Determination of Melting Points of Benzoic Acid and Benzamide and Composition Diagram of Their Mixtures PURPOSE: The purpose of this experiment is to determine the melting point of benzoic acid and benzamide and make a composition diagram for the mixtures of benzoic acid and benzamide to determine the eutectic point of the mixtures. The melting point of the given unknown will be determined using the melting point apparatus. Pure chemicals such as benzoic acid and benzamide alone have a set melting point, but when missed with impurities or each other, the melting point decreases depending on What is the effect of an insoluble impurity, such as charcoal, on the observed melting point? 2. One of the most common causes of an inaccurate melting point is too rapid heating of the melting point apparatus. Under these circumstances, how will the observed melting point compare with the true melting point? Solubility In this experiment you will determine the solu bilities of phthalic acid, sucrose and acetanilide in four different solvent: water, ethyl alcohol, acetone and petroleum ether. You will need to select the best solvent for recrystallization of the above compounds.
1. To determine solubility, place 0. 02 g (20 mg) of a powdered compound in a test tube and add 0. 5 ml of a solvent. Stir with a spatula and note whether the compound dissolves or not. Record your data in the columns labeled RT (for room temperature).
Use (+) when your compound is soluble, (-) if is not soluble and if it is partially soluble. 2. If the boiling point of a solvent is less than 100^0 C, place the test tube in a boiling water bath (use a test tube holder). (If the boiling point is greater or equal to 100^0 C, the test tube may be heated directly on a hot plate. ) Stir and see whether your compound dissolves. Take care to make your observations before the solvent evaporates.
Record your data in the columns labeled HOT. 3. If the compound dissolves, place the test tube in ice bath to determine if the compound will precipitate upon cooling. If it precipitates out, enter yes on your lab report, otherwise enter no. The best solvent for recrystallization will have the following properties: .
The compound will not completely dissolve in the solvent at room temperature... The compound completely dissolves in the solvent at its boiling point... Upon cooling, the compound will precipitate.