020611 - CHEM 31.1 - Liquid – Liquid Extraction of Benzoic Acid (UNEDITED)

Liquid – Liquid Extraction of Benzoic Acid

Chem 31.1 LEONG and LUKBAN – H. CHIU - 2011

{introduction}

Liquid-liquid extraction method to separate a substance liquid as an extracting solvent

Based on: Solubility Miscibility Relative density of the two liquids.

The partitioning of solutes: equilibrium process characterized by an equilibrium constant:

the partition coefficient or distribution coefficient constant (Kd)

The partition coefficient tells you what fraction of the

material will partition into each solvent layer!

The objectives of this experiment:

(1) to understand the theory and to develop the skills needed in liquid-liquid extraction(2) to identify the characteristics of an ideal solvent in such process(3) to study the different types of solvents(4)to determine the best possible solvent based on solubility and miscibility(5) to learn how to compute for the partition coefficient or distribution coefficient constant for the extraction

{methodology}

Weigh and

dissolve

(1) Weigh 0.5 g benzoic acid, and transfer to beaker with water.

Filter(2)Filter the

solution with pre-weighed filter

paper!

Dry and weigh

(3) Dry the filter paper and determine benzoic acid left.

Take aliquot

and ether.

(4) Take 20 mL and transfer to separatory funnel and add 10 mL ether.

Mix and relieve

pressure!

(5) Open stop cock, after inverting.

Repeat process.

(6) Until no more pressure builds up.

WAIT. (7) Allow mixture to separate.

DRAIN.(8) Drain off organic

layer, collect with beaker.

HEAT and

WEIGH.

(9) Evaporate organic solvent; determine remaining benzoic acid.

{results}

SOLVENT AMOUNT RECOVEREDPERCENT

RECOVERY

Ether0.03 g (per 20 mL of

filtrate) 0.03 x 5 = 0.15 g55%

Hexane n/a n/a

Acetone n/a n/a

•Best Extracting Solvent: Ether•Amount of benzoic acid in saturated solution:0.54 g•Amount of benzoic acid recovered

in the following extraction solvents:

{discussion}

Good Extracting Power! Oh, yeah!

Immiscible with water!

Density is different

with water!

Good stability and

volatility

Solute dissolves!

{guide questions}

Suppose 20 ml of the saturated benzoic acid

solution was treated with 10% NaOH, which solvent (hexane, acetone, ether) could extract the most of the benzoic acid from the aqueous solution? Explain.

ETHER.

What effect does partial miscibility of the two solvents have on the efficiency of the

extraction?

LESS EFFICIENT.

A substance X can be isolated from its plant

source by solvent extraction. However, a

minor component Y has an appreciable solubility in the solvents that may be used. Given below are the solubilities of X and Y in

different solvents:

SOLVENT T, oC

Solubility in 100 g solvent at 28oC

X Y

Ethyl methyl ketone

80 6 5

Cyclohexane 81 8 2

Benzene 80 5 1.8

CCl4 78 8.75 1.25

Water 100 2 1

Which is the best extracting solvent?

CCl4.

Given a saturated aqueous solution of X and Y and

using 100 mL of solvent in (1), determine the percent recovery of X in a single

extraction.

 Since saturated solution:

Then,  

Therefore,  

Repeat (b) using 50mL of solvent in each of the two successive extractions. Determine the percent

recovery and compare this with (b).

FIRST EXTRACTION:

And,  

So, 

SECOND EXTRACTION: 

Therefore, 

What is the percent recovery of the minor component in a single

extraction using 100 mL of solvent in (a).

Partition coefficient of Y:

Since saturated solution: 

 Then,  

Therefore,  

{conclusion}

{recommendation}

{references}