An organic extraction is designed to separate benzoic acid (a weak monoprotic acid)
CHEMISTRY · Multi-part · CBSE · Chemistry · Aldehydes, Ketones and Carboxylic Acids · Aldehydes, Ketones and Carboxylic Acids
Problem
An organic extraction is designed to separate benzoic acid (a weak monoprotic acid), naphthalene (a nonpolar hydrocarbon), and aniline (a weak base) that are initially dissolved together in 100 mL of diethyl ether. The extraction scheme uses sequential washings with 1.0 M HCl(aq), 1.0 M NaOH(aq), and finally pure water before the organic layer is dried. The densities of the two bulk solvents are: diethyl ether ρ=0.71gmL−1, water ρ=1.00gmL−1.
(a) After the initial addition of 50 mL of 1.0 M HCl(aq) and vigorous mixing, identify which compounds (if any) move from the ether layer to the aqueous layer. Specify which layer (top or bottom) is organic at this stage and justify your answer.
(b) The aqueous layer from part (a) is removed. The remaining organic layer is now washed with 50 mL of 1.0 M NaOH(aq). Predict the new distribution of compounds between the two layers after this step and indicate the position (top or bottom) of each layer. Provide chemical equations where appropriate to support your reasoning.
(c) Explain why the final wash with pure water is necessary even after the target compound(s) are believed to be isolated in the ether layer. In your answer, address how miscibility, residual solutes, and density influence the cleanliness of the extracted product.
(d) Propose an experimental test (other than density measurement) that would allow a student to confirm which layer is the aqueous phase in any of the above washing steps. Justify how the test exploits differences in physical or chemical properties between the two phases.