Question

In what ways can you improve and acid-base extraction procedure for organic chemistry lab?

Our napthalene ended up being contaminated with p-nitroaniline, meaning that we didn't get all of the p-nitroaniline in our HCl extract. We're supposed to come up with two ways to improve the technique.

Answer 1

Acid-base extraction is a type of liquid-liquid extraction depending on varying solubility in aqueous and organic solvents. It is used to separate organic compounds based on acidity and basicity.

By addition/removal of a proton from the organic compound, it can be rendered acidic/basic and hence it becomes ionic. Greater the polarity of the compound, more will be its solubility in aqueous solvent. An organic acid prefers non-polar solvent when not dissociated (at low pH) and aqueous solvent when dissociated (at high pH).

Solubility of compounds is based on the universal law "Like dissolves like".

In your experiment, napthalene got contaminated with p-nitroaniline. This means that extraction efficiency was low. This can be improved by following methods:

1. Carry out multiple extractions instead of single extraction. For example, if you are using 500 mL HCl to extract p-nitroaniline, then use 100 mL of HCl at a time and carry out extraction five times.

Accurate calculations can be done using extraction efficiency formula.

2. Carry out continuous extraction using a Soxhlet extractor. It can separate mixtures well enough even when the analyte has unfavourable value of partition coefficient. Solvent is continuously passed until we get required amounts of compound.