What is the pH scale and what does it measure?

The pH scale measures the concentration of H⁺ ions in a solution, ranging from 0 to 14. pH 7 is basic/alkaline (NaOH ≈14). Lower pH = stronger acid; higher pH = stronger base.

What are the differences between acids and bases?

Acids: sour taste, turns blue litmus red, pH 7, produces OH⁻ ions, e.g., NaOH, Ca(OH)₂. Neutralisation of acid + base → salt + water.

What is the importance of pH in daily life?

pH matters in: (1) Digestion — stomach maintains pH 1-3 for HCl to function. (2) Tooth decay — bacteria produce acid, pH below 5.5 causes enamel erosion. (3) Agriculture — crops need soil pH 6-7. (4) Blood — maintained at 7.35-7.45; deviation causes illness. (5) Acid rain — pH below 5.6 damages ecosystems.

pH Scale and Indicators

Acids, Bases and Salts • Class 10 Science • NCERT • CBSE

The pH scale measures how acidic or basic a solution is, ranging from 0 to 14. Values below 7 are acidic, 7 is neutral, and above 7 are basic/alkaline. Indicators like litmus, phenolphthalein, and methyl orange are used to test the pH of solutions.

Key Formulas

Acid + Base → Salt + Water (Neutralisation)
Acid + Metal → Salt + H₂ gas
Acid + Metal carbonate → Salt + CO₂ + Water
pH < 7: Acidic; pH = 7: Neutral; pH > 7: Basic

Frequently Asked Questions

What is the pH scale and what does it measure?: The pH scale measures the concentration of H⁺ ions in a solution, ranging from 0 to 14. pH < 7 is acidic (lemon juice ≈2), pH = 7 is neutral (pure water), pH > 7 is basic/alkaline (NaOH ≈14). Lower pH = stronger acid; higher pH = stronger base.
What are the differences between acids and bases?: Acids: sour taste, turns blue litmus red, pH < 7, produces H⁺ ions, e.g., HCl, H₂SO₄. Bases: bitter taste, soapy feel, turns red litmus blue, pH > 7, produces OH⁻ ions, e.g., NaOH, Ca(OH)₂. Neutralisation of acid + base → salt + water.
What is the importance of pH in daily life?: pH matters in: (1) Digestion — stomach maintains pH 1-3 for HCl to function. (2) Tooth decay — bacteria produce acid, pH below 5.5 causes enamel erosion. (3) Agriculture — crops need soil pH 6-7. (4) Blood — maintained at 7.35-7.45; deviation causes illness. (5) Acid rain — pH below 5.6 damages ecosystems.

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