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Solubility book (3rd Edn)
Dominican University Student Project
Type: Carboxylic acid
Mass of evaporation vessel (g)
Volume of solution (mL)
Mass of evaporation vessel and solution (g)
Mass of evaporation vessel and solute (g)
Solubility using volume of solution (g/mL)
Molality (moles/kg) using mass of solution
Solubility (g/100g) using mass of solution
Average Solubility : 17.35 g solute/100g solution
Average Solubility (M): 0.9775 moles/L
ADME stands for absorption, distribution, metabolism and excretion. It describes what happens to a pharmaceutical compound in an organism. It begins with the uptake and ends with the removal of the remaining product and byproduct of reactions in the body. Since the human body is mainly water, the compounds used as medicine have to be soluble in an aqueous environment. The solubility in water is key to understanding and testing new compounds for use in the body. This is one reason why this project is important for basic research.
The non-covalent forces that determine the solubility, or insolubility, of the compound are hydrogen bonding, hydrophobic interactions and Van der Waals forces. These are active in alcohols, in which cinnamic acid is far more soluble than in water. The longer carbon chain in the acid makes it less soluble in water since the central section is hydrophobic. The alcohol dissolves the solute where water does not.
Liquid/liquid solutions are harder to work with because they require the use of boiling points to separate and use condensation to recover either the solute or solvent depending on which has a lower boiling point. Once the liquid is separated, a method to crystallize the solute, or separate by any other means, will be necessary. If the solute is liquid at room temperature, a cold temperature method is necessary.
Order of addition matters when adding acids and water. If water is added to acid it may explode due to a rapid reaction. It is a matter of safety to know which should be added to the other. It also makes a difference in the procedure to determine the saturated solution while using the least amount of supplies and compounds.
Centrifugation is a better choice than filtration, since it will force the excess from a supersaturated solution. The filter may remove more than the supersaturate by physical means. I tested the centrifuge tube by adding water to my sample and found a large amount of cinnamic acid in the tube. This was left in the tube after the process of centrifugation.
Since the sample is dissolved in a liquid, it is not safe to assume that all of the liquid is removed after the initial solvent evaporation in a hot water bath. Since many compounds are soluble in water, it is also possible for water to be in the sample after exposure to the atmosphere. Longer term drying in a hood or a dessicator should generate a sample with less water in it.
A dessicant is a substance that absorbs water. The air moving through the hood or a hygroscopic compound such as silica gel could be used for that purpose.
The sample may weigh more after long term drying, due to picking up oxygen or other atmospheric gas while the sample was exposed to air. Oxygen is a very powerful agent and might react with most of the compounds we are testing.
Accurate is how close the answer is to the actual value. Precise is how repeatable the value is.
The absolute uncertainty of the solubility is ±1.4 mg
The relative uncertainty of the solubility is ±0.04 g
Wednesday, January 28, 2009
A. Making supersaturated solution
1.Obtain mass of weighing plate.
2. Obtain starting mass of Cinnamic acid and weighing plate.
3. Note starting time for experiment.
4.Add Cinnamic acid to 16 mL of methanol while stirring.
5. Continue adding Cinnamic acid until precipitate forms.
6. Obtain final mass of Cinnamic acid and plate.
B. Clarifying Solution
1. Split solution into 4 even volumes.
2. Add aliquots to centrifuge tubes.
3. Spin samples at machine max for 2 minutes. (Longer is solution is opaque.)
4. Obtain mass of 4 evaporation vessels.
5. Carefully decant supernatant into graduated cylinder and record volume.
6. Decant supernatant into evaporation vessels and record mass.
C. Evaporating Solutions
1. Add evaporation vessels to water bath.
2. Continue to heat water bath until methanol begins to boil.
3. Turn down heat and continue to heat until all methanol is evaporated away.
4. Obtain preliminary mass of evaporation vessel and Cinnamic acid.
5. Note ending time of experiment.
6. Leave the open evaporation vessels in the hood for 24 hours and record final mass.
Wednesday, January 28, 2009
Figure 1: Starting supplies. The disposable pipette was calibrated for accurate measurements. Water in 150mL Erlenmeyer flask is for comparison to color of methanol.
Figure 2: Saturated Cinnamic acid methanol solution. Note the color difference and the presence of precipitate on the bottom of the flask.
Figure 3: The evaporation setup. The screw top jars will be used to store the samples after evaporation is complete.
Figure 4: The centrifuge tubes with a precipitate in water after supernatant was removed. This illustrates the effect of the centrifuge process for removing the excess cinnamic acid. The tubes were clear just after the supernatant was decanted.
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