Question

Why might percent recovery be low during extractions?

A mixture that contains benzoic acid, 4-chloroaniline and naphthalene. The 4-chloroaniline is separated first by extraction with hydrochloric acid.Since no phenolic compound is present in this mixture, two extractions with base solution are not required; thus, the benzoic acid could be separated from the neutral compound by extraction with either aqueous sodium bicarbonate or aqueous sodium hydroxide solution. We have chosen to extract the acidic compound into the aqueous layer using sodium hydroxide.

My percent recovery for 4-chloroaniline= 13% Benzoic acid: 30.2% Naphthalene: 25.2%

Answer 1

The Mixture contains the following components.

1. Benzoic acid (strong acid) 2. 4-chloroaniline ( base) 3. Naphthalene (neutral)

There are various steps involved

(a) Separation of the 4-chloroaniline (an amine) is achieved by extracting the mixture with acid

Ar-NH2 + HCl => Ar-NH³⁺ Cl^-3. Further this salt can be extracted in the aqueos layer

(b) The benzoic acid (a carboxylic acid) is separated upon extraction with base

Ar-CO2H + NaOH => Ar-CO^2-Na⁺⁴.

(c) The Napthalene being neutral will remain in the organic layer.

The percent recovery might be low during extraction because of the following reasons:

1. First and foremost the expermental loss and human error itself plays a key role in any chemistry lab done responsible for low % recovery.

2. % recovery may be too low due to side reactions producing other products that do not precipitate out from the orgnic solvent and move down to the aqueous layer so that we can extract them while seprating two layrs. and cannot be measured with a scale.

3. % recovery may be low because one of the reactants may be only partially soluble and one expects complete solubility at times.

4. Due to the starting product not being 100% pure and is present with any kind of contaminants which cant move down either in organic or aqueos layer when trying to recover.

5. It may be also because the reaction did not reach to the completion. This is because of human error.

6. May be the entire product could not be recrystallized so as to recover it in any of the layer aqueous or organic.