The primary reason for the addition of anhydrous calcium chloride to the organic

Question

The primary reason for the addition of anhydrous calcium chloride to the organic solvent layer resulting from the extraction of an organic compound from water is to a) remove residual water b) remote residual NaCl c) remove residual acid catalyst d) neutralize the residual NaOH Ten grams of an organic solid is dissolved in 100 ml of H_2 O (solvent 1). Which of the following extraction methods will remove the largest amount of the organic solid from the aqueous solution? a) three 50 ml portion extractions with ether (solvent 2) b) two 50 ml portion extractions with ether (solvent 2) c) one 150 ml portion extraction with ether (solvent 2) d) one 50 ml portion extraction with ether (solvent 2) Two organic solid compounds, A and B are observed to have the same melting point. What should be done to prove that these substances are the same compound? a) look up the literature m.p. values of compound A and B b) recrystallize compound A c) recrystallize compound B d) perform a mixed melting point on a sample containing equal amounts of compounds A and A key step in the recrystallization process is a) dissolve the solid in a large quantity of cold solvent b) remove all of the soluble impurities by vacuum filtration c) allow the hot solution to cool slowly and precipitate the solid d) take a melting point of the wet crystals e) all of the above

Explanation / Answer

1. the primary reason to add anhydrous calcium chloride in organic solvent layer resulting from the extraction of organic compount from water is to remove residual water. calcium chloride acts as a drying agent for the organic layer to remove any remaining aqueous solvent.

2. 10 g of organic solid is dissolved in 100 mL water. The extraction method which will remove the largest amount of solid from water is multiple extraction. two 50 mL extraction with ether will be more efficient. Total solvent 100 mL is divided into small portion of 50 mL.

3. 2 organic compounds are having the same melting point. To prove that substance are of same compound. The identity of two samples that have the same melting point can be determined by taking a mixed melting point. Grind roughly equal portions of the two samples together to mix well and take a melting point of the mixture. If the two substances are identical the melting point should be the same as that of either sample. If the two substances are not identical, then the melting point will be depressed.

4. Key step to recrystallization process is to dissolve the impure substance in hot water. Allow it to cool down slowly. The impure substance will crystallize in its pure form and the imputities will be left in solution which will be filtered later.

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