Grade 6 (age 11-12)

Acids & Bases

Some things around us are acidic and taste sour, like vinegar, while others feel slippery and are basic, like soap. pH is a number for how acidic or basic something is: 7 is neutral, lower is acidic, and higher is basic. Here you can slide the pH, test indicators, and add base to an acid to watch it neutralize.

What are Acids and Bases?

pH7

🧪 Acids and Bases

①Acids taste sour (vinegar, lemon, soda)

②Bases feel slippery (soap, detergent)

③Neutral: neither acid nor base (pure water)

④pH 7 is neutral; lower = acidic, higher = basic

Using Indicators

🔬 Indicators

①Blue litmus → turns red in acid

②Red litmus → turns blue in base

③BTB: acid=yellow, neutral=green, base=blue

④Phenolphthalein: only turns pink in base

Neutralization

Base added20%

💡 Neutralization

①Acid (H⁺) + base (OH⁻) → water

②Acidity weakens, approaches neutral

③Antacids work by neutralizing stomach acid

④Bee sting (acid) → ammonia (base) is also neutralization

Summary

Acids and Bases

pH 0–6: acidic / pH 7: neutral / pH 8–14: basic

Lower pH = stronger acid; higher = stronger base

Neutralization

Acid(H⁺) + Base(OH⁻) → Water(H₂O) + Salt

Acid and base cancel each other out

🎯 Key Points

①Acid: sour, pH < 7, blue litmus → red

②Base: slippery, pH > 7, red litmus → blue

③Neutral: pH = 7, pure water

④Indicators distinguish acids/bases

⑤Neutralization: acid + base → water + salt

Examples and Unit Test

Example 1

A solution has pH 3. Is it acidic, neutral, or basic?

pH 7 is neutral; below 7 is acidic and above 7 is basic.

pH 3 is below 7, so it is acidic.

▸ Acidic

Lower pH is more acidic, higher pH is more basic. Vinegar and lemon juice are acidic.

Example 2

BTB solution turns yellow in a liquid. What is the liquid, and what happens to blue litmus paper dipped in it?

BTB is yellow in acid, green in neutral, and blue in base.

Yellow means acidic, and acid turns blue litmus red.

▸ Acidic / blue litmus → red

Indicator colors let you tell acids from bases.

Unit-test style

Which statement about acids and bases is correct?

①A higher pH means a stronger acid

②An acidic solution turns blue litmus red

③Pure water has pH 14

④When an acid and a base meet, a stronger acid forms

⑤BTB solution turns blue in acid

▸ ② An acidic solution turns blue litmus red

Acid turns blue litmus red; base turns red litmus blue.

Higher pH is basic (①), pure water is pH 7 (③), an acid and base neutralize each other (④), and BTB is yellow in acid (⑤).

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