notes_162_Exp_4_Notes_041608

notes_162_Exp_4_Notes_041608 - EXPERIMENT 4 EFFECT OF...

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EXPERIMENT 4: EFFECT OF TEMPERATURE ON SOLUBILITY AND FRACTIONAL CRYSTALLIZATION I. Fractional Crystallization of KNO 3 with (NH 4 ) 2 Fe(SO 4 ) 2 . 6H 2 O Impurity II. Determining the Solubility Curve of KNO 3
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In this experiment, you will examine crystallization and recrystallization as a purification technique. Æ Crystallization and recrystallization are used extensively for the isolation and purification of organic and inorganic compounds. Æ The technique exploits the differences in solubility of the components in a mixture. The desired compound is crystallized while impurities remain in solution. Note: Time management will be critical with this lab, so be sure to follow the lab manual and your TA’s instructions regarding multi- tasking so that you can finish the experiment.
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Fig 17.5, pg 838 in Zumdahl Fe(NH 4 ) 2 (SO 4 ) 2 .6H 2 O will have a similar trend to the KCl line shown here.
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Problem Consider the problem of separating a mixture consisting of 200 grams of KNO 3 (target compound) and 10 grams of (NH 4 ) 2 Fe(SO 4 ) 2 .6H 2 O (impurity). Approach Cooling from 95ºC to 0ºC… Æ 10 g KNO 3 (aq) remain in solution at 0ºC because of the solubility of KNO 3 (see Fig 17.5 on the previous slide or Figure 1 on pg 46 of the lab manual) Æ 190 g KNO 3 (s) crystallize Æ 10 g of (NH 4 ) 2 Fe(SO 4 ) 2 · 6H 2 O (aq) remain in solution Æ Filter and dry the nearly pure KNO 3 a small amount of (NH 4 ) 2 Fe(SO 4 ) 2 .6H 2 O (aq) may get trapped in the KNO 3 crystals, but only a small amount considerably less than the 10 g original amount
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