Question

lab report for separation and purification of benzoic acid, benzoin, 1,4-dibromobenzene

Answer 1

The first thing you need to know here is the main functional group of every compound presented here. The benzoic acid is an carboxilic acid, benzoin is a ketone and 1.4-dibromobenzene is a neutral compound. So yu have a mixture of an acid and two neutral compound.

Next, you need to know the polarity of these compounds. Why do you need that? because in order to do a separation scheme, you will need to find a solvent in which the three compounds are soluble and can be mixed. Use your text book to know the properties of these 3 compounds. The benzoic acid is slightly polar because of the presence of the OH group, but benzoin and dibromobenzene are non polar.

So, what can you do here? you may use a non polar solvent (Like acetone or hexane) so you may dissolve benzoin and dibromobenzene, and then, filter the acid, or you may use a polar solvent like methanol to disolve the acid and benzoin and then, separate the dibromobenzene. You may also use a medium polar solvent like diclore methane, so the three compounds are dissolved, and then, you may do the identification of your 3 compounds.

In the next picture, you have a separation scheme and part of purification:

Now, once you have separated the three compounds, you need to purify. How are you going to do that? well, you need to find a solvent in which the compounds are not soluble at room temperature, but they do at high temperature. Once you find that solvent, just dissolve your compounds into the differents solvents you find in high temperature. let it cool at room temperature or use an ice bath, and let the crystals comes out. Then, filter the crystals, measure the melting point and if possible, use a NMR spectrum.

If you have doubts, or something, you may tell me. Hope this helps.