Ethanol and Ethanoic Acid: Properties and Reactions for CBSE Class 10

Among the vast array of commercially manufactured carbon compounds, two compounds hold immense industrial, domestic, and laboratory significance: Ethanol (the primary alcohol) and Ethanoic Acid (commonly known as acetic acid). Ethanol is a versatile industrial solvent and medicine vehicle, while ethanoic acid is the active ingredient in kitchen vinegar and synthetic fabrics.

In CBSE Class 10 Science, Chapter 4 (Carbon and its Compounds) dedicates an entire section to their physical properties, physiological impacts, and four classic chemical reactions: Esterification, Saponification, Dehydration, and Carbonate Effervescence.

What You Will Learn

• Chemical formula, physical properties, and commercial uses of Ethanol
• Reactions of ethanol: reaction with sodium metal and dehydration with concentrated $\text{H}_2\text{SO}_4$
• Harmful biological effects of alcohol and denatured alcohol
• Chemical formula, physical properties, and Glacial Acetic Acid
• Reactions of ethanoic acid: Esterification and Saponification
• Reaction with carbonates and bicarbonates (the definitive diagnostic test)
• Step-by-step chemical test to distinguish between ethanol and ethanoic acid

1. Ethanol ($ext{CH}_3 ext{CH}_2 ext{OH}$)

Physical Properties:

• Formula: $\text{C}_2\text{H}_5\text{OH}$ or $\text{CH}_3-\text{CH}_2-\text{OH}$
• Appearance: Colourless liquid with a pleasant alcoholic odour and a burning taste.
• Boiling Point: $78^\circ\text{C}$ ($351\text{ K}$).
• Solubility: Highly soluble in water in all proportions due to hydrogen bonding.
• Nature: Neutral to litmus (does not change the colour of blue or red litmus paper).

Chemical Reactions of Ethanol:

1. Reaction with Sodium Metal (Hydrogen Evolution)

When a tiny piece of sodium metal is dropped into absolute ethanol, effervescence occurs as hydrogen gas is released: $2\text{CH}_3\text{CH}_2\text{OH} + 2\text{Na} \longrightarrow 2\text{CH}_3\text{CH}_2\text{ONa} \text{ [Sodium Ethoxide]} + \text{H}_2(g) \uparrow$ The evolved hydrogen gas burns with a pop sound. This reaction serves as a standard laboratory test for the alcohol group.

2. Dehydration Reaction (Formation of Ethene)

When ethanol is heated with excess concentrated sulphuric acid at strictly $443\text{ K}$ ($170^\circ\text{C}$), water is eliminated to produce unsaturated ethene gas:

$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow[443\text{ K}]{\text{Conc. } \text{H}_2\text{SO}_4} \text{CH}_2=\text{CH}_2 \text{ [Ethene]} + \text{H}_2\text{O}$

Important: <u>In this reaction, concentrated sulphuric acid acts as a powerful DEHYDRATING AGENT—a substance that removes water molecules from a compound.</u>

Biological Effects and Denatured Alcohol:

• Ingestion of ethanol depresses the central nervous system, impairs judgment, slows reflexes, and causes metabolic damage to the liver.
• Methanol Poisoning: Ingestion of even small quantities of methanol ($\text{CH}_3\text{OH}$) is fatal. Methanol is oxidized to methanal (formaldehyde) in the liver, which coagulates cellular protoplasm and attacks the optic nerve, causing permanent blindness and death.
• What is Denatured Alcohol? To prevent the misuse of cheap industrial alcohol for drinking, it is made poisonous by adding small amounts of methanol, pyridine, and blue copper sulphate dye. This foul-tasting, poisonous mixture is called denatured alcohol.

2. Ethanoic Acid ($ext{CH}_3 ext{COOH}$)

Physical Properties:

• Formula: $\text{CH}_3\text{COOH}$ (commonly called acetic acid).
• Appearance: Colourless liquid with a sharp, pungent vinegar smell and sour taste.
• Vinegar: A $5\% - 8\%$ solution of acetic acid in water is called vinegar, used widely as a food preservative in pickles.
• Glacial Acetic Acid: The melting point of pure ethanoic acid is $290\text{ K}$ ($17^\circ\text{C}$). In cold climates or during winter, pure ethanoic acid freezes into an ice-like crystalline solid, earning it the name glacial acetic acid.

Chemical Reactions of Ethanoic Acid:

1. Esterification Reaction (Formation of Sweet-Smelling Esters)

When ethanoic acid is heated with absolute ethanol in the presence of a few drops of concentrated sulphuric acid (catalyst), a fruity, sweet-smelling compound called an ester (ethyl ethanoate) is formed:

$\text{CH}_3\text{COOH} \text{ [Ethanoic acid]} + \text{CH}_3\text{CH}_2\text{OH} \text{ [Ethanol]} \xrightarrow{\quad \text{Acid Catalyst} \quad} \text{CH}_3\text{COOCH}_2\text{CH}_3 \text{ [Ethyl Ethanoate / Ester]} + \text{H}_2\text{O}$

• Esters are sweet-smelling substances used in making perfumes and artificial flavouring agents (e.g., in candies and ice creams).

2. Saponification Reaction (Alkaline Hydrolysis of Esters)

When an ester is treated with an alkali like sodium hydroxide, it hydrolyzes back into alcohol and the sodium salt of the carboxylic acid: $\text{CH}_3\text{COOCH}_2\text{CH}_3 + \text{NaOH} \longrightarrow \text{CH}_3\text{COONa} \text{ [Sodium Ethanoate]} + \text{CH}_3\text{CH}_2\text{OH} \text{ [Ethanol]}$ This reaction is called saponification because it is the exact chemical reaction used in the industrial manufacture of soaps from natural fats!

3. Reaction with Carbonates and Bicarbonates (The Diagnostic Test)

Ethanoic acid reacts with sodium carbonate and sodium hydrogen carbonate to produce brisk effervescence of carbon dioxide gas: $\text{CH}_3\text{COOH} + \text{NaHCO}_3 \longrightarrow \text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2(g) \uparrow$ $2\text{CH}_3\text{COOH} + \text{Na}_2\text{CO}_3 \longrightarrow 2\text{CH}_3\text{COONa} + \text{H}_2\text{O} + \text{CO}_2(g) \uparrow$ The liberated $\text{CO}_2$ gas turns lime water milky.

3. How to Distinguish Chemically Between Ethanol and Ethanoic Acid

In board exams, you will frequently encounter the question: "Give a chemical test to distinguish between ethanol and ethanoic acid."

4. Summary and Examination Tips

Exam Tip: Always state the Sodium Bicarbonate test when asked to distinguish between an alcohol and a carboxylic acid. It gives a clear, unmistakable visual indicator (brisk bubbling) that earns full marks immediately!

Common Mistake: Confusing esterification with saponification. Esterification is Acid + Alcohol $\to$ Ester + Water. Saponification is Ester + Base $\to$ Soap (Salt) + Alcohol!