Question

In an extraction experiment similar to your expt. 4, you attempt to separate 2-naphthol from cyclohexane, both of which are dissolved in ether. You attempt the separation by extracting the organic layer with a ̴5% NaOH (aq) solution (made by adding 5.00 g of NaOH to every 100 mL of water). Assuming that all of the base present in the aqueous solution reacts with the phenol during your extractions, what is the minimum volume of the aqueous NaOH solution needed to deprotonate 20.0 g of 2-naphthol in order to extract it into the water layer? Clearly show all calculations. After removal of the phenol from the ether layer, only cyclohexane would remain. Concisely explain how you could efficiently isolate relatively pure cyclohexane from the ether layer.

Answer 1

CONCEPT: Covert mass of 2-napthol and 5% NaOH to moles. Then calculate the no. of moles of NaOH required to react with 2-naphol.

Solution: The balanced equation of reaction between NaOH and 2-naphthol (C₁₀H₈O) is:

C₁₀H₈O + NaOH ------> C₁₀H₇O^-Na⁺ + H₂O

Moles of C₁₀H₈O = mass of C₁₀H₈O / Molar mass of C₁₀H₈O = 20.0/144.17 = 0.138 moles

Molarity of NaOH solution = (W/M X V) X 1000

W = mass of NaOH = 5g, M = molar mass of NaOH = 40.0g, V = volume = 100mL

= (5/40 X100) X 1000 = 1.25M

We have 0.138 moles of 2-naphthol, it means we need 0.138 moles of NaOH.

Moles of NaoH required = 0.138 = Molarity of NaOH X Volume of NaOH

0.138 = 1.25 X V

V = 0.108L = 108 mL