Question

In: Chemistry

1. The glassware that is to be used for a Grignard reaction is washed with water...

1. The glassware that is to be used for a Grignard reaction is washed with water and acetone, and dried thoroughly before the reaction is to be performed. Select the most likely reason why.

   a. Acetone is needed to react with the silanol groups on the surface of the glassware.

   b. The acetone adheres to the sides of the glassware as it dries, and it catalyzes the formation of the Grignard reagent.

c. Grignard reactions are highly endothermic, and residual water will freeze during the reaction.

d. If the glassware is not completely dry, residual water or acetone will react with the Grignard reagent.

2. A Grignard reaction is to be performed in diethyl ether solvent. Select the appropriate grade of diethyl ether for a Grignard reaction.

a. anhydrous grade

b. spectroscopy grade

c. ACS grade

d. technial grade

3. Crude triphenylmethanol was recrystallized using a 2:1 mixture of hexane:ethanol. Select the most likely reason why this recrystallization solution was chosen over pure ethanol.

a. Formation of triphenylmethanol crystals in the presence of pure ethanol is rapid, resulting in lower purity.

b. Triphenylmethanol is very soluble in pure ethanol and its recovery during recrystallization would be low.

c. Hexane stabilizes the phenyl groups of triphenylmethanol, protecting it from decomposition in the presence of heat.

d. Triphenylmethanol is relatively insoluble in pure ethanol, and not enough of it would dissolve for a recrystallization.

4. Which of the following is NOT a reason why heating a reaction mixture directly on the surface of a hot plate can be problematic?

a. Hot plates can heat glassware unevenly, which can lead to stress and cracking.

b. It is difficult to measure and maintain the temperature of a reaction when using the common, traditional style of hot plate.

c. Flammable solvents with low boiling points may ignite.

d. Hot plates cannot heat above 200 °C.

5. A Grignard reaction is performed by heating phenylmagnesium bromide and benzophenone under reflux in diethyl ether. Given that diethyl ether boils at 35 °C and benzophenone boils at 305 °C, select the appropriate temperature for the reflux.

a. 35 C

b. 25 C

c. 305 C

d. 100 C

Solutions

Expert Solution

1. The glassware that is to be used for a Grignard reaction is washed with water and acetone, and dried thoroughly before the reaction is to be performed. The most likely reason for this procedure is,

d. If the glassware is not completely dry, residual water or acetone will react with the Grignard reagent.

2. A Grignard reaction is to be performed in diethyl ether solvent. The appropriate grade of diethyl ether for a Grignard reaction would be,

a. anhydrous grade

3. Crude triphenylmethanol was recrystallized using a 2:1 mixture of hexane:ethanol. The most likely reason why this recrystallization solution was chosen over pure ethanol is,

b. Triphenylmethanol is very soluble in pure ethanol and its recovery during recrystallization would be low.

4. Of the following the one which is NOT a reason why heating a reaction mixture directly on the surface of a hot plate can be problematic is,

d. Hot plates cannot heat above 200 °C.

5. A Grignard reaction is performed by heating phenylmagnesium bromide and benzophenone under reflux in diethyl ether. Given that diethyl ether boils at 35 °C and benzophenone boils at 305 °C, The appropriate temperature for the reflux would be,

a. 35 C


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