Question

Benzamide can be prepared by the action of concentrated ammonia upon benzoyl chloride.
$\underset{Benzoyl\text{ }Chloride}{\mathop{{{C}_{6}}{{H}_{3}}COCl}}\,+2N{{H}_{3}}\to \underset{Benzamide}{\mathop{{{C}_{6}}{{H}_{5}}CON{{H}_{2}}}}\,+N{{H}_{4}}Cl$
- In one such experiment, 65 cc of concentrated ammonia (in excess) was reacted with 15 g of benzoyl chloride to give 11.1g of pure benzamide. Molar masses: benzoyl chloride (141); benzamide (121). The percentage yield of benzamide is:
[A] $\dfrac { 11.1 }{ 15 } { \times 100 }$
[B] $\dfrac { \left( 15-11.1 \right) }{ 15 } { \times 100 }$
[C] $\dfrac { 11.1 }{ 65 } { \times 100 }$
[D] $\dfrac { 121 }{ 141 } { \times 100 }$
[E] $\dfrac { 11.1\times 141 }{ 121\times 15 } { \times 100 }$

Answer 1

To solve this question, firstly find out the amount of benzamide in 15 g of benzoyl chloride. Then you can find out the percentage yield from the calculated amount and given amount. You can use the formula - $Percentage\text{ }yield\text{ }=\dfrac{Actual\quad amount\quad of\quad product}{Calculated\quad amount\quad of\quad product}\times 100$

Complete Solution :
In the question, we can see that the calculated amount of benzamide is given to us. We have to find out the percentage yield from the given experiment. So for that, firstly let us calculate the amount of benzamide in 15g of benzoyl chloride.
- The molar mass of benzamide is given to us as ${ { 121gmol }^{ -1 } }$
And the molar mass of benzoyl chloride is given as ${ { 141gmol }^{ -1 } }$
Amount of benzamide formed from 1g of benzoyl chloride = $\dfrac{121}{141}$
Therefore, amount of benzamide formed from 1g of benzoyl chloride = $\dfrac{121}{141}\times 15$

But, the actual amount of benzamide formed is given to us as ${ 11.1g }$
- We know that, Percentage yield = $\dfrac { Actual\quad amount\quad of\quad product }{ Calculated\quad amount\quad of\quad product } { \times 100 }$
Therefore, putting the values in the above relation we can write that-
- Percentage yield = $\dfrac { 11.1\times 100 }{ \left( \dfrac { 121 }{ 141 } { \times 15 } \right) }$
Percentage yield = $\dfrac { 11.1\times 141 }{ 121\times 15 } { \times 100 }$
- Therefore, we can see that the correct answer is . $\dfrac { 11.1\times 141 }{ 121\times 15 } { \times 100 }$
So, the correct answer is “Option E”.

Note: Benzamide is the simplest amide derivative of benzoic acid and it is a white crystalline solid. We can describe the uses of benzamide as-
-It possesses many pharmacological activities such as analgesic, antimicrobial, anticancer, anti-inflammatory, cardiovascular, and many other biological activities.
- Its chromophore is widely used as a cotton-gin derivative of primary amines.
- It acts as a pain-relieving (otherwise called a painkiller)
- It is an antimicrobial agent. It is an agent that can act against the microorganism by inhibiting its growth or killing them.