In Part B of this experiment, the dichloromethane extract is washed repeatedly w

Question

In Part B of this experiment, the dichloromethane extract is washed repeatedly with water until the addition of AgNO3 to the water does not result in cloudiness or precipitate formation. (a) Why are these water washes necessary, i.e., what are they accomplishing? (b) What compound is causing the cloudiness/precipitation, i.e., what compound is precipitating from the aqueous solution? B. REACTION WORK-UP 1. Reread Lab Tips: Separatory Funnels. Transfer the reaction mixture to a 125 mL separatory funnel in the fume hood, slowly pouring to make sure the magnetic stir bar and boiling chips remain in the round bottom flask. Rinse the round bottom flask with 25 mL of dichloromethane [CAUTION: probable human carcinogen, wear gloves; flammable, no open flames] and add this rinse to the separatory funnel. 2. Mix the layers by inverting the separatory funnel and shaking gently [CAUTION: pressure build-up; vent periodically]. Ret the separatory funnel the ring stand, uncap it and allow the layers to separate. Transfer the dichloromethane layer (top or bottom layer) to a 125 mL Erlenmeyer flask. Cork the flask and keep it in the fume hood

Explanation / Answer

In the given procedure,

(a) water washed are necessary to remove halide from the system. The halide would interfere in the reaction and thus must be removed before by washing.

(b) the cloudiness comes from the formation of AgX (X is the halide) in the aqurous solution when AgNO3 is added to it.

AgNO3 + X- --> AgX + NO3-

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