OCHEM LAB QUIZZES

OCHEM LAB QUIZZES - Quiz#1 1 What are the 5 steps in the...

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Quiz #1 1. What are the 5 steps in the recrystallization of a compound? Find a suitable solvent for the recrystallization Dissolve the impure solid in a minimum volume of hot solvent Remove any insoluble impurities by hot filtration Slowly cool the hot solution to crystallize the desired compound from the solution Filter the solution to isolate the purified solid compound 2. What are the 4 important properties of a good solvent for recrystallization? The compound should be very soluble at the boiling point of the solvent and only sparingly soluble in the solvent at room temperature. The unwanted impurities should be either very soluble in the solvent at room temperature or insoluble in the hot solvent. The solvent should not react with the compound being purified. The solvent should be volatile enough to be easily removed from the solution after the compound has crystallized. 3. What effects do impurities have on the melting point of mixtures? Impurities in the sample lower or depress the melting temperature and broaden the melting range. 4. What is the purpose of a mixed melting point? Helps in the determination of an unknown solid. The mixture will have an unknown solid mixed with a known pure compound. If the two compounds are identical, there will be no effect on the melting point. 5. What are the ways of inducing crystallization? Scratching the inner wall of the flask with a glass stirring rod.
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