Pre-Laboratory Questions-EXP 3 Name: Due before lab begins. Answer in space prov
ID: 556492 • Letter: P
Question
Pre-Laboratory Questions-EXP 3 Name: Due before lab begins. Answer in space provided. 1. What is the ideal solvent for crystallization of a particular compound? What is the primary consideration in choosing a solvent for crystallizing a compound? 2. Impure benzoic acid was dissolved in hot water. The container of solution was placed in an ice-water bath instead of being allowed cooling slowly. What will be the result of cooling the solution in this manner? 3. Outline the successive steps in the crystallization of an organic solid from a solvent and state the purpose of each operation. 4. Compound X is quite soluble in toluene, but only slightly soluble in petroleum ether. How could these solvents be used in combination in order to recrystallize X? 5. 0.12 g of compound "Y" dissolves in 10 ml of acetone at 25 oC and 0.85 g of the same compound dissolves in 10 ml of boiling acetone. What volume of acetone would be required to purify a 5.0 g sample of compound?Explanation / Answer
Characteristics of a good solvent:
1 . doesn't react or form solvated molecules.
2. Dissolves compound with a solubility difference with temperature.
3. Is easily removed from crystals by washing or evaporation.
Selecting a Solvent
If the solvent is not specified, you will need to test a variety of solvents to determine what will work best for the solute you are trying to recrystallize. This testing can be accomplished by putting a small amount of your solute (about the size of a pea) into three small test tubes. In each test tube, place 0.5 mL of each potential solvent. Use a stirring rod to agitate the solute or "flick" the bottom of the test tube with one finger while holding the top with the other hand. If the solute dissolves at room temperature with stirring, the solvent should be discarded as a potential recrystallization solvent. If the sample does not dissolve at room temperature, place the test tube in a hot water bath and stir the contents. If the solute partially dissolves add more solvent and continue stirring. If the solute dissolves completely, remove it from heat and place it in an ice-water bath. If crystals do not form, try to scratch the inside of the test tube with a stirring rod. If crystals form, you have found an appropriate recrystallization solvent; if no crystals form, keep looking for the right match between solvent and solute.
Only one question will be answered at a time as per Chegg policy.
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.