CBSE Notes Class 10 Science Chapter 2 - Acids Bases and Salts

Acids and bases are like the dynamic duo of chemistry! Acids release hydrogen ions (H⁺) in water, have a sour taste, a pH below 7, and turn blue litmus paper red. Bases release hydroxide ions (OH⁻), have a bitter taste, a pH above 7, and turn red litmus paper blue. Both react to form salts and water in neutralization reactions. Examples include HCl (acid) and NaOH (base). Let’s understand acids, bases and salts in detail. 

1.0Properties of Acids and Bases

Acids:

• Taste sour and change blue litmus paper to red.
• Highly reactive with metals and release hydrogen gas.
• Common acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and acetic acid (CH₃COOH).

Bases:

• Taste bitter and feel slippery.
• Change red litmus paper to blue and are less reactive with metals than acids.
• Examples include sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂), and ammonia (NH₃).

2.0What are Salts and How are They Formed?

Salts are ionic compounds composed of positive ions (cations) from a base and negative ions (anions) from an acid. The formation of salts occurs through the neutralization reaction between an acid and a base.

3.0Difference between Acid, Base and Salt

Here is an image showing how Litmus and pH paper show color changes in acidic and basic solutions to indicate pH levels.

4.0Common Reactions Involving Acids and Bases

• Neutralization: 

Acid + Base → Salt + Water 

e.g., HCl + NaOH → NaCl + H₂O

• Reaction with Metals: 

Acid + Metal → Salt + Hydrogen Gas 

e.g., 2HCl + Zn → ZnCl₂ + H₂

• Reaction with Carbonates: 

Acid + Carbonate → Salt + Water + Carbon Dioxide 

e.g., 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂

5.0Dissociation of Acids and Bases in Water

Acids:

• Strong Acids (e.g., HCl, H₂SO₄, HNO₃) almost completely dissociate in water, releasing a high concentration of hydrogen ions (H⁺), which results in a highly acidic solution.
• Weak Acids (e.g., CH₃COOH) partially dissociate, releasing fewer hydrogen ions into the solution.

Bases:

• Strong Bases (e.g., NaOH, KOH) fully dissociate in water, releasing a large number of hydroxide ions (OH⁻), making the solution highly basic.
• Weak Bases (e.g., NH₃) dissociate partially, producing fewer hydroxide ions in the solution.

6.0Measuring the Strength of Acid or Base Solutions

The strength of acid or base solutions is typically measured using the pH scale:

• pH Scale: Ranges from 0 to 14, where 7 is neutral (pure water). pH values less than 7 indicate acidic solutions, while values greater than 7 indicate basic solutions. The closer the pH is to 0, the stronger the acid; the closer the pH is to 14, the stronger the base.
• pOH Scale: Similarly, the pOH of a solution is another scale used to measure the alkalinity of a solution. Just like the pH scale, a lower pOH means a stronger base.
• Concentration: The concentration of H⁺ ions in an acidic solution or OH⁻ ions in a basic solution also indicates strength. This is often expressed in moles per liter (Molarity).

7.0Common salt

The common salt we use every day is a key ingredient for making various products like sodium hydroxide, baking soda, washing soda, and bleaching powder. Let's explore how this one substance can create so many different compounds in brief-