Question

In: Chemistry

1) When the percent recovery is less than 100%, where is most of the uncovered material...

1) When the percent recovery is less than 100%, where is most of the uncovered material and how might you go about recovering it if you needed to? (three of fewer sentences)

2) Hot filtration was not necessary in the recrystallization of phthalic acid but was necessary in the recrystallization of naphthalene. Why was it necessary in the recrystallization of naphthalene?

Both of these are about a recrystallization experiment.

Solutions

Expert Solution

1) Most losses during recrystallization occur when doing the filtration, because when washing the crystals with the solvent, the solvent dissolves a portion of the crystals. This can be avoided by a second process of crystallization of the washing solvent.

2) Hot filtration is necessary in the recrystallization of naphthalene because the solubility of naphthalene increase with the temperature.

The solubility of naphthalene change depending on the solvent but in all cases, the solubility increase significantly with increasing temperature

For example, the solubility of naphthalene in water at 25°C is 31.6mg/L and the solubility of phthalic acid in water at 25°C is 6000mg/L (0.6g/mL), which means phthalic acid is much more soluble in water at 25°C.

Also, when increase the temperature, the solubility of naphthalene in water, increase as following:

19 mg/L (10 °C)

31.6 mg/L (25 °C)

43.9 mg/L (34.5 °C)

80.9 mg/L (50 °C)

238.1 mg/L (73.4 °C)


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