dissolves into a hot solvent, and let the solution cool down slowly to crystallize the substance out. In the process, the substance forms lattices orderly, but the impurities could not crystallize with the substance that is because different substance has different structure of lattices, so impurities tend to remain in solution.

Acetanilide is crystallizing from hot water

Experimental Process

In this experiment, we have two sub-experiments to do.

a. Acetanilide + Methylene blue(as impurity)
b. Acetanilide + Methylene blue(as impurity) ; use decolorizing carbon to absorb impurities

Experiment without decolorizing carbon:

1.      Weight 1.000g acetanilide in to a 50ml-flask. 

 Acetanilide before crystallization

2.      Pour 20ml water and put the stir bar into to the flask.

3.      Boil the solution on a hot plate until acetanilide are all dissolved.

 Acetanilide totally dissolved in hot water

4.      Add some drops(~2.0ml) of methylene blue.

5.      Take the flask from the hot plate and let the solution cool down to about 50℃.

6.      Put the flask into ice bath to crystallize acetanilide out.

 Solution in ice bath

7.      Whip the smoothie (water and acetanilide) and filtrate it through vacuum filtration.

 Vacuum filtration apparatus(Büchnertrichter)

8.      Air-dry the final product.

9.      Calculate the recycling efficiency.

Experiment with decolorizing carbon:

1.      Weight 1.000g acetanilide in to a 50ml-flask.

2.      Pour 20ml water and put the stir bar into to the flask.

3.      Boil the solution on a hot plate until acetanilide are all dissolved.

4.      Add some drops(~2.0ml) of methylene blue.

5.      Take the flask from the hot plate and let the solution cool down to about 50℃.

6.      Add some (~0.02g) decolorizing carbon into the flask.

 Decolorizing carbon in solution

7.      Boil the solution again.

8.      Use hot filtration to separate decolorizing carbon from the solution and collect the solution into a new flask.

 Hot filtration apparatus

9.      Take the flask from the hot plate and let the solution cool down to about 50℃.

10. Boil the solution to condense it to 20mL

11.  Put the flask into ice bath to crystallize acetanilide out.

12.  Whip the smoothie (water and acetanilide) and filtrate it through vacuum filtration.

13.  Air-dry the final product.

14.  Calculate the recycling efficiency.

Experimental Record

Experiment without decolorizing carbon	Acetanilide (g)	1.020
	Filter paper (g)	0.200
	Methylene blue (ml)	2.0
	Final weight of acetanilide(g)	0.770
	Recycling efficiency (%)	75.5
	M.P. of acetanilide (℃)	113.0~114.0

Experiment with decolorizing carbon	Acetanilide (g)	1.010
	Filter paper (g)	0.180
	Methylene blue (ml)	2.0
	Decolorizing carbon (g)	0.030
	Final weight of acetanilide(g)	0.850
	Recycling efficiency (%)	84.2
	M.P. of acetanilide (℃)	114.0~115.0

 Product A: Without using decolorizing carbon. Still a little grayish.

 Product B: Using decolorizing carbon. With higher purity.

 

Analysis

		Percentage of error
Melting point of pure acetanilide (℃)	114.3	N/A
Melting point of acetanilide (without decolorizing carbon) (℃)	113.0~114.0	0.7 %
Melting point of acetanilide (with decolorizing carbon) (℃)	114.0~115.0	0.2%

 By testing melting points, we can also proof the purity of product B is higher than product A.

Homemade Charcoal Pencils by Dry Distillation

Dry distillation is a method to make charcoal and some combustible gases, it is also called coal gas. The main idea of this method is "heat a solid material to decompose lager molecules into smaller molecules". In the end, fiber carbon would leave.

 A charcoal pencil made by dry distillation.

Material:

1. Bamboo chopsticks
2. Charcoal
3. Furnace
4. Aluminum foil

Step 1: Wrap bamboo chopsticks with aluminum foil

Don't put too many chopsticks at the same time.

Leave a vent to release combustible gas out

Step 2: Put the package into burning charcoal

Burn the package continuous, until there are no more gas release from the vent.

Step 3: Get charcoal pencils

Homemade charcoal pencils

 Homemade charcoal pencils

 Ha ha~~ I drew the structural formula of TNT.

 There were some tar stick at the Al foil which looks like rainbow.

 

Use a Melting Point Apparatus to Figure Out Eutectic Point

Melting point apparatus  is an instrument used to measure melting point of substance. In this experiment, we were going to measure the melting points of different components, and figure out the eutectic point by using polynomial fitting.

Fisher-Johns apparatus

Observing through the lens

Melting point apparatus

Experimental record

Component	Melting range (℃)	Average (℃)
100% Benzoic acid	122.0~124.0	123.0
99% Benzoic acid + 1%  2-naphthol	118.0~120.0	119.0
80% Benzoic acid + 20%  2-naphthol	90.4~113.6	102.0
50% Benzoic acid + 50%  2-naphthol	90.2~106.5	98.4
20% Benzoic acid + 80%  2-naphthol	88.3~105.8	97.1
100% 2-naphthol	120.0~122.0	121.0

Data processing

Model	Polynomial
Adj. R-Square	0.91129	0.99865	0.98503
		Value	Standard Error
Poly. fitting of Max.	Intercept	122.42316	1.75243
Poly. fitting of Max.	B1	-70.83259	42.35292
Poly. fitting of Max.	B2	179.32579	205.90115
Poly. fitting of Max.	B3	-294.68184	325.2792
Poly. fitting of Max.	B4	185.78141	161.53845
Poly. fitting of Min.	Intercept	121.58944	0.45627
Poly. fitting of Min.	B1	-325.07157	11.02727
Poly. fitting of Min.	B2	1139.85131	53.6097
Poly. fitting of Min.	B3	-1644.22212	84.69171
Poly. fitting of Min.	B4	827.85708	42.05916
Poly. of average	Intercept	122.00714	1.10342
Poly. of average	B1	-198.13952	26.66762
Poly. of average	B2	660.78879	129.64618
Poly. of average	B3	-970.95412	204.81286
Poly. of average	B4	507.30774	101.71309

Analysis

Poly. of average	F(x) = y = 122.00714-198.13952*x+660.78879*x^2 -970.95412*x^3+507.30774*x^4
First order derivative of F(x)	y’ = -198.13952+1321.57758*x -2912.86236*x^2+2029.23096*x^3
Eutectic point (Benzoic acid / Total)	0.717
Eutectic temperature (℃)	95.8