A Mixture Of Three Substances ( Benzoic Acid Essay

A Mixture Of Three Substances ( Benzoic Acid Essay

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In this experiment, a mixture of three substances (benzoic acid, 2-naphthol, and 1-4 dimethoxybenzene) will be separated based off acidity strength using the liquid-liquid extraction technique through a separatory funnel. Benzoic acid and 2-napthol will be converted into ionic salts when reacting with their appropriate bases (sodium bicarbonate and sodium hydroxide). Both ionic salts will then form solids through the addition of acidic HCl. Neutral 1,4 – dimethoxybenzene forms a solid through the evaporation of ether. Each compound will then be purified through recrystallization, using the processes of dissolving the solid in either water or methanol, and isolating the solid through vacuum filtration. After a week of evaporation, the compounds will then be examined for both identification purposes and purity based on melting point analysis and IR spectrum.
1. Compound 1 was identified to be Benzoic Acid. The sample’s melting point range (122.5°C -123.2°C) fell within the range of pure Benzoic Acid (121°C – 125°C). The IR spectra also provided key peaks only found in Benzoic Acid compared to the other compounds, such as the carboxylic C=O stretch at 1678.44 cm-1 and the very broad O-H stretch at 2552.89 cm-1 – 3071.13 cm-1. Based on the acid/base chemistry, the reaction between sodium bicarbonate and benzoic acid leads to the products of the sodium salt of benzoic acid and carbonic acid. Compound 2 was identified to be 2-naphthol. The sample’s melting point range (121.3°C – 122.6°C) was slightly below the range of pure 2-naphthol (123°C – 124°C), therefore melting point analysis was not sufficient to determine the identity of the compound. The IR spectra on the other hand provided many key peaks such as a much more narrow...


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...and conversion to an ionic salt. Compound 2 (2-naphthol) would then be extracted with sodium hydroxide.


Based off the reaction, the conjugate acid (pKa = 15.7) is weaker than the starting acid (pKa=14.7), resulting in the formation of products and conversion to an ionic salt. Using the base of sodium hydroxide first results in a failure of separation. Because the conjugate acid of sodium hydroxide is a weaker acid than both the starting acids Benzoic acid and 2-naphthol, both compounds would be extracted together from the mixture. The conjugate acid of sodium bicarbonate on the other hand is a stronger acid than 2-naphthol, therefore products would never form due to equilibrium lying towards the reactants. Sodium bicarbonate assures compound 1 and 2 would be separated from one another due to the strength of acidity, represented by the following reaction.

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