5.3 Alcohol
Alcohol is an organic carbon compound composed of carbon, hydrogen, and oxygen elements. It is widely prepared by the fermentation of glucose or starch through yeast action, followed by distillation to purify the ethanol. Alcohol is extensively used as a fuel, solvent, antiseptic, and reactant in industry, but its excessive consumption has severe physical, social, and psychological effects on human health.
Learning Objectives
- Define alcohol as an organic carbon compound containing carbon, hydrogen, and oxygen.
- Describe the preparation of ethanol in the laboratory through the fermentation of glucose using yeast and separation through distillation.
- State the physical properties of alcohol and investigate its chemical properties (combustion and esterification).
- Explain the uses of alcohol in daily life as a fuel, medicine, cosmetics, and industrial solvent.
- Describe the adverse effects of excessive alcohol consumption on human health and body organs.
Laboratory Preparation of Ethanol via Fermentation and Fractional Distillation
Trace the complete path from yeast converting sugar solution to ethanol and carbon dioxide, followed by Liebig condenser distillation at 78°C.
Short Explanation
Definition
Alcohol is an organic carbon compound containing carbon, hydrogen, and oxygen elements.
In the school laboratory, ethanol is produced by fermenting glucose with yeast, where the enzyme zymase converts glucose into ethanol and carbon dioxide. Because fermentation produces a mixture containing water, yeast cells, and ethanol, fractional distillation is used to isolate ethanol at its boiling point of \(78^\circ\text{C}\).
Preparation of ethanol. Food containing glucose or starch, such as sugar, grapes, apples, sugarcane, rice, wheat, potato, and barley, is fermented by yeast. The enzyme zymase converts glucose into ethanol and carbon dioxide. The carbon dioxide produced turns limewater cloudy.
Separation through distillation. Distillation separates ethanol from the fermentation mixture based on the difference in boiling points between ethanol (\(78^\circ\text{C}\)) and water (\(100^\circ\text{C}\)). Pure ethanol distillate is collected at \(78^\circ\text{C}\). The collected distillate is colourless and has a distinctive alcohol smell.
Physical Properties of Alcohol
- Colourless liquid at room temperature.
- Has a distinctive smell.
- Boiling point increases when its number of carbon atoms increases.
- Solubility in water decreases when its number of carbon atoms increases.
Chemical Properties of Alcohol
Combustion
Alcohol burns completely in oxygen or air with a blue flame without soot. The products of combustion are carbon dioxide and water. Carbon dioxide is confirmed by limewater turning cloudy; water is confirmed by dry blue cobalt chloride paper turning pink.
Esterification
Ethanol reacts with ethanoic acid in the presence of concentrated sulphuric acid as a catalyst to produce an ester (ethyl ethanoate) and water. The ester formed has a sweet or fruity smell and is insoluble in water, forming an oily layer floating on water.
Uses of Alcohol in Daily Life
Fuel
Highly flammable, burns with a blue flame, and produces complete and clean combustion without soot. Used as biofuel for motorised vehicles, for example in the Philippines.
Medicine
Used as an antiseptic and disinfectant to kill microorganisms before injections, and as a solvent for various medicines.
Cosmetics
Used as a solvent in perfumes, lotions, and lipsticks.
Industry
Used as a solvent to dissolve organic substances for liquid cleaners and food, and as a reactant in the formation of esters used in food processing, cosmetics, and paints. Ethanediol is a type of alcohol used as an antifreeze in industries.
Effects of Excessive Alcohol Consumption
Excessive alcohol intake damages vital organs and causes serious social and developmental problems.
Excessive alcohol consumption causes addiction, leading to family breakdown and social crimes. Drunk driving causes fatal road accidents and altercations. Expectant mothers consuming excess alcohol give birth to babies with Foetal Alcohol Syndrome: small-sized heads and brains, abnormal facial features, and stunted growth.
| Body Part | Adverse Effect |
|---|---|
| Brain | Damage to brain cells, compromised coordination and nervous system cause disruptions to body balance and difficulty in estimating distance. |
| Eyes | Blurred vision. |
| Lungs | Increased rate of breathing. |
| Heart | Increased rate of heartbeat, high blood pressure. |
| Stomach | Irritation to stomach wall causes bleeding and ulcers. |
| Liver | Damage to liver cells, cells die and harden, cirrhosis, and liver cancer. |
| Kidney | Kidney damage due to overactive elimination of waste substances. |
| Urinary Bladder | Frequent urination. |
Try to Answer First
Answer in your mind, then press “Check Answer”.
Name the enzyme present in yeast that converts glucose into ethanol and carbon dioxide during fermentation.
Why is ethanol distillate collected specifically at \(78^\circ\text{C}\) during distillation?
What is the function of concentrated sulphuric acid in the esterification reaction between ethanol and ethanoic acid?
Common Mistakes
- Confusing the temperature at which ethanol boils (\(78^\circ\text{C}\)) with that of water (\(100^\circ\text{C}\)).
- Forgetting to mention that carbon dioxide turns limewater cloudy, mistakenly testing it with a glowing wooden splinter instead.
- Stating that concentrated sulphuric acid is a reactant in esterification, rather than identifying it as a catalyst.
- Mixing up the physical properties of ester (sweet/fruity smell, insoluble in water) with alcohol (distinctive alcohol smell, soluble in water).
Concept Misunderstandings
Fermentation produces 100% pure ethanol directly in the conical flask.
Fermentation only produces a dilute mixture of ethanol, water, and yeast; distillation is strictly required to separate pure ethanol based on its boiling point.
All alcohols have the same boiling point and solubility.
Boiling point increases as the number of carbon atoms increases, whereas solubility in water decreases as the carbon chain length increases.
Summary
- Alcohol contains carbon, hydrogen, and oxygen.
- It is prepared via yeast fermentation of carbohydrates catalysed by zymase, yielding ethanol and carbon dioxide, followed by distillation at \(78^\circ\text{C}\).
- Alcohols are colourless, volatile liquids that undergo clean, sootless combustion and esterification to form fruity esters.
- Though indispensable as biofuels, antiseptics, and solvents, excessive alcohol intake damages the nervous system, liver, and foetal development.
Short Activity
A. Objective Quiz
1 Which gas is released during the fermentation of glucose that turns limewater cloudy?
2 What are the products formed during the complete combustion of ethanol?
B. Fill in the Blanks
3 In the esterification process, ethanol reacts with ethanoic acid in the presence of concentrated sulphuric acid to produce a sweet-smelling substance called an .
4 Ethanol is separated from the fermentation mixture through distillation because ethanol has a boiling point of °C.
C. Drag and Drop: Match the Body Part to Its Adverse Effect
Drag each body part or condition to the correct adverse effect of excessive alcohol consumption. On a phone, tap an answer first, then tap a matching box. Tap the Answer Choices area to return a selected item.
C. Match the Body Part to Its Adverse Effect
Write the correct body part or condition next to each adverse effect.
| Adverse Effect | Body Part / Condition |
|---|---|
| 1. Compromised coordination, loss of body balance, and difficulty estimating distance | |
| 2. Hardening of dead cells leading to cirrhosis and liver cancer | |
| 3. Irritation of the wall causing bleeding and ulcers | |
| 4. Stunted growth, abnormal face, and small-sized head and brain |
Answer choices: Brain • Liver • Stomach • Foetus
