Ester is a class of organic compounds formed by the reaction of a carboxylic acid, acyl chloride or acid anhydride with alcohol. In it, the hydroxy (-OH) group of the carboxylic acid, acyl chloride or acid anhydride is replaced by the alkoxy (-OR) group of the alcohol. They have a fruity smell and are relatively soluble in water.
| Definition: Ester is a sweet-smelling chemical compound derived from the reaction of a carboxylic acid, acyl chloride or acid anhydride with alcohol. |
Ester Chemistry Questions with Solutions
Q1. Which of the following acts as a catalyst for the esterification of alcohol and carboxylic acid?
(a) Nitrous acid
(b) Nitric acid
(c ) Sulphuric acid
d) None of the above
Answer: (c ) Sulphuric acid acts as a catalyst for the esterification of alcohol and carboxylic acid.
Q2. Hydrolysis of ester leads to the formation of which of the following products in an acidic medium?
(a) Alcohol and carboxylic acid
(b) Alcohol and sodium carboxylate
(c ) Alcohol and ether
(d) None of the above
Answer: (a) Hydrolysis of ester leads to the formation of alcohol and carboxylic acid in an acidic medium.
Q3. What is the characteristic odour of an ester?
(a) Alcoholic odour
(b) Fruity like odour
(c) Rotten egg odour
(d) None of the above
Answer: (b) Ester has a characteristic odour of fruits.
Q4. Hydrolysis of ester leads to the formation of which of the following products in an alkaline medium?
(a) Alcohol and carboxylic acid
(b) Alcohol and sodium carboxylate
(c ) Alcohol and ether
(d) None of the above
Answer: (b) Hydrolysis of ester leads to the formation of alcohol and sodium carboxylate in an alkaline medium.
Q5. Alkaline hydrolysis of the ester is commonly known as
(a) Neutralisation reaction
(b) Saponification reaction
(c ) Hydrolysis reaction
(d) None of the above
Answer: (b) Alkaline hydrolysis of the ester is commonly known as saponification reaction.
Q6. What is an ester?
Answer: Ester is a class of organic compounds formed by the reaction of a carboxylic acid, acyl chloride or acid anhydride with alcohol. In it, the hydroxy (-OH) group of the carboxylic acid, acyl chloride or acid anhydride is replaced by the alkoxy (-OR) group of the alcohol.
Q7. What is the general formula of an ester?
Answer: Esters have a general formula of RCOOR’.
Q8. What is an esterification reaction?
Answer: An esterification is a reaction between a carboxylic acid and an alcohol. It is used to synthesise ester. The reaction proceeds in the presence of dilute sulphuric acid.
RCOOH + R′OH ⇌ RCOOR′ + H2O
Q9. What is ester hydrolysis?
Answer: The addition of water to an ester to yield alcohol and carboxylic acid or carboxylate salt in an acid or a base is known as ester hydrolysis. It is also known as a desertification reaction.
Q10. Is ester soluble in water?
Answer: Ester is relatively soluble in water. Ester consists of an oxygen atom which forms hydrogen bonding with water making it slightly soluble in water. However, esters of high molar mass are insoluble in water.
Q11. What is the ammonolysis of an ester?
Answer: The reaction of an ester with ammonia to yield the corresponding amide is known as the ammonolysis of an ester.
CH3COOC2H5 + NH3 → CH3CONH2 + C2H5OH
Q12. How can we synthesise an ester?
Answer: We can synthesise ester by reacting acyl chlorides or acid anhydrides with alcohol.
RCOCl + R′OH → RCOOR′ + HCl
Q13. What is a transesterification reaction?
Answer: The reaction of an ester with alcohol to change one ester into another one in the presence of an acid or a base is known as a transesterification reaction.
RCOOR′ + CH3OH → RCOOCH3 + R′OH
Q14. Distinguish between an ester and an ether.
Answer:
| S. No. | Ester | Ether |
|---|---|---|
| 1. | Ester is a sweet-smelling chemical compound derived from the reaction of a carboxylic acid with an alcohol. | Ether is a chemical compound derived from the dehydration of alcohols. |
| 2. | It has a general formula of RCOOR’. | It has a general formula of ROR’. |
| 3. | They are unsymmetrical due to the presence of a carbonyl group. | They are symmetrical. |
| 4. | Example: Methyl butanoate | Example: Diethyl ether |
Q15. Match the following.
| Column I | Column II |
|---|---|
| Ester | R(CO)R |
| Aldehyde | RCOOR’ |
| Ketone | RCHO |
| Carboxylic Acid | ROH |
| Alcohol | RCOOH |
Answer:
| Column I | Column II |
|---|---|
| Ester | RCOOR’ |
| Aldehyde | RCHO |
| Ketone | R(CO)R |
| Carboxylic Acid | RCOOH |
| Alcohol | ROH |
Practise Questions on Ester
Q1. What is reverse esterification?
Q2. What is saponification reaction?
Q3. What are the applications of an ester?
Q4. What is an acid catalysed ester hydrolysis?
Q5. Explain the mechanism of base catalysed ester hydrolysis?
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