Post Lab
Solubility, Crystallization and Melting Point Determination Post-Lab
Discussion Guidelines:
Part 2A and 2C: Draw tables (as in textbook) showing which combinations were soluble/miscible and which were insoluble/immiscible. Explain why this is so. Why are certain chemicals soluble/miscible when others are not?
Part 3A: Calculate % recovery (this is not the same as % yield – see handout from the first day of lab if you’re confused), and determine melting point of your product. Discuss % recovery, if it’s reasonable (high or low and the pros and cons for both), possible sources of loss, etc. Also discuss your melting point; compare it with the literature melting point and the melting point of the impure starting material. Overall, based on these results, how successful was your crystallization and why?
Post-lab Questions:
1. For the following pairs of solutes and solvent, predict whether the solute would be soluble or insoluble. It may be helpful to look up some of the chemical structures. (3pts) a. Malic acid in water b. Naphthalene in water c. Amphetamine in ethyl alcohol d. Aspirin in water e. Succinic acid in hexane f. 1-Decanol (n-decyl alcohol) in water
2. Predict whether the following pairs of liquids would be miscible or immiscible. It may be helpful to look up some of the chemical structures. (3pts) a. Benzene and water b. Water and methyl alcohol c. Hexane and benzene d. Methylene chloride and benzene e. Water and toluene f. Ethyl alcohol and isopropyl alcohol
3. Consider a crystallization of sulfanilamide in which 10mL of hot 95% ethyl alcohol is added to 0.10g of impure sulfanilamide. After the solid has dissolved, the solution is cooled to room temperature and then placed in an ice-water bath. No crystals form, even after scratching with a glass rod. Explain why this crystallization failed. What would you have to do at this point to make the crystallization work
Discussion Guidelines:
Part 2A and 2C: Draw tables (as in textbook) showing which combinations were soluble/miscible and which were insoluble/immiscible. Explain why this is so. Why are certain chemicals soluble/miscible when others are not?
Part 3A: Calculate % recovery (this is not the same as % yield – see handout from the first day of lab if you’re confused), and determine melting point of your product. Discuss % recovery, if it’s reasonable (high or low and the pros and cons for both), possible sources of loss, etc. Also discuss your melting point; compare it with the literature melting point and the melting point of the impure starting material. Overall, based on these results, how successful was your crystallization and why?
Post-lab Questions:
1. For the following pairs of solutes and solvent, predict whether the solute would be soluble or insoluble. It may be helpful to look up some of the chemical structures. (3pts) a. Malic acid in water b. Naphthalene in water c. Amphetamine in ethyl alcohol d. Aspirin in water e. Succinic acid in hexane f. 1-Decanol (n-decyl alcohol) in water
2. Predict whether the following pairs of liquids would be miscible or immiscible. It may be helpful to look up some of the chemical structures. (3pts) a. Benzene and water b. Water and methyl alcohol c. Hexane and benzene d. Methylene chloride and benzene e. Water and toluene f. Ethyl alcohol and isopropyl alcohol
3. Consider a crystallization of sulfanilamide in which 10mL of hot 95% ethyl alcohol is added to 0.10g of impure sulfanilamide. After the solid has dissolved, the solution is cooled to room temperature and then placed in an ice-water bath. No crystals form, even after scratching with a glass rod. Explain why this crystallization failed. What would you have to do at this point to make the crystallization work