Ethanol Fizzes With Sodium Like Water Does, yet Burns Like a Fuel
Prepare ethanol by hydrolysing an alkyl halide, learn its physical properties and why it boils so much higher than a hydrocarbon of similar mass, write its reactions with oxygen, sodium, acetic acid and concentrated sulphuric acid, and tell denatured alcohol, methylated spirit and spurious alcohol apart.
What makes ethanol behave partly like water and partly like a hydrocarbon?
Drop a small piece of sodium into water and it fizzes, releasing hydrogen. Drop the same metal into ethanol and it fizzes too, a little more gently. Yet ethanol also burns with a clean blue flame in a spirit lamp — something water can never do.
**The explanation is in the structure, :
- The group** is like part of a water molecule, . It gives ethanol its water-like behaviour — reacting with sodium and mixing freely with water
- **The group is a hydrocarbon chain. It gives ethanol its fuel-like behaviour — burning to carbon dioxide and water
Ethanol is the most familiar alcohol, and it turns up everywhere:
- Hand sanitisers and many antiseptic solutions
- Medicines, tinctures and perfumes, where it is used as a solvent
- Petrol blended with ethanol, sold at fuel pumps across India
- Alcoholic drinks, where it is the active ingredient
Because it is so useful and so easily obtained, ethanol also raises safety and legal questions. Industrial ethanol is made undrinkable on purpose, and illicit liquor contaminated with methanol, a closely related but highly poisonous alcohol, can cause blindness and death.
This part covers:
- Preparation of ethanol by hydrolysis of an alkyl halide
- Physical properties — nature, solubility, density and boiling point
- Chemical properties — combustion, reaction with sodium, ester formation and dehydration to ethene
- Denatured alcohol, methylated spirit and spurious alcohol, and the uses of ethanol
The link to Part 3. Bromoethane with alcoholic potassium hydroxide gave ethene. With aqueous potassium hydroxide, the same starting material gives ethanol — and ethanol with concentrated sulphuric acid turns back into ethene. The three compounds are joined in a small circle of reactions.**
This page covers the fourth part of the ICSE Class 10 Chemistry chapter on organic chemistry: the preparation, physical and chemical properties, and uses of ethanol, and the types of alcohol sold for different purposes.
**The explanation is in the structure, :
- The group** is like part of a water molecule, . It gives ethanol its water-like behaviour — reacting with sodium and mixing freely with water
- **The group is a hydrocarbon chain. It gives ethanol its fuel-like behaviour — burning to carbon dioxide and water
Ethanol is the most familiar alcohol, and it turns up everywhere:
- Hand sanitisers and many antiseptic solutions
- Medicines, tinctures and perfumes, where it is used as a solvent
- Petrol blended with ethanol, sold at fuel pumps across India
- Alcoholic drinks, where it is the active ingredient
Because it is so useful and so easily obtained, ethanol also raises safety and legal questions. Industrial ethanol is made undrinkable on purpose, and illicit liquor contaminated with methanol, a closely related but highly poisonous alcohol, can cause blindness and death.
This part covers:
- Preparation of ethanol by hydrolysis of an alkyl halide
- Physical properties — nature, solubility, density and boiling point
- Chemical properties — combustion, reaction with sodium, ester formation and dehydration to ethene
- Denatured alcohol, methylated spirit and spurious alcohol, and the uses of ethanol
The link to Part 3. Bromoethane with alcoholic potassium hydroxide gave ethene. With aqueous potassium hydroxide, the same starting material gives ethanol — and ethanol with concentrated sulphuric acid turns back into ethene. The three compounds are joined in a small circle of reactions.**
This page covers the fourth part of the ICSE Class 10 Chemistry chapter on organic chemistry: the preparation, physical and chemical properties, and uses of ethanol, and the types of alcohol sold for different purposes.
How is ethanol prepared by the hydrolysis of an alkyl halide?
Bromoethane or iodoethane boiled with aqueous potassium or sodium hydroxide exchanges its halogen atom for an –OH group, giving ethanol and a potassium or sodium halide.
The reaction. An alkyl halide is boiled under reflux with an aqueous solution of an alkali:
What happens to the molecule. The hydroxide ion replaces the halogen atom on the carbon chain. It is a substitution reaction, and because water provides the medium, it is called hydrolysis.
Worked check — balancing the bromoethane equation.
- Carbon:
- Hydrogen: on the left; on the right
- Oxygen: ; potassium: ; bromine:
Balanced.
Worked example — mass of ethanol. What mass of ethanol can be obtained from of bromoethane? C , H , Br , O .
How ethanol is made on a large scale. The laboratory method uses costly alkyl halides, so industry uses cheaper routes:
- Fermentation of sugars by yeast, from molasses or grain:
- Hydration of ethene, adding water across the double bond with a catalyst:
An everyday example. India's large sugar industry leaves behind molasses, a thick syrup still rich in sugar. Distilleries ferment that molasses to ethanol, much of which is blended into petrol — a by-product of making table sugar turned into fuel.
The boundary case — the solvent decides the product. Bromoethane with aqueous potassium hydroxide gives ethanol by substitution. With alcoholic potassium hydroxide it gives ethene by elimination, as Part 3 showed. **Writing aqueous in the condition is not a detail — it is the difference between two completely different products.**
The reaction. An alkyl halide is boiled under reflux with an aqueous solution of an alkali:
What happens to the molecule. The hydroxide ion replaces the halogen atom on the carbon chain. It is a substitution reaction, and because water provides the medium, it is called hydrolysis.
Worked check — balancing the bromoethane equation.
- Carbon:
- Hydrogen: on the left; on the right
- Oxygen: ; potassium: ; bromine:
Balanced.
Worked example — mass of ethanol. What mass of ethanol can be obtained from of bromoethane? C , H , Br , O .
How ethanol is made on a large scale. The laboratory method uses costly alkyl halides, so industry uses cheaper routes:
- Fermentation of sugars by yeast, from molasses or grain:
- Hydration of ethene, adding water across the double bond with a catalyst:
An everyday example. India's large sugar industry leaves behind molasses, a thick syrup still rich in sugar. Distilleries ferment that molasses to ethanol, much of which is blended into petrol — a by-product of making table sugar turned into fuel.
The boundary case — the solvent decides the product. Bromoethane with aqueous potassium hydroxide gives ethanol by substitution. With alcoholic potassium hydroxide it gives ethene by elimination, as Part 3 showed. **Writing aqueous in the condition is not a detail — it is the difference between two completely different products.**
What are the physical properties of ethanol, and why does it boil so high for its size?
Ethanol is a colourless, volatile liquid with a characteristic smell, less dense than water, completely miscible with water, and boiling at about 78 °C — far higher than a hydrocarbon of similar mass, because its –OH groups attract one another strongly.
Physical properties:
- Nature: a colourless, volatile liquid with a pleasant, characteristic smell and a burning taste
- Solubility: miscible with water in all proportions; also a good solvent for many organic compounds such as oils, resins and dyes
- Density: less than water, about
- Boiling point: about
- Nature towards litmus: neutral — it does not change the colour of either red or blue litmus
Why ethanol boils so much higher than a hydrocarbon. Compare ethanol with propane, a hydrocarbon of almost the same molecular mass.
- **Propane boils at about — it is a gas
- Ethanol boils at about ** — it is a liquid
The masses are almost equal, so size cannot explain the gap. The difference is the group: **the hydrogen of one ethanol molecule's is strongly attracted to the oxygen of a neighbouring molecule. Those attractions must be overcome before ethanol can boil, so its boiling point is far higher.
Why ethanol mixes with water. The same attraction works between ethanol and water molecules**, since water also has groups. Ethanol fits into water's network of attractions, so the two mix in any proportion — while propane, with no group, does not dissolve.
Why ethanol is neutral although it contains an –OH group. The in ethanol is covalently bonded to carbon and does not release hydroxyl ions in water. It is not a base like sodium hydroxide, whose ions are free — so ethanol leaves litmus unchanged.
An everyday example. A few drops of hand sanitiser feel cold on the skin and dry within seconds. Ethanol is volatile, and as it evaporates it takes heat from your hand, leaving a cooling sensation.
The boundary case. Ethanol mixes with water completely, but longer-chain alcohols do not. As the hydrocarbon chain grows, it dominates the small group, so solubility in water falls along the alcohol series — the gradation in properties from Part 2, appearing in a new family.
Physical properties:
- Nature: a colourless, volatile liquid with a pleasant, characteristic smell and a burning taste
- Solubility: miscible with water in all proportions; also a good solvent for many organic compounds such as oils, resins and dyes
- Density: less than water, about
- Boiling point: about
- Nature towards litmus: neutral — it does not change the colour of either red or blue litmus
Why ethanol boils so much higher than a hydrocarbon. Compare ethanol with propane, a hydrocarbon of almost the same molecular mass.
- **Propane boils at about — it is a gas
- Ethanol boils at about ** — it is a liquid
The masses are almost equal, so size cannot explain the gap. The difference is the group: **the hydrogen of one ethanol molecule's is strongly attracted to the oxygen of a neighbouring molecule. Those attractions must be overcome before ethanol can boil, so its boiling point is far higher.
Why ethanol mixes with water. The same attraction works between ethanol and water molecules**, since water also has groups. Ethanol fits into water's network of attractions, so the two mix in any proportion — while propane, with no group, does not dissolve.
Why ethanol is neutral although it contains an –OH group. The in ethanol is covalently bonded to carbon and does not release hydroxyl ions in water. It is not a base like sodium hydroxide, whose ions are free — so ethanol leaves litmus unchanged.
An everyday example. A few drops of hand sanitiser feel cold on the skin and dry within seconds. Ethanol is volatile, and as it evaporates it takes heat from your hand, leaving a cooling sensation.
The boundary case. Ethanol mixes with water completely, but longer-chain alcohols do not. As the hydrocarbon chain grows, it dominates the small group, so solubility in water falls along the alcohol series — the gradation in properties from Part 2, appearing in a new family.
What are the chemical reactions of ethanol with oxygen, sodium, acetic acid and concentrated sulphuric acid?
Ethanol burns to carbon dioxide and water, reacts with sodium to give sodium ethoxide and hydrogen, combines with acetic acid in the presence of concentrated sulphuric acid to form the fruity ester ethyl ethanoate, and is dehydrated by hot concentrated sulphuric acid to ethene.
1. Combustion. Ethanol burns in air with a blue, non-luminous flame and no soot:
2. Action with sodium. Sodium reacts steadily, releasing hydrogen gas:
The product, sodium ethoxide, is a white solid once the excess ethanol evaporates. The reaction is less vigorous than sodium with water.
3. Ester formation — esterification. Ethanol warmed with acetic acid and a few drops of concentrated sulphuric acid forms ethyl ethanoate and water:
- Observation: a sweet, fruity smell — noticed best when the mixture is poured into water
- Role of concentrated sulphuric acid: it acts as a catalyst and removes water, helping the reaction go forward
- The reaction is reversible, shown by the double arrow
4. Dehydration to ethene. Ethanol heated with excess concentrated sulphuric acid at about loses water:
This is the dehydrating action of concentrated sulphuric acid from the sulphuric acid chapter, and the preparation of ethene from Part 3.
Worked check — balancing the combustion equation.
- Carbon:
- Hydrogen: on the left; on the right
- Oxygen: on the left; on the right
Balanced.
Worked example 1 — hydrogen from sodium. What volume of hydrogen at STP is released when of ethanol reacts with excess sodium?
Worked example 2 — the most ester possible. of acetic acid reacts with excess ethanol. What is the largest mass of ethyl ethanoate that could form?
Because the reaction is reversible, the actual yield is less than this maximum.
An everyday example. Spirit lamps in school laboratories and some camping stoves burn ethanol-based fuel. The clean blue flame is the complete combustion equation above.
The boundary case — temperature changes the dehydration product. At about with excess acid, ethanol gives ethene. **At a lower temperature, about , with excess ethanol, two molecules lose one water between them and form diethyl ether**:
Same reagents, different temperature, different product.
1. Combustion. Ethanol burns in air with a blue, non-luminous flame and no soot:
2. Action with sodium. Sodium reacts steadily, releasing hydrogen gas:
The product, sodium ethoxide, is a white solid once the excess ethanol evaporates. The reaction is less vigorous than sodium with water.
3. Ester formation — esterification. Ethanol warmed with acetic acid and a few drops of concentrated sulphuric acid forms ethyl ethanoate and water:
- Observation: a sweet, fruity smell — noticed best when the mixture is poured into water
- Role of concentrated sulphuric acid: it acts as a catalyst and removes water, helping the reaction go forward
- The reaction is reversible, shown by the double arrow
4. Dehydration to ethene. Ethanol heated with excess concentrated sulphuric acid at about loses water:
This is the dehydrating action of concentrated sulphuric acid from the sulphuric acid chapter, and the preparation of ethene from Part 3.
Worked check — balancing the combustion equation.
- Carbon:
- Hydrogen: on the left; on the right
- Oxygen: on the left; on the right
Balanced.
Worked example 1 — hydrogen from sodium. What volume of hydrogen at STP is released when of ethanol reacts with excess sodium?
Worked example 2 — the most ester possible. of acetic acid reacts with excess ethanol. What is the largest mass of ethyl ethanoate that could form?
Because the reaction is reversible, the actual yield is less than this maximum.
An everyday example. Spirit lamps in school laboratories and some camping stoves burn ethanol-based fuel. The clean blue flame is the complete combustion equation above.
The boundary case — temperature changes the dehydration product. At about with excess acid, ethanol gives ethene. **At a lower temperature, about , with excess ethanol, two molecules lose one water between them and form diethyl ether**:
Same reagents, different temperature, different product.
What are denatured alcohol, methylated spirit and spurious alcohol, and what is ethanol used for?
Denatured alcohol is ethanol made unfit to drink by adding poisonous or unpleasant substances, methylated spirit is ethanol denatured mainly with methanol, and spurious alcohol is illicit liquor contaminated with methanol that can cause blindness and death; ethanol is used as a solvent, fuel, antiseptic and raw material.
1. Denatured alcohol. Ethanol to which small amounts of poisonous or unpleasant substances have been added — such as methanol, pyridine or a coloured dye — so that it cannot be drunk.
- Purpose: industrial ethanol is used in huge quantities as a solvent and fuel. Denaturing it prevents misuse as a drink and allows it to be sold for industry without the taxes charged on drinkable alcohol
2. Methylated spirit. Ethanol denatured chiefly with methanol, often with a dye added so it can be recognised.
- Uses: as a solvent, a fuel for spirit lamps and a cleaning agent
- It must never be drunk, because of the methanol it contains
3. Spurious alcohol. Illicit or illegally made liquor that contains methanol, either added deliberately or formed through careless production.
- Why it is so dangerous: in the body, methanol is converted into toxic compounds that damage the optic nerve, causing blindness, and in larger amounts it can cause death
- Methanol looks, smells and tastes much like ethanol, so a person drinking it cannot tell
Worked comparison — ethanol and methanol side by side.
- Ethanol, : molecular mass ; the alcohol in drinks and sanitisers
- Methanol, : molecular mass ; highly poisonous
- Both belong to the same homologous series and differ by one :
Two members of one family, with near-identical physical properties and opposite effects on the body — which is exactly why denaturing works as a warning and why spurious alcohol is so deadly.
4. Uses of ethanol:
- Solvent for medicines, tinctures, perfumes, varnishes, lacquers and dyes
- Fuel — blended with petrol, and in spirit lamps
- Antiseptic — in hand sanitisers and for sterilising skin before injections
- Thermometer liquid — for measuring low temperatures, since it freezes far below the freezing point of water
- Raw material for making acetic acid, esters, ether and other chemicals
- Alcoholic beverages
An everyday example. The surgical spirit a nurse uses to clean the skin before an injection is an alcohol-based antiseptic that is denatured so that it is not drinkable — a daily reminder of both uses of the idea.
The boundary case. Denaturing does not change the ethanol chemically — it adds other substances to it. Denatured alcohol still burns and dissolves things exactly as pure ethanol does, which is why it is perfectly suited to industrial and fuel uses while being dangerous to drink.
1. Denatured alcohol. Ethanol to which small amounts of poisonous or unpleasant substances have been added — such as methanol, pyridine or a coloured dye — so that it cannot be drunk.
- Purpose: industrial ethanol is used in huge quantities as a solvent and fuel. Denaturing it prevents misuse as a drink and allows it to be sold for industry without the taxes charged on drinkable alcohol
2. Methylated spirit. Ethanol denatured chiefly with methanol, often with a dye added so it can be recognised.
- Uses: as a solvent, a fuel for spirit lamps and a cleaning agent
- It must never be drunk, because of the methanol it contains
3. Spurious alcohol. Illicit or illegally made liquor that contains methanol, either added deliberately or formed through careless production.
- Why it is so dangerous: in the body, methanol is converted into toxic compounds that damage the optic nerve, causing blindness, and in larger amounts it can cause death
- Methanol looks, smells and tastes much like ethanol, so a person drinking it cannot tell
Worked comparison — ethanol and methanol side by side.
- Ethanol, : molecular mass ; the alcohol in drinks and sanitisers
- Methanol, : molecular mass ; highly poisonous
- Both belong to the same homologous series and differ by one :
Two members of one family, with near-identical physical properties and opposite effects on the body — which is exactly why denaturing works as a warning and why spurious alcohol is so deadly.
4. Uses of ethanol:
- Solvent for medicines, tinctures, perfumes, varnishes, lacquers and dyes
- Fuel — blended with petrol, and in spirit lamps
- Antiseptic — in hand sanitisers and for sterilising skin before injections
- Thermometer liquid — for measuring low temperatures, since it freezes far below the freezing point of water
- Raw material for making acetic acid, esters, ether and other chemicals
- Alcoholic beverages
An everyday example. The surgical spirit a nurse uses to clean the skin before an injection is an alcohol-based antiseptic that is denatured so that it is not drinkable — a daily reminder of both uses of the idea.
The boundary case. Denaturing does not change the ethanol chemically — it adds other substances to it. Denatured alcohol still burns and dissolves things exactly as pure ethanol does, which is why it is perfectly suited to industrial and fuel uses while being dangerous to drink.
Exam tip
What earns full marks in an ethanol answer?
Give the condition for every reaction, name every product, and state observations — especially for the ester and the sodium reaction.
- Write aqueous KOH or NaOH for the preparation from an alkyl halide, and say the reaction is hydrolysis
- List physical properties with values: colourless volatile liquid, boiling point about 78 °C, density less than water, miscible with water, neutral to litmus
- Explain the high boiling point by the attraction between –OH groups, not by molecular mass
- Write the balanced combustion equation with three oxygen molecules
- Name sodium ethoxide and hydrogen as products with sodium
- For esterification, mention concentrated sulphuric acid, warming, the fruity smell and the double arrow
- Give the dehydration condition: excess concentrated sulphuric acid at about 170 °C
- Define denatured alcohol, methylated spirit and spurious alcohol separately
- Say why methanol is dangerous — blindness and death
- List at least four uses of ethanol
The misconception to name. Ethanol is not a base just because it contains an –OH group. Its –OH is covalently bonded and does not ionise, so it is neutral to litmus. Calling ethanol alkaline confuses a functional group with a hydroxide ion.
A second trap. Writing ethene as the product of bromoethane with aqueous KOH. Aqueous KOH gives ethanol; alcoholic KOH gives ethene — the solvent must be stated and matched to the product.
- Write aqueous KOH or NaOH for the preparation from an alkyl halide, and say the reaction is hydrolysis
- List physical properties with values: colourless volatile liquid, boiling point about 78 °C, density less than water, miscible with water, neutral to litmus
- Explain the high boiling point by the attraction between –OH groups, not by molecular mass
- Write the balanced combustion equation with three oxygen molecules
- Name sodium ethoxide and hydrogen as products with sodium
- For esterification, mention concentrated sulphuric acid, warming, the fruity smell and the double arrow
- Give the dehydration condition: excess concentrated sulphuric acid at about 170 °C
- Define denatured alcohol, methylated spirit and spurious alcohol separately
- Say why methanol is dangerous — blindness and death
- List at least four uses of ethanol
The misconception to name. Ethanol is not a base just because it contains an –OH group. Its –OH is covalently bonded and does not ionise, so it is neutral to litmus. Calling ethanol alkaline confuses a functional group with a hydroxide ion.
A second trap. Writing ethene as the product of bromoethane with aqueous KOH. Aqueous KOH gives ethanol; alcoholic KOH gives ethene — the solvent must be stated and matched to the product.
Did you know
Why is ethanol blended into the petrol sold at Indian fuel pumps?
The petrol sold at many fuel pumps across India contains ethanol. The ethanol is not an impurity; it has been deliberately blended in, and the chemistry of this lesson explains why.
1. Ethanol is a fuel in its own right. It burns completely with a clean flame:
Mixing it into petrol replaces part of the fuel that would otherwise come from crude oil, much of which India imports.
2. Ethanol can be made from crops. The fermentation equation from this lesson turns sugars into ethanol:
Sugarcane molasses, surplus grain and other farm produce can all supply that sugar, so the fuel can be grown again each season rather than pumped from the ground once.
3. Ethanol already contains oxygen. Its molecule has an oxygen atom, which helps the fuel burn more completely in an engine and can reduce the carbon monoxide produced by incomplete combustion.
4. The carbon has a shorter journey. The carbon dioxide released when crop-based ethanol burns was taken from the air only recently, when the plants grew by photosynthesis — unlike the carbon in petrol, which was locked underground for a very long time.
But the properties from this lesson also create challenges.
- Ethanol mixes completely with water, so blended fuel must be stored carefully to keep moisture out
- Ethanol releases less energy per litre than petrol, so blending changes how far a vehicle travels on a tankful
- Engines and fuel pipes must be compatible with ethanol, which can affect some rubber and plastic parts
**So a litre of blended petrol brings together fermentation, combustion, solubility in water and the structure of the group** — nearly every idea in this part of the chapter.
1. Ethanol is a fuel in its own right. It burns completely with a clean flame:
Mixing it into petrol replaces part of the fuel that would otherwise come from crude oil, much of which India imports.
2. Ethanol can be made from crops. The fermentation equation from this lesson turns sugars into ethanol:
Sugarcane molasses, surplus grain and other farm produce can all supply that sugar, so the fuel can be grown again each season rather than pumped from the ground once.
3. Ethanol already contains oxygen. Its molecule has an oxygen atom, which helps the fuel burn more completely in an engine and can reduce the carbon monoxide produced by incomplete combustion.
4. The carbon has a shorter journey. The carbon dioxide released when crop-based ethanol burns was taken from the air only recently, when the plants grew by photosynthesis — unlike the carbon in petrol, which was locked underground for a very long time.
But the properties from this lesson also create challenges.
- Ethanol mixes completely with water, so blended fuel must be stored carefully to keep moisture out
- Ethanol releases less energy per litre than petrol, so blending changes how far a vehicle travels on a tankful
- Engines and fuel pipes must be compatible with ethanol, which can affect some rubber and plastic parts
**So a litre of blended petrol brings together fermentation, combustion, solubility in water and the structure of the group** — nearly every idea in this part of the chapter.
Exam relevance
How does the chemistry of ethanol lead into JEE and NEET?
This is foundation work for Class 12 Alcohols, Phenols and Ethers and Class 12 Haloalkanes and Haloarenes, both examined in JEE Main and NEET Chemistry, and for hydrogen bonding in Class 11 Chemical Bonding and Molecular Structure.
Where the preparation leads. Class 12 covers the preparation of alcohols from haloalkanes, by hydration of alkenes and by fermentation. **The substitution of a halogen by with aqueous alkali is analysed there through nucleophilic substitution mechanisms, and the competing elimination with alcoholic alkali is a recurring question.
Where the physical properties lead. The high boiling point and water solubility of ethanol are explained in Class 11 and Class 12 by hydrogen bonding. Arranging alcohols, ethers and hydrocarbons of similar mass in order of boiling point is a standard question type, and the ethanol–propane comparison on this page is exactly that reasoning.
Where the reactions lead. Class 12 Alcohols, Phenols and Ethers treats the reaction of alcohols with sodium as evidence of their weakly acidic nature, esterification with carboxylic acids, and dehydration — giving ethene at a higher temperature and diethyl ether at a lower one. The temperature-dependent products** are asked directly, often in Kelvin, where about is about and about is about .
Where esterification leads. The reversible formation of esters links to Class 11 Equilibrium and to the reactions of carboxylic acids in Class 12, including the role of the acid catalyst.
Where methanol toxicity leads. The difference between methanol and ethanol, and the uses of alcohols, appear as factual objective items, particularly in NEET.
Question types to expect. At this level: preparation, properties, reactions with conditions and definitions. In competitive papers: substitution versus elimination, boiling-point orders through hydrogen bonding, dehydration products at different temperatures, and the acidity of alcohols compared with water and phenol.
The single trap that costs marks. Mixing up the two dehydration products. Higher temperature with excess acid gives ethene; lower temperature with excess ethanol gives diethyl ether. Options that swap the temperatures are common.
A second trap. Treating the –OH of ethanol as basic. Alcohols are very weakly acidic, not basic, as their reaction with sodium to release hydrogen shows — a point both exams use in assertion-reason questions.
Board versus competitive emphasis. The ICSE paper marks equations with conditions, physical properties and definitions of alcohol types; a competitive paper marks mechanisms, orders and product predictions. The transferable habit is reading every condition — aqueous or alcoholic, higher or lower temperature — before choosing a product.
Where the preparation leads. Class 12 covers the preparation of alcohols from haloalkanes, by hydration of alkenes and by fermentation. **The substitution of a halogen by with aqueous alkali is analysed there through nucleophilic substitution mechanisms, and the competing elimination with alcoholic alkali is a recurring question.
Where the physical properties lead. The high boiling point and water solubility of ethanol are explained in Class 11 and Class 12 by hydrogen bonding. Arranging alcohols, ethers and hydrocarbons of similar mass in order of boiling point is a standard question type, and the ethanol–propane comparison on this page is exactly that reasoning.
Where the reactions lead. Class 12 Alcohols, Phenols and Ethers treats the reaction of alcohols with sodium as evidence of their weakly acidic nature, esterification with carboxylic acids, and dehydration — giving ethene at a higher temperature and diethyl ether at a lower one. The temperature-dependent products** are asked directly, often in Kelvin, where about is about and about is about .
Where esterification leads. The reversible formation of esters links to Class 11 Equilibrium and to the reactions of carboxylic acids in Class 12, including the role of the acid catalyst.
Where methanol toxicity leads. The difference between methanol and ethanol, and the uses of alcohols, appear as factual objective items, particularly in NEET.
Question types to expect. At this level: preparation, properties, reactions with conditions and definitions. In competitive papers: substitution versus elimination, boiling-point orders through hydrogen bonding, dehydration products at different temperatures, and the acidity of alcohols compared with water and phenol.
The single trap that costs marks. Mixing up the two dehydration products. Higher temperature with excess acid gives ethene; lower temperature with excess ethanol gives diethyl ether. Options that swap the temperatures are common.
A second trap. Treating the –OH of ethanol as basic. Alcohols are very weakly acidic, not basic, as their reaction with sodium to release hydrogen shows — a point both exams use in assertion-reason questions.
Board versus competitive emphasis. The ICSE paper marks equations with conditions, physical properties and definitions of alcohol types; a competitive paper marks mechanisms, orders and product predictions. The transferable habit is reading every condition — aqueous or alcoholic, higher or lower temperature — before choosing a product.
Key takeaways
What must you be able to do from this part?
One preparation, five physical properties, four reactions, three kinds of alcohol and a list of uses.
- Preparation: , aqueous alkali — hydrolysis
- ** of bromoethane** gives of ethanol
- Industrially: fermentation of sugars, , and hydration of ethene
- Physical properties: colourless volatile liquid, characteristic smell, density about , boiling point about , miscible with water, neutral to litmus
- **Boils about higher than propane of similar mass, because –OH groups attract each other
- Combustion**: , blue flame
- With sodium: ; of ethanol gives of hydrogen
- Esterification: , concentrated sulphuric acid, fruity smell
- Dehydration: excess concentrated sulphuric acid at about gives ethene; at about with excess ethanol, diethyl ether
- Denatured alcohol: ethanol made undrinkable with methanol, pyridine or dye
- Methylated spirit: ethanol denatured mainly with methanol
- Spurious alcohol: illicit liquor containing methanol — causes blindness and death
- Uses: solvent, fuel, antiseptic, thermometer liquid, raw material for chemicals, beverages
The sharpest self-test is a circle of three compounds. Write the reactions that turn bromoethane into ethanol, ethanol into ethene, and bromoethane directly into ethene, each with its exact condition — then explain in one line why two of them start from the same compound but end differently.
- Preparation: , aqueous alkali — hydrolysis
- ** of bromoethane** gives of ethanol
- Industrially: fermentation of sugars, , and hydration of ethene
- Physical properties: colourless volatile liquid, characteristic smell, density about , boiling point about , miscible with water, neutral to litmus
- **Boils about higher than propane of similar mass, because –OH groups attract each other
- Combustion**: , blue flame
- With sodium: ; of ethanol gives of hydrogen
- Esterification: , concentrated sulphuric acid, fruity smell
- Dehydration: excess concentrated sulphuric acid at about gives ethene; at about with excess ethanol, diethyl ether
- Denatured alcohol: ethanol made undrinkable with methanol, pyridine or dye
- Methylated spirit: ethanol denatured mainly with methanol
- Spurious alcohol: illicit liquor containing methanol — causes blindness and death
- Uses: solvent, fuel, antiseptic, thermometer liquid, raw material for chemicals, beverages
The sharpest self-test is a circle of three compounds. Write the reactions that turn bromoethane into ethanol, ethanol into ethene, and bromoethane directly into ethene, each with its exact condition — then explain in one line why two of them start from the same compound but end differently.