Acid-Base Extraction: Benzoic Acid Two-Base Extraction
TWO-BASE EXTRACTION OF BENZOIC ACID, 2-NAPHTHOL, AND NAPHTHALENE
FROM UNKNOWN SAMPLE # 131
Douglas G. Balmer
(T.A. Mike Hall)
Dr. Dailey
Submitted 11 July 2007
Introduction: The purpose of this experiment was to separate a sample of benzoic acid, 2-
naphthol, and naphthalene of unknown proportions using a two-base extraction method. The
three components of the mixture will react differently to sodium bicarbonate and sodium
hydroxide because each of the bases’ conjugate acids has a different pKa. The pKa’s of benzoic
acid and 2-naphthol are 4.17 and 9.5, respectively, while naphthalene is a neutral compound.
Since benzoic acid is much more acidic than 2-naphthol, the weak base, sodium bicarbonate, will
be able to effectively remove benzoic acid’s acidic hydrogen. It will take the much stronger
base, sodium hydroxide, to remove the hydroxide hydrogen from 2-naphthol. Both of the
sodium salts formed from the base extractions will be soluble in water, while naphthalene will
only be soluble in the original solvent, diethyl ether. Introducing the two sodium salts to
hydrochloric acid will effectively replace the original proton benzoic acid and 2-naphthol lost.
In a chilled environment, both compounds will not be soluble in water, because the solubility of
benzoic acid and 2-naphthol in water at 25˚C is 0.34g/100mL and 0.074g/100mL, respectively.
They can be removed using vacuum filtration. After extraction and purification, the percent
recovery and percentage composition of the unknown sample will be able to be calculated.
The unknown sample may not be separated using melting points because both benzoic
acid and 2-naphthol have a melting point of 123˚C. The purity of the samples will be indicated
by their melting points ranges. The purer the sample, the narrower the melting point range.
Experimental Procedure (Fig.1): An unknown sample of benzoic acid, 2-naphthol, and
naphthalene (Table 1) was massed and the unknown number was recorded. The
FROM UNKNOWN SAMPLE # 131
Douglas G. Balmer
(T.A. Mike Hall)
Dr. Dailey
Submitted 11 July 2007
Introduction: The purpose of this experiment was to separate a sample of benzoic acid, 2-
naphthol, and naphthalene of unknown proportions using a two-base extraction method. The
three components of the mixture will react differently to sodium bicarbonate and sodium
hydroxide because each of the bases’ conjugate acids has a different pKa. The pKa’s of benzoic
acid and 2-naphthol are 4.17 and 9.5, respectively, while naphthalene is a neutral compound.
Since benzoic acid is much more acidic than 2-naphthol, the weak base, sodium bicarbonate, will
be able to effectively remove benzoic acid’s acidic hydrogen. It will take the much stronger
base, sodium hydroxide, to remove the hydroxide hydrogen from 2-naphthol. Both of the
sodium salts formed from the base extractions will be soluble in water, while naphthalene will
only be soluble in the original solvent, diethyl ether. Introducing the two sodium salts to
hydrochloric acid will effectively replace the original proton benzoic acid and 2-naphthol lost.
In a chilled environment, both compounds will not be soluble in water, because the solubility of
benzoic acid and 2-naphthol in water at 25˚C is 0.34g/100mL and 0.074g/100mL, respectively.
They can be removed using vacuum filtration. After extraction and purification, the percent
recovery and percentage composition of the unknown sample will be able to be calculated.
The unknown sample may not be separated using melting points because both benzoic
acid and 2-naphthol have a melting point of 123˚C. The purity of the samples will be indicated
by their melting points ranges. The purer the sample, the narrower the melting point range.
Experimental Procedure (Fig.1): An unknown sample of benzoic acid, 2-naphthol, and
naphthalene (Table 1) was massed and the unknown number was recorded. The