Experiment 1: Solubility
1/29/09 Drew Frerking
Benzoic Acid in Acetone

Solute: Benzoic Acid
SMILES: O=C(O)c1ccccc1
Type: aromatic carboxylic acid
Chemspider link: http://www.chemspider.com/238

Solvent: Acetone
SMILES: O=C(C)C
Type: ketone
Chemspider link: http://www.chemspider.com/175

Other solvent info:
Molecular formula: C3H6O
Molar mass: 58.08 g/mol

InChI: InChI=1/C3H6O/c1-3(2)4/h1-2H3

Density: .79g/ml
Melting point: -94.9 °C
Boiling Point: 56.53 °C
Safety Info: Flammable, irritant to skin and eyes, in large quantities may depress CNS
Procedure

1. A sample of 20mL in total of acetone was poured into a 200mL beaker. Hexane was not used as it was discovered that it would be difficult to dissolve benzoic acid. To this 30mL of acetone using a small spatula benzoic acid was added until the solution became supersaturated and recrystalization ocured. This required a fairly large amount of benzoic acid (approximately 20 spatula’s worth). The solution was swirled in the beaker to facilitate mixing.
Note: The solution seemed to evaporate rather rapidly. Upon crystallization almost no liquid remained in the mixing vessel. Therefore about 10mL was added to the solid. It was this volume that was then used throughout the experiment.

2. Clarification of the saturated solution (via centrifugation)
Next, about 3mL of the solution from the beaker was added to each centrifuge tube. Four tubes were used in total. Once added place the four centrifuge tubes in the centrifuge (making sure to align them evenly to facilitate even spinning of the centrifuge). Centrifugation took place for one minuet.

3. Determining the volume of the saturated solution
After centrifuging, the volume from each centrifuge tube was approximated using 1mL pipettes. It was found that about 3mL remained in each.

4. Obtaining the mass of the evaporation vessel
The mass of four evaporation vials were measured and are listed in the table below.

5. Initial mass of the solutions
To each beaker the solution was added and then weighed again to obtain the mass of the four solutions before evaporation.

6. Initial evaporation of solvent
One large beaker and one small beaker were filled water for a hot water bath and heated on a hot plate. For spatial reasons three of the vials were added to the large beaker and the final to the smaller beaker. They were allowed to evaporate. The process took approximately 5 minuets. The water was at a rolling boil around 100 C. Each vial solidified rapidly at the same point relatively.

7. Obtaining the mass of the evaporation of solute and vessel

8. Next the beakers were then weighed again. The difference in mass was noted. Prolonged evaporation. The solid was allowed to dry overnight and readings were taken again. The original masses were used in the calculations because the mass after prolonged evaporation differed by only a very small amount. They are recorded as:
1.) 13.25g
2.) 13.43g
3.) 13.19g
4.) 13.37g
Table of Results and Calculations:

Trial 1
Trial 2
Trial 3
Trial 4
Solute
Benzoic Acid
Benzoic Acid
Benzoic Acid
Benzoic Acid
Solvent
Acetone
Acetone
Acetone
Acetone
Solvent density
.79 g/cm3
.79 g/cm3
.79 g/cm3
.79 g/cm3
Mass of Empty evaporation vessel (g)
12.831
12.861
12.817
12.846
Volume of Solution (g)
3.0ml
3.0mL
3.0mL
3.0mL
Mass of evaporation vessel + solution (g)
14.300
14.594
14.00
14.483
Mass of evaporation vessel +solute (g)
13.298
13.438
13.199
13.402
Solubility g/mL using volume of solution*
.156
.190
.127
.185
Concentration M (mol/L)*
1.27
1.57
1.03
1.52
Molality in moles/kg using mass of solution*
1.60
1.98
1.31
1.94
Solubility g/100g solvent using mass of solution*
31.8
33.3
32.3
34.0
[Value was marked at "DONOTUSE" because to insufficient conditions to form a saturation solution JCB]



















  • Denotes calculations are shown below
Solubility: (g solute/mL solution)

1. grams solute: (Mass of evaporation vessel + solute) – Mass of empty evaporation vessel
Trial 1: 13.298g-12.831g=.467g
Trial 2: 13.438g-12.861g=.577g
Trial 3: 13.199g-12.817g=.382g
Trial 4: 13.402g-12.846g=.556g
2. Solubility:
Trial 1: .467g/3mL solution= .156
Trial 2: .577g/3mL solution= .190
Trial 3: .382/3mL solution= .127
Trial 4: .556g/3mL solution .185

Concentration in mol solute/L solution:

1. (.467g/3mL) (1mol/122.12g)=.0038mol/.003L=1.27
2. (.577g/3mL) (1 mol/122.12g)= .0047mol/.003L=1.57
3. (.382/3mL) (1 mol/122.12g)= .0031mol/.003L=1.03
4. (.556g/3mL) (1 mol/122.12g)= .0046mol/.003L=1.52

Molality: mol solute/kg solvent

1. .0038mol/(3ml x.79) x (1000g/1kg)=1.60
2. .0047mol/(3ml x .79) x (1000g/1kg)=1.98
3. .0031mol/(3ml x .79) x (1000g/1kg)= 1.31
4. .0046mol/(3ml x .79) x (1000g/1kg)= 1.94

Solubility: g solute/100g solvent
1. (.467g x 100)/1.469g soln= 31.8g/100g
2. (.577g x 100)/1.733g soln= 33.3g/100g
3. (.382g x 100)/ 1.183g soln= 32.3g/100g
4. (.556g x 100)/ 1.637g soln= 34.0g/100g