What Do All Acids and All Bases Have in Common?

In this section, we explore the fundamental characteristics of acids and bases. We will discuss activites that illustrate their behaviors, their properties, and how they interact with water.

Key Point 1: Acids Produce Hydrogen Ions (H⁺)

All acids generate hydrogen ions (H⁺) when dissolved in water. This feature is what makes them acidic.

Activity and Observations

1. Setup: Place nails in a cork connected to a battery and switch.
2. With Acids: When using dilute HCl and dilute H₂SO₄, the bulb glows bright. This means an electric current passes through the solution.
3. With Glucose and Alcohol: The bulb does not glow, indicating no electric current.

Conclusion

Electric current passes through acidic solutions because they dissociate into ions, which carry the current. Glucose and alcohol don’t produce ions, hence do not conduct electricity.

• Example 1: Hydrochloric acid (HCl) produces H⁺ and Cl⁻ ions in solution.
• Example 2: Sulfuric acid (H₂SO₄) produces H⁺, SO₄²⁻ in solution.
• Example 3: Acetic acid (CH₃COOH) produces H⁺, CH₃COO⁻ in solution.

---

Key Point 2: Bases Produce Hydroxide Ions (OH⁻)

Bases release hydroxide ions (OH⁻) when dissolved in water.

Activity and Observations

1. Setup: In a test tube, mix NaCl with concentrated sulfuric acid.
2. Gas Production: Gas is produced and collected.
3. Litmus Test: Wet blue litmus paper turns red, indicating the presence of acid.

Conclusion

This activity shows that HCl produces H⁺ in the presence of water, and without water, H⁺ ions do not dissociate, making HCl not behave like an acid.

• Example 1: Sodium hydroxide (NaOH) produces Na⁺ and OH⁻ ions in solution.
• Example 2: Potassium hydroxide (KOH) produces K⁺ and OH⁻ ions in solution.
• Example 3: Magnesium hydroxide (Mg(OH)₂) produces Mg²⁺ and OH⁻ ions in solution.

---

Key Point 3: The Neutralization Reaction

When an acid reacts with a base, it leads to neutralization, producing salt and water.

Conclusion of the neutralization reaction:

1. Equation: Acid + Base → Salt + Water
2. Specifics of the Reaction: H⁺(aq) + OH⁻(aq) → H₂O(l)

• Example 1: HCl + NaOH → NaCl + H₂O
• Example 2: H₂SO₄ + Ca(OH)₂ → CaSO₄ + 2H₂O
• Example 3: CH₃COOH + KOH → CH₃COOK + H₂O

---

Key Point 4: Conductivity of Aqueous Solutions

Acids are conductive in aqueous solutions because they yield ions.

Explanation

1. Why Aqueous: Acidic and alkaline solutions create charged ions (H⁺ and OH⁻), allowing electricity to flow.
2. Conductivity: The bulbs glowing during activity shows proof of electric conductivity in acids.

---

Key Point 5: Safe Mixing of Acids and Water

Always add acids to water rather than the other way around. This ensures safety.

Reason for Safety:

1. Exothermic Reaction: Mixing concentrated acid with water releases substantial heat.
2. Risk of Splashing: Water added to acid may cause a violent reaction, leading to splashes.

• Observation: When H₂SO₄ is added to water, the temperature increases significantly.

---

Scenario-Based Questions and Answers

1. Scenario: You and your friends are performing the Activity 2.8 with acids and glucose.

   • Question: Why does the bulb glow with acids but not glucose?
   • Answer: The bulb glows with acids because they ionize to produce H⁺, leading to electric conductivity. Glucose does not ionize, so no current flows.

2. Scenario: You ask about the behavior of acids and bases in a chemistry lab.

   • Question: What happens when sodium hydroxide is mixed with hydrochloric acid?
   • Answer: They neutralize each other, producing water and sodium chloride, which is a salt.

3. Scenario: You want to know about safely handling concentrated acids.

   • Question: What is the proper method for diluting concentrated sulfuric acid?
   • Answer: Always add sulfuric acid to water slowly while constantly stirring to avoid splashing and heat buildup.

4. Scenario: You notice that when dry HCl gas is produced, it does not change the color of dry litmus paper.

   • Question: Why is this the case?
   • Answer: Dry HCl gas doesn’t ionize unless dissolved in water; therefore, it does not show acidity with dry litmus.

5. Scenario: You're curious about the properties of concentrated vs. dilute acid.

   • Question: How does diluting an acid affect H₃O⁺ ion concentration?
   • Answer: Diluting an acid decreases the concentration of H₃O⁺ ions per unit volume, as the acid is spread in a larger amount of water.

---