Answer: It is preferable to add excess bromobenzene instead of excess acetophenone because the reaction is exothermic and the addition of too much acetophenone causes the temperature to rise rapidly which may lead to an explosion.
Explanation:
The preparation of 1,1- diphenyl ethanol by reaction between bromobenzene and acetophenone is known as Grignard reaction.
The mechanism of this reaction is given in the adjoining image.
In this reaction, acetophenone is added slowly and in small amounts because this reaction is exothermic.
If a large quantity of acetophenone is added simultaneously, it can lead to the temperature rising too much in a short duration of time and may cause an explosion which may injure the person performing this reaction.
Also, too much acetophenone becomes an impurity which further hampers the reaction.
Therefore, it is preferable to add excess bromobenzene instead of excess acetophenone.
To know more about "Grignard Reaction", refer to the following link:
brainly.com/question/17135014?referrer=searchResults
#SPJ4