Q1) Consider a crystallization of sulfanilamide in which 10mL of hot 95% ethyl a

Question

Q1) 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 students have to do at this point to make the crystallization work without restarting the experiment?

Q2) Water and hexane are immiscible liquids. Acetone and water are miscible. Acetone and hexane are miscible. Explain how this is possible. (Is this a case of like dissolves like? )

Explanation / Answer

1) You haven't been able to form a nucleus around which crystallization can occur. This if very common in new labs, where the condtions are relatively pristine. Old labs have more things floating around.

Your scratching didn't work. Bummer.

So, your volume still may be too high. You want to concentrate it down to at least half volume. And you really want crystallization to start from warm solution. Slow crystallization from warm solution gives the best results.

2)Regarding intermolecular forces, acetone has the chemical formula C3H60, through Hydrogen Bonds, the partial positive charge of Hydrogen in acetone is attracted to the partial negative charge of Oxygen in water. Also, inversely the Hydrogen in water is attracted to the Oxygen in Acetone. A dipole-dipole bond is also formed between the two substances due to the difference in charges. They there fore have an affinity for one another, and to be separated (as an example through fractional or simple distillation) the dipole dipole bonds and hydrogen bonds would need to be broken.

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