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Syllabus

Ethanol

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Topics

  • Physical Properties
  • Chemical Properties
  • Uses and Significance
  • Experiment

Physical Properties

Ethanol (C₂H₅OH) is a colourless liquid at room temperature. Commonly known as alcohol or spirit, it is completely miscible with water and is neutral to litmus paper.

Physical Properties of Ethanol

Property Value / Description
Appearance Colourless, transparent liquid
Odour Mild, characteristic alcohol-like smell
Melting Point –114.1°C
Boiling Point 78.37°C
Density 0.789 g/cm³ at 20°C
State at Room Temp. Liquid
Flash Point 13°C (closed cup)
Solubility (in Water) Completely miscible in all proportions
Solubility (in Organics) Miscible with most organic solvents
Miscibility Mixes well with water and solvents in all proportions
Hydrogen Bonding Forms strong intermolecular hydrogen bonds
pH (neutral solution) Approximately 7 (neutral)
Vapour Pressure 5.95 kPa at 20°C
Viscosity 1.2 mPa·s at 20°C
Surface Tension 22.3 mN/m at 20°C
Heat of Combustion –1366.8 kJ/mol
Heat of Evaporation 38.56 kJ/mol

 

Chemical Properties

(i) Reaction with Sodium: Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas:

2Na + 2CH₃CH₂OH → 2CH₃CH₂ONa + H₂↑

This reaction occurs due to the –OH functional group in ethanol, despite it being neutral.

(ii) Dehydration Reaction: When heated with concentrated sulphuric acid at 170°C, ethanol loses a water molecule and forms ethene:

\[\begin{array}{cc}
\phantom{}\ce{\underset{}{CH3 - CH2 - OH} ->[(170°C)][conc.H2SO4] \underset{(ethanoic acid)}{CH2 = CH2 - H2O}}\
\end{array}\]

Uses and Significance

  1. Ethanol is used as a solvent in medicines like tincture iodine and cough syrups.
  2. It plays a role in extraction processes in laboratories and industries.
  3. Ethanol serves as a fuel and is blended with petrol to make gasohol, which improves fuel efficiency and reduces pollution.
  4. It burns cleanly, producing only carbon dioxide and water, making it eco-friendly and renewable.
  5. Ethanol is the main intoxicating agent in alcoholic beverages.
  6. It affects the central nervous system and can impair body functions.
  7. Pure ethanol (absolute alcohol) is toxic and may be fatal if consumed.
 

Experiment

1. Aim: To observe the reaction of ethanol with sodium and magnesium and detect the release of hydrogen gas.

2. Requirements: Big test tube, a delivery tube with a rubber cork, a candle, a knife, ethanol, sodium metal, and magnesium ribbon.

3. Procedure

  • Add 10 ml of ethanol to a big test tube.
  • Cut small pieces of sodium metal and add them to the ethanol.
  • Immediately close the test tube with the rubber cork and delivery tube.
  • Bring a lit candle near the end of the delivery tube and observe.
  • Repeat the process using a magnesium ribbon instead of sodium.

4. Observations

  • With sodium: Hydrogen gas is released and burns with a pop sound. Sodium pieces appear to dance on the ethanol surface due to the hydrogen gas bubbles forming rapidly.
  • With magnesium: No reaction or gas bubbles are observed.

5. Conclusion

  • Sodium reacts with ethanol, releasing hydrogen gas and forming sodium ethoxide.
  • Ethanol, though neutral, reacts due to its -OH functional group.
  • Magnesium does not react with ethanol, as it is less reactive and ethanol is not acidic.

Reaction: 2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂↑

(Ethanol + Sodium → Sodium ethoxide + Hydrogen gas)

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Video Tutorials

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Shaalaa.com | Carbon and Compounds part 25 (Ethanol)

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