Module 2: Chemical Properties of Acids and Bases

 

🌟 Module 2: Chemical Properties of Acids and Bases

Chapter: Acids, Bases and Salts – Class 10 Science (CBSE)

🎯 Objective:

To understand the chemical behaviour of acids and bases with various classes of compounds including metals, metal oxides, metal carbonates, and non-metal oxides, through balanced chemical equations and real-life examples.

🔬 1. Reaction of Acids with Metals

🔹 General Reaction:

$$\text{Acid} + \text{Metal} \rightarrow \text{Salt} + \text{Hydrogen gas (H₂↑)}$$

✅ Example:

$$\text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2↑$$

• Hydrogen gas is evolved – it can be tested by bringing a burning splint near the mouth of the test tube. A ‘pop’ sound confirms hydrogen.

• Salt formed depends on the acid and metal used.

🧠 Concept Insight:

Metals displace hydrogen from acids because they are more electropositive. This is a single displacement reaction.

🧪 2. Reaction of Acids with Metal Carbonates and Bicarbonates

🔹 General Reactions:

$$\text{Acid} + \text{Metal carbonate} \rightarrow \text{Salt} + \text{Carbon dioxide (CO₂)} + \text{Water}$$
$$\text{Acid} + \text{Metal bicarbonate} \rightarrow \text{Salt} + \text{CO}_2 + \text{H}_2O$$

✅ Example 1:

$$\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{CO}_2↑ + \text{H}_2O$$

✅ Example 2:

$$\text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{CO}_2↑ + \text{H}_2O$$

🔍 CO₂ Detection Test:

Pass the evolved gas through lime water (Ca(OH)₂). If it turns milky, CO₂ is present:

$$\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3↓ + \text{H}_2O$$

🔥 3. Reaction of Acids with Metal Oxides (Basic Oxides)

Metal oxides are basic in nature and neutralize acids.

🔹 General Reaction:

$$\text{Acid} + \text{Metal oxide} \rightarrow \text{Salt} + \text{Water}$$

✅ Example:

$$2\text{HCl} + \text{CuO} \rightarrow \text{CuCl}_2 + \text{H}_2O$$

🧠 Concept Insight:
This is a neutralisation reaction where metal oxides act like bases.

🌫️ 4. Reaction of Bases with Non-metal Oxides (Acidic Oxides)

Non-metal oxides like CO₂ are acidic in nature and react with bases.

🔹 General Reaction:

$$\text{Base} + \text{Non-metal oxide} \rightarrow \text{Salt} + \text{Water}$$

✅ Example:

$$\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2O$$

• This reaction also forms insoluble calcium carbonate, making lime water turn milky.

• Indicates that CO₂ behaves as an acidic oxide.

🧪 Activity: Baking Soda and Vinegar Reaction

🎲 Materials:

• Baking soda (sodium bicarbonate – NaHCO₃)

• Vinegar (contains acetic acid – CH₃COOH)

• Transparent glass

• Spoon

🧪 Procedure:

1. Take 1 spoon of baking soda in a glass.

2. Add 2–3 spoons of vinegar.

3. Observe the fizzing and bubble formation.

🔬 Reaction:

$$\text{NaHCO}_3 + \text{CH}_3\text{COOH} \rightarrow \text{CH}_3\text{COONa} + \text{CO}_2↑ + \text{H}_2O$$

💡 Observation:

• CO₂ gas causes fizzing.

• It is the same principle used in baking, where CO₂ causes dough to rise.

📌 Summary of Key Reactions

Reaction Type	Example Equation
Acid + Metal	Zn + HCl → ZnCl₂ + H₂
Acid + Carbonate/Bicarbonate	Na₂CO₃ + HCl → NaCl + CO₂ + H₂O
Acid + Metal Oxide	CuO + HCl → CuCl₂ + H₂O
Base + Non-metal Oxide	Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

🧠 Think Like a Scientist

🔹 Q: Why is CO₂ treated as an acidic oxide?

🔹 A: Because it reacts with bases to form salt and water—just like an acid.

🔹 Q: Why is fizzing seen when vinegar is added to baking soda?

🔹 A: Because CO₂ gas is released due to acid-base neutralisation.

🧠 Misconceptions Cleared

• Not all metal oxides are acidic; metal oxides are generally basic.

• Not all acids react with all metals—unreactive metals like copper do not displace hydrogen from dilute acids like HCl.

• Baking soda is a weak base, not a neutral compound.