Question

6. During the synthesis of a Grignard reagent in diethyl ether solvent, bubbles are observed on the surface of the magnesium. Select the correct identity of the bubbles.

a. The bubbles are gaseous O2.

b. The bubbles are gaseous H2.

c. The bubbles are gaseous diethyl ether.

d. The bubbles are gaseous magnesium byproducts.

7. Prior to the synthesis of a Grignard reagent, the magnesium that is used in the reaction must be activated. Select the action that best describes this activation step.

a. exposing the magnesium to UV light to promote its electrons to an excited state

b. increasing the temperature to 150 °C to oxidize the surface layer of magnesium

c. soaking the magnesium in water to clean the surface layer

d. scraping or crushing the magnesium to expose fresh, unoxidized surface

8. A synthesis procedure calls for the trituration of the crude product prior to recrystallization. Select the most likely consequence of failing to triturate the crude reaction product.

a. Less of the crude product will recrystallize from the recrystallization solvent.

b. Less of the crude product will dissolve into the recrystallization solvent.

c. The recrystallized product will contain less impurities than it would if it had not been triturated.

d. The mass of the recrystallized product will be lower than it would have been if it were triturated.

9. Select the term that describes the act of grinding a solid with a stirring rod or spatula in the presence of a solvent.

a. salting out

b. centrifugation

c. sonication

d. trituration

10. Select the action that will NOT help increase the yield of a Grignard reagent.

a. dry the glassware in an oven prior to use

b. use only anhydrous ether as solvents

c. scrape or grind the Mg pieces prior to use

d. rinse the reaction glassware with acetone immediatelt prior to use

11. A reaction product mixture containing hydrocarbons in diethyl ether is washed with saturated aqueous sodium chloride (brine) solution in a separatory funnel. Select the most likely reason for this step.

a. This step is to extract sodium chloride into the ether layer.

b. This step is to remove water from the ether layer.

c. This step is to extract the ether into the aqueous layer.

d. This step is to extract the hydrocarbons into the aqueous layer.

Answer 1

6) Grignard reagent is synthesized by reacting Magnesium with alkyl/aryl halide in diethyl ether solvent. There is not hydrogen or oxygen evolution in this reaction.

So the only reason that bubbles are formed is because of local heating due to the fact that the reaction is exothermic so.

c. The bubbles are gaseous diethyl ether.

7) The activation of magnesium for the grignard reaction is critical This is generally accomplished by removing the oxidised magnesium surface. So the right answer is

d. scraping or crushing the magnesium to expose fresh, unoxidized surface.

8) trituration of the crude product ensures removal of some of the high amount of impurity from the adhered pure product so if this step is not carried out the outcome should be. Recrystllization is a phenomenon which is promoted by having more pure material in the crude mixture.

a. Less of the crude product will recrystallize from the recrystallization solvent.

9)the term that describes the act of grinding a solid with a stirring rod or spatula in the presence of a solvent.

d. trituration - this act ensure that the material gets washed well to aid in further purification preferably by crystallization.