4 Recrystallization of Acetanilide In this experiment a sample of impure acetani

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4 Recrystallization of Acetanilide In this experiment a sample of impure acetanilide will be recrystallized from wate acetanilide recrystallizes out as white leaflets from water. You will weigh the crude and the pure product and determine the melting point before and after recrystallizat oalple Pure sample illustrate the efficiency of the process. Caution Boiling water and steam can cause severe buns. Be very careful when handling vessels contain hot water. Macroscale Weigh out a 1.5-g sample of impure acetanilide and use a few milligrams to determine the melting point. Record the melting point on the report sheet. Place the rest of the acetanilide in a 100-mL round-bottomed flask, connect this flask to a reflux condenser (Figure 2.3 a), and start a slow stream of water through the jacket of the condenser. Add 35 mL of water to the flask through the top of the condenser, and bring the water to a boil by heating with a mantle. Adjust the mantle temperature so that the water refluxes steadily. Continue to heat until no more solid appears to dissolve. Then remove the heat source, allow the flask to cool a few moments after reflux stops to avoid boil over, remove the condenser momentarily, and add a small amount (about 0.2 g) of decolorizing charcoal to the contents of the flask (see footnote, p. 12). Replace the condenser and heat the solution at reflux for an additional 5 min. o 2012 Cmpige Leeming All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part

Explanation / Answer

1) the purpose of recrystallization is to purify the primary compound. It is a simpler and dear technology , and does not take much time as compared to chromatographic separation or purification

2) During recrystallization we genrally dissolve the impure compound in hot solvent. The impurities and primary compound get dissolved in it. on cooling the pure compound crystallizes out (separted) and the soluble impurities remains in the solvent

3) Crystallizatio is induced by scratching the glass ware, as due to this some imperfactions are produced on the glass surface of the veseel. These serve as site for nucleation. Nucleation is the first stage of crystal formation. so one nucleus is being formed the rest of crystal grows around it.

4) The recrystallization solvent should be unreactive for the compound to be separated at all temprature for the complete time of recrystallization.

the compound should be soluble in the solvent at high temperature and should not be highly soluble in cold solvent

a) For impurities they should be either highly soluble in solvent at room temprature or should not be soluble in solvent at any temperature.

5) The application of ordinary gravity filteration is when we need filterate for futher assessment.

So vacuum filteration is used when

(i) we need the precipitate for further assessment .

(ii) it requires less time

(iii) it is more effective as we use pressure for filteration

6) As we have discussed in the properties of good solvent for a compound.

The acetanilide is very less soluble in cold water . However its solubility is high when we use hot water.

so on cooling the acetanilide gets precipitated out easily

7) If we will use cold funnel, then acetanilide will gets separated out during filteration only,

It will cause early recrystallization of acetanilide in the funnel.

However if we will use hot funnel then it will not recrystallize early.

8) it is very easy to separate charcoal and sugar from actanilide as

a) acetanilide is soluble in hot water

b) charcoal is insoluble in water at any temperature

c) sugar is soluble in cold water

So we will dissolve impure acetanilide in cold water (sugar gets dissolved), we will heat the water so the acetanilide will get dissolved in it, and the charcoal will remain insoluble.

We will filter off the charcoal by gravitational separation.

then will cool down the water so that acetanilide will recrysallize out

and sugar will remain in the water

9)As for separation of dibromobenzene water and ethanol are not good solvents alone. So to make a good solvent we mix water and ethanol. the turbidity is an indicator of good mixing ratio of the two for recrystallization

10 ) It is due to solubility of water -ethanol and water-hexane

Water and ethanol are soluble in each other.

Water and hexane are insoluble in each other.

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