Frank Brothers Solutions for ICSE Class 10 Chemistry Chapter 11e Alcohols

Alcohols

Solution 1:
Answer: Molecular formula of Ethanol: \( C_2H_5OH \)
Structural formula of Ethanol:
H H
H-C-C-O-H
H H
In simple words: Ethanol is made of 2 carbon atoms, 6 hydrogen atoms, and 1 oxygen atom joined together in a specific pattern with an -OH group attached.

📝 Teacher's Note: Show students how to count atoms in the structural formula and relate it to the molecular formula. Emphasize the -OH functional group that makes it an alcohol.

🎯 Exam Tip: Always draw the structural formula clearly showing all bonds, especially the C-O-H arrangement for the alcohol group.

Solution 2:
Answer: Necessary conditions and equations of getting ethanol from the following are:
(a) Alkyl halide: alkyl halide on hydrolysis with dilute alkali give alcohol
\( C_2H_5Br + KOH(aq) \rightarrow C_2H_5OH + KBr \)
(b) An ethene: Ethene is first treated with concentrated sulphuric acid at 80°C when ethyl hydrogen sulphate is formed. Ethyl hydrogen sulphate on hydrolysis with boiling water or steam yield ethanol.
\( CH_2 = CH_2 + H_2SO_4 \xrightarrow{80°C} CH_3CH_2HSO_4 \)
\( CH_3CH_2HSO_4 + H_2O \xrightarrow{boiling} CH_3CH_2OH + H_2SO_4 \)
In simple words: We can make ethanol from bromoethane by treating it with alkali, or from ethene by first adding sulfuric acid and then adding water.

📝 Teacher's Note: Demonstrate both methods with molecular models to show how the -OH group replaces -Br in method (a) and gets added across the double bond in method (b).

🎯 Exam Tip: Remember the two-step process for ethene to ethanol conversion and write both equations with proper conditions and temperatures.

Solution 3:
Answer: (i) Potassium dichromate and potassium permanganate in the presence of acid
(ii) Conc.\( H_2SO_4 \)
(iii) Methanol
(iv) Ethyl alcohol
In simple words: These are different chemicals and compounds related to alcohol chemistry - some are oxidizing agents that can change alcohols, and others are types of alcohols themselves.

📝 Teacher's Note: Explain the role of each compound - oxidizing agents convert alcohols to aldehydes/acids, while concentrated acid acts as a dehydrating agent.

🎯 Exam Tip: Learn which reagents are oxidizing agents and which are dehydrating agents for alcohol reactions.

Solution 4:
Answer: Ethanol reacts as follows:
(a) Metallic sodium:
\( 2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2 \)
(b) Acetic acid:
\( C_2H_5OH + CH_3COOH \xrightarrow{conc H_2SO_4} CH_3COOC_2H_5 + H_2O \)
(c) Conc.\( H_2SO_4 \):
\( C_2H_5OH \xrightarrow{conc H_2SO_4, 170°C} CH_2 = CH_2 + H_2O \)
In simple words: Ethanol can react with sodium metal to release hydrogen gas, with acetic acid to form an ester, and with concentrated sulfuric acid to form ethene by losing water.

📝 Teacher's Note: Demonstrate the sodium reaction carefully as it produces flammable hydrogen gas. Explain esterification and dehydration as two important alcohol reactions.

🎯 Exam Tip: Remember the specific conditions for each reaction - temperature for dehydration (170°C) and catalyst for esterification (conc H₂SO₄).

Solution 5:
Answer: (i) Methylated spirit: Ethyl alcohol mixed with certain percentage of methyl alcohol
(ii) Power alcohol: Petrol:Alcohol in 4:1
(iii) Spurious alcohol: Ethyl alcohol mixed with higher percentage of methyl alcohol
In simple words: These are different mixtures of alcohols - methylated spirit has some methyl alcohol added to ethyl alcohol, power alcohol mixes alcohol with petrol for fuel, and spurious alcohol has too much methyl alcohol which makes it dangerous.

📝 Teacher's Note: Emphasize the safety aspect - spurious alcohol is dangerous because methyl alcohol is toxic. Explain why methylated spirit is made (to prevent drinking).

🎯 Exam Tip: Remember the ratios and compositions - power alcohol is 4:1 petrol to alcohol, and spurious alcohol has high methyl alcohol content.

Solution 6:
Answer: Uses of ethanol:
(i) In the manufacture of alcoholic beverages
(ii) As a solvent for paint, oils, perfumes
(iii) As an antifreeze in automobile radiators
In simple words: Ethanol is used to make alcoholic drinks, as a liquid that can dissolve other substances like paint and perfumes, and to prevent water from freezing in car engines.

📝 Teacher's Note: Connect these uses to ethanol's properties - its ability to dissolve substances, its low freezing point, and its consumable nature when pure.

🎯 Exam Tip: List at least three diverse uses showing industrial, commercial, and automotive applications of ethanol.

Solution 7:
Answer: (i) Ethanol to ethene:
\( C_2H_5OH \xrightarrow{conc H_2SO_4, 170°C} CH_2 = CH_2 + H_2O \)
(ii) Bromoethane to ethanol:
\( C_2H_5Br + KOH(aq) \rightarrow C_2H_5OH + KBr \)
In simple words: We can convert ethanol to ethene by heating it with concentrated sulfuric acid to remove water, and we can convert bromoethane to ethanol by treating it with potassium hydroxide.

📝 Teacher's Note: Show that these are reverse processes - dehydration removes water while nucleophilic substitution replaces halogen with -OH group.

🎯 Exam Tip: Include the specific temperature (170°C) for dehydration and specify aqueous KOH for the substitution reaction.

Solution 8:
Answer: \( C_2H_5OH \xrightarrow{[O]} CH_3CHO \xrightarrow{[O]} CH_3COOH \)
(X) (Y)
\( CH_3COOH + C_2H_5OH \xrightarrow{conc H_2SO_4} CH_3COOC_2H_5 \)
(Y) (X) (Z)
'X' = Ethyl alcohol
'Y' = Ethanoic acid
'Z' = Ethyl ethanoate
In simple words: This shows how ethanol (X) gets oxidized step by step to form acetaldehyde and then acetic acid (Y), which then reacts back with ethanol to form ethyl acetate (Z).

📝 Teacher's Note: Explain the oxidation sequence and then the esterification reaction. Show how the same compound (ethanol) appears as both reactant and product in different steps.

🎯 Exam Tip: Clearly identify each compound with its correct chemical name and show the [O] symbol for oxidation reactions.