Question

14. (3 pts.) The ionized benzoic acid dissolves better in water than it does in diethyl ether, which is how and why it is extracted into the water phase. Give the most important IMFs that are responsible for solubilizing the benzoic acid anion in the water. Give also the most important IMFs that are responsible for solubilizing the sodium cation in the water. The kinds of strong IMF that could be present are ion-dipole, hydrogen bonding (ignore dipole-dipole and induced dipole, London dispersion forces, in this problem) H-O.

Answer 1

Solution:

Benzoic acid (C6H5COOH) is insoluble in water. The extraction of benzoic acid in aqueous medium is carried out in two steps:

Step 1) Benzoic acid is treated with a strong base like NaOH to form water soluble sodium salt of benzoate anion (C6H5COO-Na+).

C6H5COOH + NaOH = C6H5COO-Na+ + H2O

Step 2) The aqueous solution containing sodium benzoate salt is treated with strong acid like HCl, to extract C6H5COOH.

  C6H5COO-Na+ + HCl =  C6H5COOH + NaCl

Solubilization of benzoate anion:

From the given intermolecular forces of attraction, both ion-dipole and hydrogen bonding are responsible for the solubilizing benzoate anion because negatively charged oxygen ( O-) interacts with H of water by strong ion-dipole interaction while double bonded oxygen (=O) interacts with H of water by intermolecular hydrogen bonding.

Solubilization of Na+ ion:

From the given intermolecular forces of attraction, the ion-dipole interactions are responsible for the solubilizing sodium ion (Na+) because positively charged sodium ion ( Na+) interacts with negative pole of water (O) of water by strong ion-dipole interaction.