10th Class Chemistry Notes 2026 — Chapter 23
Class 10 Chemistry — Chapter 23: Monohydroxy Alkanes or Alcohols
Quran Education Point
Board: Punjab Board
A. Multiple Choice Questions (MCQs)
23.1 Which conditions are best for the fermentation of glucose?
(a) 35°C, fresh yeast, absence of oxygen
(b) 45°C, yeast
(c) 45°C, absence of oxygen
(d) 35°C, fresh yeast
Correct Answer: (a) 35°C, fresh yeast, absence of oxygen
23.2 Which catalyst other than H₃PO₄ can also be used for the hydration of alkenes?
(a) NaOH
(b) H₂SO₄
(c) CH₃COOH
(d) Ni
Correct Answer: (b) H₂SO₄
23.3 Which alcohol has the maximum heat of combustion?
(a) CH₃CH₂CH₂OH
(b) CH₃CH₂OH
(c) CH₃OH
(d) CH₃CH₂CH₂CH₂OH
Correct Answer: (d) CH₃CH₂CH₂CH₂OH
23.4 Which is the most environmentally friendly fuel among the following?
(a) Coal
(b) Kerosene oil
(c) Ethanol
(d) Wood
Correct Answer: (c) Ethanol
23.5 Which property or properties of ethanol make it suitable for the cosmetic industry?
(a) Easily flammable
(b) Highly volatile and deodorizing
(c) Antipyretic
(d) Sedative
Correct Answer: (b) Highly volatile and deodorizing
23.6 What is the correct name of the following alcohol?
CH₃−CH(OH)−CH₂−CH(CH₃)−CH₃
(a) 2-Methylpentan-4-ol
(b) 4-Methylpentan-2-ol
(c) Hexan-2-ol
(d) Hexan-4-ol
Correct Answer: (b) 4-Methylpentan-2-ol
23.7 Which property of ethanol makes it suitable for cleaning wounds?
(a) Good solvent
(b) Volatility
(c) Antiseptic
(d) Deodorizing
Correct Answer: (c) Antiseptic
23.8 Which alcohol is added to petrol to improve combustion and is also used as a raw material for preparing vinegar and many other organic compounds?
(a) Propanol
(b) Propan-2-ol
(c) Ethanol
(d) Methanol
Correct Answer: (c) Ethanol
B. Short Answer Questions
23.1 Give two advantages of burning alcohols over burning fossil fuels.
1. Cleaner combustion: Alcohols generally burn with less soot and can produce fewer sulphur-containing pollutants than many conventional fossil fuels.
2. Renewable source: Alcohols such as ethanol can be produced from renewable biomass. The plants used to produce biomass absorb carbon dioxide during growth, although the overall environmental impact depends on production and processing methods.
23.2 Which properties of ethyl alcohol make it useful in the cosmetic industry?
Ethyl alcohol is useful in the cosmetic industry because of its high volatility and deodorizing properties. It evaporates quickly without leaving an oily residue and acts as a solvent and carrier for fragrances in perfumes, body sprays, and other cosmetic products.
23.3 How is ethyl alcohol important to the pharmaceutical industry?
Ethyl alcohol is an effective solvent for many medicinal substances that are poorly soluble in water. It is used in the preparation of tinctures, certain cough syrups, liquid medicines, antiseptic solutions, and disinfectants.
23.4 Give any two disadvantages of fermentation reactions.
Slow process: Fermentation takes several days to complete under suitable conditions.
Impure product: Fermentation produces a dilute alcoholic solution containing water and other impurities. Further purification, usually by distillation, is required.
23.5 Write down the conditions involved in the hydration of ethene.
The conditions for the hydration of ethene are:
Catalyst: Phosphoric acid (H₃PO₄).
Temperature: Approximately 300°C.
Pressure: Approximately 60 atmospheres.
Ethene reacts with steam to produce ethanol.
C. Constructed Response Questions
23.1 How is ethanol obtained as a by-product in the sugar industry?
During sugar production, a thick liquid called molasses remains after sugar crystallization. Molasses contains fermentable sugars.
The molasses is diluted with water, and yeast is added. Under suitable conditions, generally around 30–35°C in the absence of oxygen, yeast enzymes convert the sugars into ethanol and carbon dioxide.
The process converts a by-product of the sugar industry into a useful product.
23.2 Why do we obtain relatively impure alcohol through fermentation?
Fermentation produces a mixture containing ethanol, water, yeast cells, unreacted sugars, and other by-products. These substances remain mixed with the alcohol after fermentation.
Furthermore, yeast activity becomes limited when the alcohol concentration rises significantly. Therefore, the fermented mixture must be purified, commonly through distillation, to obtain concentrated ethanol.
23.3 How do the properties of ethyl alcohol make it useful as a fuel?
1. Heat of combustion: Ethanol releases heat when it burns in oxygen, making it useful as a fuel.
2. Mixing with petrol: Ethanol can be blended with petrol. Its relatively high octane rating helps reduce engine knocking in suitable engines and fuel blends.
3. Renewable production: Ethanol can be produced from biomass, providing an alternative to fuels obtained entirely from fossil resources.
D. Descriptive Questions
23.1 Compare fermentation and catalytic hydration of ethene for the preparation of ethanol.
Feature | Fermentation | Catalytic hydration of ethene |
|---|---|---|
Raw materials | Glucose, molasses, or other fermentable sugars | Ethene and steam |
Source | Can use renewable biomass | Ethene is commonly obtained from petroleum processing |
Process | Biochemical process using yeast enzymes | Chemical addition reaction |
Conditions | Approximately 30–35°C; absence of oxygen | Approximately 300°C and 60 atm, with an acid catalyst |
Reaction rate | Relatively slow | Fast industrial process |
Product | Dilute ethanol solution requiring purification | Ethanol produced by a continuous industrial process |
23.2 Describe the preparation of ethanol by the fermentation process.
Ethanol can be prepared by fermenting sugar-containing materials with yeast.
1. Preparation of molasses solution
Molasses is diluted with water to obtain a suitable sugar concentration for fermentation.
2. Addition of nutrients and yeast
Suitable nutrients, such as ammonium salts, may be added to support yeast growth. Yeast is introduced, and the temperature is maintained at approximately 30–35°C in the absence of oxygen.
3. Enzymatic reactions
Fermentation takes place in two main stages.
Stage 1: Inversion of sucrose
The enzyme invertase converts sucrose into glucose and fructose.
Stage 2: Conversion of glucose into ethanol
The enzyme system in yeast converts glucose into ethanol and carbon dioxide.
4. Purification
After fermentation, the resulting mixture is separated and purified by distillation. Further distillation can produce concentrated ethanol, commonly around 95% ethanol under ordinary rectification conditions.
23.3 Describe the applications of ethanol in the pharmaceutical and cosmetic industries.
A. Pharmaceutical industry
Solvent: Ethanol dissolves many medicinal substances that are not readily soluble in water.
Preparation of medicines: It is used in certain cough syrups, tinctures, tonics, and liquid medicinal preparations.
Antiseptic and disinfectant: At suitable concentrations, ethanol is used in antiseptic solutions and hand sanitizers to reduce microorganisms on the skin.
B. Cosmetic industry
Perfumes and body sprays: Ethanol acts as a solvent and carrier for fragrances and evaporates quickly after application.
Skin toners: It is used in some toners and astringent preparations to provide a refreshing sensation.
Deodorants: It serves as a solvent and helps fragrances disperse evenly in deodorant products.
Notes by Sir Dilawar
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