1. what is the minimum volume of boiling water needed to dissolve .2 g of sodium
ID: 818908 • Letter: 1
Question
1. what is the minimum volume of boiling water needed to dissolve .2 g of sodium benzoate? the olubility of sodium benzoate in boiling water is 1 gram per 1.4 mL. about how much sodium benzoate at 25 C is 1 gram per 1.8 mL. Calculate the max mass of solid sodium benzoate that can be recovered when the cooled solution is filtered.
2. why would mixed solvents be used for recrystallization?
3. explain why the melting point of pure phthalic acid is higher than that of pure naphthalene, when both have nearly the same weight.
Explanation / Answer
1. At boiling point:
Volume of water required to dissolve 1 g of sodium benzoate = 1.4 mL
Volume of water required to dissolve 0.2 g of sodium benzoate = 0.2/1 x 1.4
= 0.28 mL
At 25 deg C:
Mass of sodium benzoate dissolved in 1.8 mL of water = 1 g
Mass of sodium benzoate dissolved in 0.28 mL of water = 0.28/1.8 x 1
= 0.156 g
Mass of sodium benzoate recovered = 0.200 - 0.156
= 0.044 g
2. Mixed solvents can be used to increase the solubility of impurities while decreasing the solubility of the compound of interest
=> decreases contamination and increases the recovery yield of the compound of interest
=> increases the efficiency of the recrystallization
3. Phthalic acid is a polar compound with O-H bonds while naphthalene is a non-polar compound
=> intermolecular forces in phthalic acid (hydrogen bonding, dipole-dipole interactions and dispersion forces) are stronger that those in naphthalene (dispersion forces only)
=> more energy required to break intermolecular bonds in phthalic acid for melting
=> phthalic acid has higher melting point
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