Chemical Properties of Acids, Bases and Salts
Chemistry helps us understand how substances react and change during chemical processes. One of the most important topics in Class 10 Science Chapter – Acids, Bases and Salts is the Chemical Properties of Acids, Bases and Salts. These substances show different reactions with metals, metal carbonates, bases, acids, and indicators.
Acids, bases, and salts are commonly found in daily life. Lemon juice, vinegar, soap, baking soda, and table salt are examples of acidic, basic, and salt substances used every day.These reactions are important in Class 10 chemistry and are often asked in exams
1.01. Chemical Properties of Acids
An acid is a substance that dissociates in an aqueous solution to produce hydrogen ions (H⁺) or hydronium ions (H₃O⁺). These ions drive the following reactions:
A. Reaction with Metals
Acids react with active metals (like Zinc, Magnesium, and Iron) to form a salt and release Hydrogen gas (H₂).
- General Word Equation: Acid + Metal -> Salt + Hydrogen Gas
- When zinc granules are treated with dilute sulfuric acid, bubbles of hydrogen gas form.
Zn (s) + H₂SO₄ (aq) -> ZnSO₄ (aq) + H₂ (g) - The Soap Bubble Pop Test: If you pass this gas through a soap solution, bubbles form. Bringing a burning candle near these gas-filled bubbles results in a distinctive "pop" sound, confirming the presence of Hydrogen gas.
B. Reaction with Metal Carbonates and Metal Hydrogen Carbonates
Acids react with metal carbonates (like Na₂CO₃) and metal hydrogen carbonates (like NaHCO₃) to produce a salt, water, and Carbon Dioxide gas (CO₂).
- Metal Carbonate/Bicarbonate + Acid -> Salt + Water + Carbon Dioxide
- Key Chemical Equations:
Na₂CO₃ (s) + 2HCl (aq) -> 2NaCl (aq) + H₂O (l) + CO₂ (g)
NaHCO₃ (s) + HCl (aq) -> NaCl (aq) + H₂O (l) + CO₂ (g) - The Lime Water Test: To confirm a gas is CO₂, pass it through clear lime water [Ca(OH)₂]. The lime water turns milky due to the formation of an insoluble white precipitate of Calcium Carbonate (CaCO₃).
Ca(OH)₂ (aq) + CO₂ (g) -> CaCO₃ (s) ↓ + H₂O (l)
(Note: If you keep passing excess CO₂ into the solution, the milkiness completely disappears as soluble calcium hydrogen carbonate forms).
C. Reaction with Metal Oxides
Metal oxides are basic in nature. Therefore, acids react with metal oxides to form salt and water.
- Metal Oxide + Acid -> Salt + Water
- Example: Black copper oxide reacts with hydrochloric acid to form a blue-green solution of copper chloride.
CuO (s) + 2HCl (aq) -> CuCl₂ (aq) + H₂O (l)
2.02. Chemical Properties of Bases
Bases are substances that produce hydroxyl ions (OH⁻) when dissolved in water (water-soluble bases are called alkalis). They exhibit the following properties:
A. Reaction with Metals
Bases do not react with all metals. They only react with certain amphoteric metals (like Zinc and Aluminum) to liberate Hydrogen gas.
- General Word Equation: Base + Metal -> Salt + Hydrogen Gas
- Crucial Exam Equation: Zinc reacts with hot, concentrated sodium hydroxide to form Sodium Zincate and hydrogen gas.
2NaOH (aq) + Zn (s) -> Na₂ZnO₂ (aq) + H₂ (g)
B. Reaction with Non-Metal Oxides
Non-metal oxides (like CO₂ or SO₂) are acidic in nature. When they react with a base, they form salt and water.
- General Word Equation: Base + Non-Metal Oxide -> Salt + Water
- Example: The lime water test itself is a direct example of this reaction:
Ca(OH)₂ (aq) + CO₂ (g) -> CaCO₃ (s) + H₂O (l)
3.03. The Neutralization Reaction (Acids + Bases)
When an acid mixes with a base, they neutralize each other's effects. The H⁺ ions from the acid combine with the OH⁻ ions from the base to form water, leaving behind an ionic salt.
- General Word Equation: Acid + Base -> Salt + Water
- Chemical Equation Example:
HCl (aq) + NaOH (aq) -> NaCl (aq) + H₂O (l) - Ionic View of the Reaction: H⁺ (aq) + OH⁻ (aq) -> H₂O (l)
4.04. Chemical Nature of Salts
Salts are not always neutral. Their chemical properties and pH depend on the relative strengths of the parent acid and base from which they were created: