Acid-Base Extraction: Benzoic Acid Two-Base Extraction

1901 Words Mar 9th, 2013 8 Pages
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
…show more content…
Compound

benzoic acid
2-naphthol
naphthalene
NaHCO3

NaOH

Mol. Wt. M.P.
(amu)
(˚C)
122.12 123
144.17 123
128.06
80
--
--

--

pKa

4.17
9.5
ntrl.
6.37
(H2CO3)
15.7
(H2O)

--

Water Sol.

(g/100mL, 25 ˚C)

Appearance

0.34 wht. pwd.
0.074 wht./brwn. pwd.
0.0031 clr./brwn. pwd.
--
--

--

TABLE 1 Table of reagents.

The aqueous bicarbonate extract containing the benzoic acid was acidified drop-wise

with 3M hydrochloric acid until a blue litmus paper test turned pink. The solution was swirled

while the acid was being added to allow the carbon dioxide gas formed to dissipate. The

aqueous sodium hydroxide extract containing the 2-naphthol was acidified as described above,

except the extract was chilled in an ice bath both prior and during the acidification process to

prevent the 2-naphtol from turning to an oil. Both of the acidified aqueous extracts were chilled

in an ice bath and the precipitates were individually isolated using a Büchner funnel with pre-

weighed filter paper. Both the benzoic acid and 2-naphthol were rinsed with cold distilled water

and they were allowed to dry for a week.

The ether solution containing the naphthalene was decanted into a pre-weighed, 100mL,

round-bottom flask. A rotary evaporator was used to pull off the ether. The naphthalene was

weighed and transferred to a vial to dry for a week.

The mass of the benzoic acid and 2-naphthol were recorded after a week of air-drying.

Melting points

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