Acids, Bases & Salts

You encounter acids and bases every day -- the citric acid in lemons, the lactic acid in yogurt, the sodium hydroxide in soap. Understanding their chemistry helps you make sense of everyday phenomena and prepares you for deeper chemistry in Grade 11.

What Are Acids and Bases?

Acids produce hydrogen ions (H+) when dissolved in water. They taste sour and turn blue litmus red.

Examples: Hydrochloric acid (HCl), Sulfuric acid (H2SO4), Citric acid (in lemons)

Bases produce hydroxide ions (OH-) when dissolved in water. They taste bitter, feel slippery, and turn red litmus blue.

Examples: Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)2), Ammonia (NH3)

The pH Scale

The pH scale ranges from 0 to 14 and measures how acidic or basic a solution is.

• pH < 7: Acidic (lower = more acidic)
• pH = 7: Neutral (pure water)
• pH > 7: Basic/Alkaline (higher = more basic)

Common pH values: Lemon juice is about 2, vinegar is about 3, pure water is 7, baking soda is about 9, bleach is about 12.

Strong vs. Weak Acids and Bases

• Strong acids (HCl, H2SO4, HNO3) completely dissociate in water -- all molecules split into ions
• Weak acids (citric acid, acetic acid) only partially dissociate
• Strong bases (NaOH, KOH) completely dissociate
• Weak bases (NH3) only partially dissociate

Neutralization

Acid + Base -> Salt + Water

This is called a neutralization reaction because the acid and base cancel each other's properties.

Example: HCl + NaOH -> NaCl + H2O (hydrochloric acid + sodium hydroxide -> common salt + water)

Example: H2SO4 + 2KOH -> K2SO4 + 2H2O

Indicators

Indicators are substances that change color depending on pH:

• Litmus: Red in acid, blue in base
• Phenolphthalein: Colorless in acid, pink in base
• Methyl orange: Red in acid, yellow in base
• Turmeric (haldi): Yellow in acid, reddish-brown in base

Nepal Connection: Nepali farmers test soil pH to determine which crops will grow best. The acidic soils of the hills are good for tea (like Ilam tea), while the more neutral soils of the Terai suit rice and wheat.

Key Takeaways

• Acids produce H+ ions; bases produce OH- ions
• pH scale: 0-14, with 7 being neutral
• Strong acids/bases fully dissociate; weak ones partially dissociate
• Neutralization: acid + base = salt + water