3. Tell how each of the following experimental errors will affect your ex- perim

Question

3. Tell how each of the following experimental errors will affect your ex- perimental results (yield, purity, or both), and explain why. (a) You failed to dry the product completely. (b) You used enough water to recrystal- lize phenacetin, but your unknown was acetanilide. (c) In the "Extrac- tion and Evaporation" Experiment, you didn't extract all of the aspirin from the dichloromethane solution. Tell whether each of the experimental errors in Exercise 3 will affect the melting point of the unknown component. If it will, tell how it will affect the melting point, and explain why. 4.

Explanation / Answer

1)a) Drying of product is the final step in the synthesis. If the product is incompletely dried the solvent (if water) that is present in the product may increase the contamination as moisture allows microbial growth. The solvent present may also effect the melting point of the compound. So it effect the yield and melting point.

b) In recrystalization the solvent should be selected which is partialy soluble in room temperature and solubility increase with temperature. If water is used to recrystalize phenacetin hot water will dissolve phenacetin as well as acetanilide also so there is a chance of formation of mixture of product. So the yield and purity will also be effected

c) In extraction and evaporation experiment if we dont extract all of the aspirin from the dichloromethane solution. The yield of the product will be decreased. As some amount of product will be remained in the solution.

2)As the experiment 3 in the above case has the chances of presence of impurity it will effect the melting point of the product. Their is decrease in melting points of the product.

if the solid sample is not fully free from the solvent or it has some impurities, the solvent present in the sample reduces the vapour pressure of sample to some extent and the melting point range will be longer. similarly the impurities present in the sample melt at lower temperature than the sample which also increasses the melting point range called melting point depression. The pure compounds have low melting point range.The impure sample or the improperly dry sample finaly show decrease in melting point of sample

Decrease in yield does not effect melting point if the sample is pure.

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