9.3 Corrosive Properties of Concentrated Acids and Alkali

• Corrosive Nature:

• Concentrated acids and concentrated alkali are highly corrosive.

• They can damage clothes, skin, and eyes.

• If concentrated acids or alkali come into contact with the body, the affected area must be cleaned repeatedly.

• After cleaning, inform a teacher about the contact.

• Dilution of Concentrated Acids and Alkali:

• Concentrated acids and alkali should be added slowly to water.

• This process turns them into dilute solutions as they dissolve completely.

Individual Task: Experiment of Strong and Weak Acids or Strong and Weak Alkali

Experiment with Strong Acid (Hydrochloric Acid) vs. Weak Acid (Ethanoic Acid):

• Materials:

• 50 mL dilute hydrochloric acid (HCl) in a beaker.

• Graphite rods (2).

• A battery and wires.

• A light bulb.

• Procedure:

1. Set two graphite rods in the beaker with hydrochloric acid, ensuring they don’t touch each other.

2. Connect one graphite rod to one edge of the battery with a wire.

3. Connect the other graphite rod to the other edge of the battery, routing the wire through a light bulb.

4. The bulb should light up. Observe the brightness of the light.

• Next Step:

1. Take some ethanoic acid in another beaker. Ethanoic acid is a weak acid.

2. Set up the same apparatus with graphite rods in the ethanoic acid.

3. Again, connect the battery and light bulb in the same manner.

4. The bulb will light up. Observe the brightness.

• Result:

• The brightness of the bulb in the hydrochloric acid beaker will be brighter than the one in the ethanoic acid beaker.

• Explanation:

• Strong acids release more H+ ions (protons) in an aqueous solution, allowing more electricity to pass through the solution. This causes the bulb to glow brighter.

• Weak acids release fewer H+ ions, resulting in less electrical conductivity, and the bulb glows dimmer.

Strong vs. Weak Alkali Experiment:

• Strong Alkali (Sodium Hydroxide, NaOH) vs. Weak Alkali (Ammonium Hydroxide, NH4OH):

• Set up similar experiments with NaOH and NH4OH solutions.

• The bulb in the NaOH solution will light up brighter than in the NH4OH solution.

• Conclusion:

• NaOH is a strong alkali, and NH4OH is a weak alkali because NaOH dissociates more completely, producing more hydroxide ions (OH-) and conducting more electricity.

Key Points to Remember:

• Weak Acid → Lesser amount of H+ (protons) produced.

• Strong Acid → Greater amount of H+ (protons) produced.

• Weak Alkali → Lesser amount of OH- produced.

• Strong Alkali → Greater amount of OH- produced.

This experiment demonstrates the relationship between the strength of acids/alkalis and their ability to conduct electricity, based on the concentration of ions in solution.