Question

pre-laboratory Questions A

1 Explain why it is more efficient to make several extractions using small portions rather than one extraction using the same total volume.

2 Define the following terms:

Drying agent intensity

Drying agent capacity

3 Select the upper layer in each pair of mixed solvents (see Appendix C):

Water and benzene

Water and carbon tetrachloride

Water and ether

4 Write an equation for the reaction of a benzoic acid with aqueous sodium bicarbonate.

5 Complete the following table:

compound                                         capacity                                      intensity

MgSO₄

Na₂SO₄

CaCl₂

K₂CO₃

Pre-laboratory Questions B

1 Define the term “distribution coefficient.”

2 Write an equation to describe the method of converting a water-insoluble organic acid into a water-soluble salt.

3 During the process of using a separatory funnel an emulsion is occasionally formed. How may the emulsion be “broken?”

4 Complete the following table:

compound                                         capacity                                      intensity

MgSO₄

Na₂SO₄

CaCl₂

K₂CO₃

5 Outline a scheme, using a separatory funnel, to separate a solid mixture of a water-insoluble organic base and a water-insoluble neutral compound.

6 What is the IUPAC name for methylene chloride?

Answer 1

Multiple extractions with small quantities of solvent or solution are more efficient than one extraction using the same amount of solvent. The amount of material left behind after two or three extractions is usually very small and does not justify the effort and resources . Excessive washing will also lower the yield of the product, if the desired compound dissolves noticeably in the other phase. It is usually takes several extractions to remove all the solute from solvent because not all the solute can be transferred to solvent in a single extraction. It is always a good idea to use several small portions of the second solvent rather than to make a single extraction with a large portion

Drying agent intensity: It measure the efficiency of intensity that is the degree of dryness attained

Drying agent capacity

It is the capacity refers to the maximum numbers of moles of water that the drying agent can bind. Capacity: the amount of water absorbed per unit of mass

Select the upper layer in each pair of mixed solvents :

Water and benzene : benzene float on water

Water and carbon tetrachloride : water float carbon tetrachloride

Water and ether: ether float on water

A partition-coefficient (P) is the ratio of concentrations of a compound in a mixture of two immiscible phases at equilibrium. This ratio is therefore a measure of the difference in solubility of the compound in these two phases

4] EQUATION IS     

C6H5COOH + NaHCO3 ---> NaC6H5COO + H2O(l) + CO2(g)

6]

IUPAC name for methylene chloride is dichloromethane