Properties Of Acetic Acid

MATERIALS REQUIRED

Glass rod, acetic acid, litmus paper, sodium bicarbonate, test tubes, water, test tube stand, lime water.

THEORY

(i) Acetic acid is an organic acid, its 5-8% concentrated solution is called vinegar.

(ii) It is a weak acid. It ionises partially in presence of water as shown below:

CH₃COOH + H₂O ⇋ CH₃COO^-(aq) + H₂O⁺(aq)

(iii) Acetic acid has pH <7, hence It turns blue litmus red.

(iv) It is completely soluble in water.

(v) It reacts with sodium bicarbonate to liberate CO_2, which turns lime water milky and the milkiness disappears if an excess of CO₂ is passed through the solution.

PROCEDURE

1. Odour

Take a small amount of acetic acid in a test tube.

2.Solubility in water

Take 2 mL of water in a test tube and add a few drops of acetic acid. Shake the test tube carefully.

3.Effect on litmus

Take a strip of blue litmus paper and add one drop of acetic solution on the blue litmus paper.

Take a red litmus paper and add one drop of acetic acids solution on red litmus paper.

4.Reaction with sodium bicarbonate

Take 5 mL of acetic acid in a test tube and add sodium bicarbonate.

Pass the evolving gas through lime water.

OBSERVATIONS

RESULT

1. Acetic acid has a pungent odour.

2. Acetic acid is completely soluble in water i.e. acetic acid and water form a true solution.

3. Acetic acid having a pH <7 turns blue litmus paper red.
4. Acetic acid does not change the colour of blue litmus paper.

PRECAUTIONS

1. Do not inhale vapours of acetic acid directly.

2. Ethanoic acid should be handled with care.

3. Freshly prepared lime water solution should be used.

(a) When acetic acid is reacted with distilled water, it gets dissolved in distilled water forming a homogeneous transparent solution.

(b) When acetic acid is reacted with sodium hydrogen carbonate powder, brisk effervescence due to CO₂ gas is observed.

On reacting lime water with CO₂, it turns milky due to formation of insoluble white precipitate of calcium carbonate.

Acetic acid is used:

(a) In manufacture of rayon fibre.

(b) as coagulant in the manufacture of rubber.

Note: coagulant- a substance/ agent which is added to thicken a mixture.

Litmus test helps in proving the acidic nature of acetic acid as it turns blue litmus red and does not affect red litmus paper.

Acetic acid doesn’t dissociate much in solution. It partially ionizes in water which means not all of its molecules break up into positive and negative ions when dissolved in water.

It can be tested by lime water test. The gas is allowed to pass through lime water and if it turns milky, then the liberated gas is CO₂.

Yes, acetic acid is used as a preservative. It preserves food products for longer use.

Two physical properties of acetic acid are:

(a) It has a vinegar like smell.

(b) It is soluble in water.

When a few drops of acetic acid are added to a test tube containing phenolphthalein, the phenolphthalein remains colourless due to the acidic medium.

Note: Phenolphthalein is an indicator which turns colourless in acidic media and pinkish red in basic media.

Vinegar is 5-8 % aqueous solution of acetic acid. It is used to add flavour to food and also used as a preservative.

Pure acetic acid is known as glacial acetic acid. It is undiluted acetic acid.

Yes, acetic acid is miscible in water in all proportions. Its miscibility makes it a useful industrial chemical.

Acetic acid is prepared naturally by bacterial fermentation. These bacteria are found in foodstuffs, soil, etc.

Some of the medical uses of acetic acid are as follows:

(a) It is used as an antiseptic.

(b) It is used in screening of some cancers.

(c) It can also be used to treat cancers.

Acetic acid is corrosive to some metals to metals like iron, zinc, magnesium, etc. It can become flammable at temperatures exceeding 39^o C.