Acids, Bases and Salts
Overview
Acids, Bases and Salts form a foundational chemistry topic for GTET Paper-2, appearing consistently in the Science section. This topic connects everyday substances (lemon juice, soap, baking soda) to chemical principles, making it both practically relevant and conceptually important for upper primary teaching.
For the exam, you must understand the characteristic properties of acids and bases, how indicators help identify them, the neutralisation reaction that produces salts, and the common applications of these substances. Questions typically test identification of acidic/basic substances, indicator colour changes, salt formation reactions, and practical uses. Mastering this topic also builds the foundation for understanding chemical reactions and environmental chemistry.
The NCERT Class 7 and Class 8 Science textbooks cover this topic thoroughly, and GTET questions align closely with that treatment level—focusing on observable properties, simple reactions, and real-world connections rather than complex calculations.
---
Key Concepts
- **Acids** are substances that taste sour, turn blue litmus red, and release hydrogen ions (H⁺) when dissolved in water. Examples: hydrochloric acid (HCl), sulphuric acid (H₂SO₄), citric acid in lemon.
- **Bases** are substances that taste bitter, feel soapy, turn red litmus blue, and release hydroxide ions (OH⁻) in water. Examples: sodium hydroxide (NaOH), calcium hydroxide (slaked lime), magnesium hydroxide.
- **Indicators** are substances that show different colours in acidic and basic solutions. Natural indicators include litmus, turmeric, and China rose; synthetic indicators include methyl orange and phenolphthalein.
- **Neutralisation** is the reaction between an acid and a base to form salt and water. This reaction releases heat (exothermic). General equation: Acid + Base → Salt + Water.
- **Salts** are ionic compounds formed from neutralisation reactions. The type of salt depends on which acid and base react. Example: HCl + NaOH → NaCl + H₂O.
- **pH Scale** measures how acidic or basic a solution is, ranging from 0 to 14. pH 7 is neutral, below 7 is acidic, above 7 is basic.
- **Strong vs Weak**: Strong acids/bases dissociate completely in water (HCl, NaOH); weak acids/bases dissociate partially (acetic acid, ammonia).
---
Formulas / Key Facts
| Fact | Detail | |------|--------| | Litmus source | Lichen (a plant) | | Blue litmus + Acid | Turns red | | Red litmus + Base | Turns blue | | Turmeric + Base | Turns red/brown | | Phenolphthalein + Base | Turns pink | | Phenolphthalein + Acid | Remains colourless | | Methyl orange + Acid | Turns red | | Methyl orange + Base | Turns yellow | | pH of pure water | 7 (neutral) | | pH of lemon juice | Approximately 2 (acidic) | | pH of soap solution | Approximately 9-10 (basic) |