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Ethanol (C₂H₅OH) and Ethanoic Acid (CH₃COOH)

Key Point 1: Ethanol – Physical and Chemical Properties

Physical Properties

  • Ethanol is a clear, colorless, and volatile liquid.
  • It has a pleasant odor and gives a burning taste if tasted (not recommended).
  • Its boiling point is about 78°C, which is lower than the boiling point of water (100°C).
  • Ethanol mixes with water in any proportion. This is due to hydrogen bonding.
  • It is highly volatile and evaporates quickly at room temperature.

Examples:

  1. Laboratory Setup: If you leave a beaker of ethanol open in the lab, it will evaporate faster than water.
  2. Sanitizer: Most hand sanitizers contain ethanol. The cooling on your hand when sanitizer dries is due to ethanol's volatility.
  3. Solvent Use: Ethanol is commonly used to dissolve chemicals in the lab, such as in perfumes or medicines.

Chemical Properties

a) Reaction with Sodium

  • Ethanol reacts with sodium (Na) to form sodium ethoxide and hydrogen gas.
  • Equation:
    2C2H5OH+2Na→2C2H5ONa+H2↑2C_2H_5OH + 2Na \rightarrow 2C_2H_5ONa + H_2 \uparrow

Example:

  1. Lab Reaction: Add a small piece of sodium in ethanol – bubbles of hydrogen are seen.
  2. Demonstration: Bubbles rise and the solution contains sodium ethoxide.

b) Combustion

  • Ethanol burns in the presence of oxygen to release carbon dioxide, water, and energy.
  • Equation:
    C2H5OH+3O2→2CO2+3H2O+EnergyC_2H_5OH + 3O_2 \rightarrow 2CO_2 + 3H_2O + \text{Energy}

Examples:

  1. Spirit lamps in laboratories use ethanol as fuel; they burn with a blue flame.
  2. Ethanol-blended petrol ignites in engines during combustion.

c) Dehydration

  • When heated with concentrated sulfuric acid, ethanol loses water to form ethene (an alkene).
  • Equation:
    C2H5OH→conc.H2SO4, ΔC2H4+H2OC_2H_5OH \xrightarrow{conc.H_2SO_4,\ \Delta} C_2H_4 + H_2O

Examples:

  1. Lab Activity: Heating ethanol with sulfuric acid produces a gas (ethene) that decolorizes bromine water.
  2. Industrial Use: This method is used in the production of ethene from ethanol.

d) Oxidation

  • When oxidized with strong oxidizers such as acidic K₂Cr₂O₇ or KMnO₄, ethanol converts to ethanoic acid.
  • Equation:
    C2H5OH+[O]→CH3COOH+H2OC_2H_5OH + [O] \rightarrow CH_3COOH + H_2O

Examples:

  1. Chemical Test: Add ethanol to acidified potassium dichromate; the solution changes from orange to green, showing oxidation.
  2. Everyday Life: This reaction explains how alcoholic drinks turn sour.

Key Point 2: Uses of Ethanol

  1. Beverages: Ethanol is the alcohol in drinks such as beer, wine, whisky.

    • Example: Beer (4-8% ethanol) and Wine (about 12%).
    • Example: Drinking whisky is consuming a mixture with up to 40% ethanol.

  2. Fuel: Used as a fuel alone or mixed with petrol.

    • Example: Ethanol-blended petrol (E10, which is 10% ethanol) reduces vehicle pollution.
    • Example: Spirit lamps in laboratories.

  3. Antiseptic: Ethanol is in sanitizers and wipes because it kills germs.

    • Example: Hand sanitizer during the COVID-19 pandemic.
    • Example: Medical swabs use ethanol to clean skin before injections.

Key Point 3: Ethanoic Acid (CH₃COOH) – Physical and Chemical Properties

Physical Properties

  • Colorless liquid with a pungent, vinegar-like smell.
  • Tastes sour.
  • Boiling point: 118°C.
  • Freezing Point: 16.7°C. Below this, it solidifies, called Glacial acetic acid.
  • Highly soluble in water.

Examples:

  1. Kitchen Vinegar: The sour taste and smell of vinegar.
  2. Winter Day: Ethanoic acid forms ice-like crystals in a cold lab – students see “glacial” acetic acid.
  3. Dilute in Water: When you add ethanoic acid to water, no layers form—it's completely soluble.

Chemical Properties

a) Acidic Nature

  • Ethanoic acid is a weak acid; it partially ionizes in water to give H⁺ ions.
  • Equation:
    CH3COOH⇌CH3COO−+H+CH_3COOH \rightleftharpoons CH_3COO^- + H^+

Examples:

  1. Litmus Test: Blue litmus paper turns red with ethanoic acid—shows it’s acidic.
  2. pH Testing: Ethanoic acid solution has a pH around 3-4.

b) Reaction with Metals

  • Reacts with active metals (like sodium, zinc) to give hydrogen gas.
  • Equation:
    2CH3COOH+2Na→2CH3COONa+H2↑2CH_3COOH + 2Na \rightarrow 2CH_3COONa + H_2 \uparrow

Examples:

  1. Lab Test: Add sodium to ethanoic acid—fizzing hydrogen gas is seen.
  2. Real-life: Acidic foods in metal containers sometimes cause gas bubbles.

c) Reaction with Carbonates and Bicarbonates

  • Produces carbon dioxide gas.
  • Equation:
    2CH3COOH+Na2CO3→2CH3COONa+CO2↑+H2O2CH_3COOH + Na_2CO_3 \rightarrow 2CH_3COONa + CO_2 \uparrow + H_2O

Examples:

  1. Kitchen Test: Adding vinegar (acetic acid) to baking soda (NaHCO₃) creates bubbles of CO₂.
  2. Cleaning: Vinegar removes lime-scale from kettles because it reacts with calcium carbonate, producing fizz.

d) Neutralization (Reaction with Base)

  • Ethanoic acid reacts with bases (like NaOH) to form a salt (acetate) and water.
  • Equation:
    CH3COOH+NaOH→CH3COONa+H2OCH_3COOH + NaOH \rightarrow CH_3COONa + H_2O

Examples:

  1. Lab Titration: Neutralizing vinegar with sodium hydroxide in an experiment.
  2. Food Preserving: Acetic acid can neutralize basic substances during food preparation.

e) Esterification

  • Reacts with alcohol (like ethanol) in the presence of concentrated sulfuric acid to form an ester with a fruity smell.
  • Equation:
    CH3COOH+C2H5OH→conc.H2SO4CH3COOC2H5+H2OCH_3COOH + C_2H_5OH \xrightarrow{conc.H_2SO_4} CH_3COOC_2H_5 + H_2O
  • This produces ethyl ethanoate, which smells like pineapple.

Examples:

  1. Fruity Flavors: The smell of raspberry or banana essence is from esters like ethyl ethanoate.
  2. Classroom Experiment: Mixing ethanol and ethanoic acid with a little sulfuric acid and warming releases a sweet, fruity scent.

Key Point 4: Uses of Ethanoic Acid

  1. Vinegar: A 5-8% solution of acetic acid in water is vinegar.

    • Example: Used to preserve pickles.
    • Example: Added to salads for taste.

  2. Food Preservative: Helps in preserving foods by making the environment acidic.

    • Example: Used in commercial packaged foods.
    • Example: Used in pickles and chutneys at home.

  3. Industrial Use: Used to manufacture chemicals, acetates, dyes, and plastics.

    • Example: Cellulose acetate for making photographic films.
    • Example: Sodium acetate used in heating pads.

  4. Medicinal Use: Dilute solutions used as antiseptics (e.g., for ear drops).

Key Point 5: Differences between Ethanol and Ethanoic Acid

PropertiesEthanol (C₂H₅OH)Ethanoic Acid (CH₃COOH)
NatureAlcoholCarboxylic Acid
OdorPleasant, fruityPungent, vinegar-like
pHNearly neutral (about 7)Acidic (about 3-4)
TasteBurning, a bit sweetSour
Reaction with NaLiberates H₂ (gas)Liberates H₂ (gas)
Reaction with BaseNo reactionForms salt & water

Examples:

  1. Smell Test: Smell a drop of each (with caution); ethanol is pleasant, ethanoic acid is sharp and pungent.
  2. Litmus Paper Test: Ethanol does not change blue litmus, ethanoic acid turns blue litmus red.
  3. Reaction with NaOH: Ethanoic acid reacts with NaOH to form sodium acetate and water, while ethanol shows no reaction.

Activity: Action of Acetic Acid on Sodium Bicarbonate

Objective:

To test if a liquid sample is acetic acid by checking if it reacts with sodium bicarbonate to produce carbon dioxide.

Materials:

  • Test tube
  • Dropper
  • Acetic acid (vinegar)
  • Sodium bicarbonate (baking soda)

Steps:

  1. Take a small quantity (about 2 mL) of acetic acid in a test tube.
  2. Add a pinch of sodium bicarbonate to the test tube.
  3. Observe the reaction.

Observations:

  • Effervescence (bubbles) is seen due to carbon dioxide gas.
  • This confirms the acidic nature of ethanoic acid.

Explanation:

Acetic acid reacts with sodium bicarbonate forming sodium acetate, water, and carbon dioxide.

Equation:
CH3COOH+NaHCO3→CH3COONa+H2O+CO2↑CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2 \uparrow

Fun Twist:

Blow up a balloon by fitting it over the test tube before adding sodium bicarbonate. The CO₂ generated will fill the balloon!

Scenario-based Questions

Scenario 1:
You spill some sanitizer on your hand and notice it dries quickly and gives a cooling sensation.

  • Question: Why does ethanol in the sanitizer evaporate so fast, and why do you feel cool?
  • Answer: Ethanol is highly volatile, so it evaporates quickly. The evaporation absorbs heat from your skin, giving a cooling sensation.

Scenario 2:
Your mother adds vinegar to a salad.

  • Question: What is the role of ethanoic acid in vinegar for the salad?
  • Answer: Ethanoic acid gives the salad a sour taste and can act as a mild preservative by inhibiting the growth of bacteria.

Scenario 3:
In the lab, your teacher asks you to distinguish between ethanol and ethanoic acid using a chemical test.

  • Question: Which test would you perform, and what would you observe?
  • Answer: I would use blue litmus paper. Ethanoic acid turns it red due to its acidic nature, while ethanol does not change the color.

Scenario 4:
You want to create a fruity-smelling liquid in the lab.

  • Question: Which two chemicals would you mix and what catalyst is needed?
  • Answer: I would mix ethanol and ethanoic acid with a few drops of concentrated sulfuric acid as a catalyst to form ethyl ethanoate, which smells fruity....

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