EXP. 6: SEPARATION AND IDENTIFICATION
OF UNKNOWN COMPOUNDS
NAME:
SECTION
LOCKER
FORMAL REPORT
(i) ABSTRACT:
The purpose of this experiment was to isolate two compounds – one acidic and one neutral
– from an unknown mixture and to determine their identity. The two compounds were
separated from each other via liquid-liquid extraction, purified via recrystallization, and
identified by their physical properties including melting points by comparing observed
properties to literature values. The experimental results suggest that the acidic compound
is stearic acid, observed to have a melting point of 68.50C – 70.30C and the neutral
compound could be triphenylmethanol or O-Nitrobenzamide, observed to have a melting
point of 160.10C – 161.20C.
(ii) EXPERIMENTAL:
Liquid-liquid extraction was first done on the unknown mixture with the procedures from
CHEMISTRY 235 Lab Manual 2010-2011 pages 2-7 to 2-8. However, 10% NaOH(aq) was
used instead of 10% HCl(aq) and concentrated HCl(aq) was used instead of 6M NaOH(aq) (see
Extraction Flow Chart below). The extraction solvents used were diethyl ether and 10%
NaOH(aq), chosen by performing solubility tests (see Solubility Tests under RESULTS AND
CALCULATIONS below). The separated compounds were then purified via recrystallization
based on the procedures in CHEMISTRY 235 Lab Manual 2010-2011 pages 3-7 to 3-8. For
recrystallization of the acidic compound, a solvent pair was created using the procedure
from CHEMISTRY 235 Lab Manual 2010-2011 page 6-3. After drying, melting point
analysis of the two purified compounds were performed using the Fisher-Johns melting
point apparatus and procedures from CHEMISTRY 235 Lab Manual 2010-2011 pages 4-8 to
4-9. Two trials were performed for melting point analysis of each sample.
CHEMICAL HAZARDS AND WASTE DISPOSAL
Chemical
Diethyl ether
10% HCl(aq)
10% NaOH(aq)
Conc. HCl(aq)
5% NaHCO3 (aq)
Na2SO4 (s)
Ethanol
Chemical Hazards
Flammable, irritant
Corrosive
Corrosive
Very corrosive
Irritant
Use caution
Flammable, irritant
Waste disposal
Liquid organic waste
Wash down sink
Wash down sink
Wash down sink
Wash down sink
Solid waste
Liquid organic waste
Petroleum ether
Very flammable
Stearic acid
Use caution
Triphenylmethanol Use caution
Liquid organic waste
Solid waste
Solid waste
(iii) RESULTS AND CALCULATIONS:
Code Number: 3024
Physical Properties:
(a) Unknown Mixture:
White, fine, crystalline powder. Became clear when dissolved (in diethyl ether).
(b) Final “Acid” Product:
Formed white, silvery plate-like crystals after recrystallization. Soluble in ethanol, not
highly soluble in water nor in petroleum ether.
(c) Final “Neutral” Product:
Formed white needle-like crystals after recrystallization. Soluble in ethanol at high
temperatures, soluble in petroleum ether, not highly soluble in water.
Solubility Tests:
(a)
Test on Mixture for Liquid-Liquid Extraction:
Solvent
Observations
Conclusions
Diethyl Ether
-Schlierien lines present
-everything dissolved after a
while
-nothing happened, powder
did not dissolve
-nothing happened, powder
did not dissolve
-Schlierien lines present
-some of the mixture
dissolved, but some did not
-good to use for the organic
solvent to dissolve the
neutral compound
-not good as extraction
solvent
-not good as extraction
solvent
-good to use as the aqueous
solvent to dissolve the acid
since the base will most
likely deprotonate the acid
and make it more soluble
-since bubbles are released,
not good for extraction
because pressure would
build up
Water
10% HCl
10% NaOH
5% NaHCO3
-Schlierien lines present
-some of the mixture
dissolved, but some did not
-bubbles were present
Extraction Flow Chart:
(I drew this by hand)
Solubility Tests for Recrystallization:
(i) “Acid” Unknown:
Solvent
Room Temperature
Heated
Water
-does not dissolve
everything
-does not dissolve
everything
Ethanol
-dissolves everything
-dissolves everything
Petroleum Ether
-does not dissolve
everything
-does not dissolve
everything
Solvent(s) Selected: Ethanol
(ii) “Neutral” Unknown:
Solvent
Room Temperature
Heated
Water
-does not dissolve
everything
-does not dissolve
everything
Ethanol
-does not dissolve
everything
-dissolves everything
Petroleum Ether
-dissolves everything
-dissolves everything
Solvent(s) Selected: Ethanol
Melting Points:
M.P. Apparatus No.: 34
Calibration Equation(s): y = 0.99X + 1.9
(i) “Acid” Unknown:
TRIAL
T1 (Obs.)
T2 (Obs.)
T1 (Cal.)
T2 (Cal.)
No. 1
No. 2
No. 3
67.90C
68.50C
N/A
69.10C
69.00C
N/A
69.10C
69.70C
N/A
70.30C
70.20C
N/A
ii) “Neutral” Unknown:
TRIAL
T1 (Obs.)
T2 (Obs.)
T1 (Cal.)
T2 (Cal.)
No. 1
No. 2
No. 3
158.50C
159.20C
N/A
159.20C
160.20C
N/A
158.80C
159.50C
N/A
159.50C
160.50C
N/A
Weights:
Weight of original sample = 1.40 g
Weight of final “acid” sample = 0.40 g
Weight of final “neutral” sample = 0.45 g
Percentage recovery = 60.7%
(0.40 + 0.45)g / 1.40 g * 100% = 60.7%
(iv) DISCUSSION:
From the results shown above, it can be deduced that the acidic compound that was
in the unknown sample is most likely stearic acid. Using melting point analysis, the acidic
compound was found to have a melting point of 69.70C – 70.20C, which is consistent with
the literature melting point of stearic acid which is 700C.
It was found that the melting point of the neutral compound was 159.50C – 160.5 0C,
but this does not precisely match the melting point of any neutral compound on the list of
possible neutral compounds. The neutral compound is most likely one of
Triphenylmethanol or o-Nitrobenzamide. The neutral compound formed white needles
and is soluble in ethanol and petroleum ether but not water. This is consistent with the
literature information for o-Nitrobenzamide. However, the melting point temperature is
closest to that of triphenylmethanol which has a melting point literature value of 164.20C.
LABELS FOR TWO UNKNOWNS:
Name:
CHEM 235 Lab Section:
Locker number:
Date:
Weight: 0.40 g
Compound Name: Stearic acid
Structure:
Melting point: 69.70C – 70.20C.
Name:
CHEM 235 Lab Section:
Locker number:
Date:
Weight: 0.45 g
Compound Name: Triphenylmethanol
Structure:
Melting point: 159.50C – 160.50C.