Studying the properties of acetic acid (ethanoic acid)

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Aim

To study the following properties of acetic acid (ethanol acid):

Odour

Solubility in water

Effect on litmus

Reaction with sodium bicarbonate

Apparatus and Chemicals

• Test tube
• Test tube stand
• Acetic acid
• Red and blue litmus paper or solution
• Sodium bicarbonate

Principle

When pure, acetic acid is a colourless liquid in summer but freezes to an ice-like solid in winter as its melting point is 16.7 °C. It has a typical vinegar like odour. It is miscible with water in all proportions.

Acetic acid turns blue litmus red as it is an acid. It liberates CO₂ from carbonates and bicarbonates. For example, a brisk effervescence is produced when a solution of NaHCO₃ is added to acetic acid.
NaHCO₃ + CH₃COOH → CH₃COONa + H₂O + CO₂
The CO₂ so produced can be tested with lime water. It will turn lime water milky.
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
On passing an excess of CO₂ the solution becomes clear.
CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂

Procedure

• Take acetic acid in a clean and dry test tube. Observe its colour and smell. It is colourless ans has a typical, strong vinegar like Odour.
• Take 2-3 drops of acetic acid in a clean and dry test tube. Add 3-5 drops of water and shake well. A clear solution is obtained. Thus acetic acid is miscible with water in all proportions.
• Add 2-3 drops of blue litmus solution to 2-5 mL of acetic acid in a test tube. The blue litmus solution will turn red. Repeat the experiment with red litmus solution. No change in colour is observed.
• Add a pinch of solid sodium bicarbonate to 2-3 drops of acetic acid in a test tube. A brisk effervescence is produced with the liberation of colourless, odourless gas. Pass the gas through lime water. Lime water first turns milky and then becomes clear. The gas evolved is CO₂. Acetic acid liberates CO₂ from bicarbonates.

Observation Table

S.No.	Test/Experiment	Observation	Inference
1.	Smell: Smell the sample of ethanoic acid (acetic acid)	It has vinegar like odour.	Acetic acid has vinegar like odour.
2.	Solubility Test Try to dissolve 2-3 drops of ethanoic acid (acetic acid) in 3-5 drops of water.	It is freely soluble in water.	Acetic acid is miscible with water in all proportions.
3.	Litmus test (a) Add 2-3 drops of blue litmus solution to 2-5 mL of acetic acid in a test tube. (b) Add 2-3 drops of red litmus solution to 2-5 mL of acetic acid in a test tube.	(a) Blue colour of litmus changes to red. (b) No change in colour is produced.	Acetic acid is acidic in nature.
4.	Reaction with sodium hydrogen carbonates (sodium bicarbonate) (a) Add a pinch of sodium bicarbonate to 2-3 drops of acetic acid in a test tube. (b) Pass the gas produced through lime water.	(a) A colourless, odourless gas is produced with brisk effervescence. (b) Lime water first turns milky and on passing more gas, It becomes clear.	Acetic acid liberates CO2 when treated with sodium bicarbonate.

Precautions

• Clean the apparatus thoroughly before the experiment.
• Lime water used should be fresh.

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