Acids, Bases, and the pH Scale

🔷 What are Acids and Bases?

Chemicals can be classified into acids, bases (alkalis), or neutral substances, depending on their properties and how they react in water.

🧨 Acids

Feature	Description
Taste	Sour (⚠️ do not taste in lab!)
pH range	0–6.9 (below 7)
In water	Release hydrogen ions (H⁺)
Reaction	React with metals, carbonates, and bases
Litmus paper	Turns blue → red
Examples	Hydrochloric acid (HCl), lemon juice (citric acid), vinegar (acetic acid)

🧼 Bases (Alkalis)

Feature	Description
Taste	Bitter
Feel	Slippery or soapy
pH range	7.1–14 (above 7)
In water	Release hydroxide ions (OH⁻)
Reaction	Neutralize acids
Litmus paper	Turns red → blue
Examples	Sodium hydroxide (NaOH), baking soda, ammonia

🧪 Neutral Substances

Feature	Description
pH value	Exactly 7
Litmus paper	No color change
Examples	Pure water, salt solutions

🌡️ The pH Scale

The pH scale measures how acidic or basic a substance is.
It ranges from 0 to 14:

 0       7       14
 |-------|--------|
 Acid    Neutral  Base

pH < 7 → Acid
pH = 7 → Neutral
pH > 7 → Base

📏 A small change in pH means big change in acidity/basicity (it’s logarithmic).

🎯 Examples of Substances on the pH Scale

Substance	pH Level	Type
Battery acid	1	Strong acid
Lemon juice	2–3	Acid
Vinegar	~3	Acid
Pure water	7	Neutral
Baking soda	8–9	Weak base
Soap	10–11	Base
Bleach	13	Strong base

⚖️ Neutralization Reaction

When an acid reacts with a base, they cancel each other out, forming:

Salt + Water

🧪 Example:

HCl (acid) + NaOH (base) → NaCl (salt) + H₂O (water)

This process is called neutralization and is used in:

Medicine (e.g., antacids)
Agriculture (adjusting soil pH)
Industry (wastewater treatment)

✅ Summary

Acids = sour, pH < 7, give H⁺ ions
Bases = bitter/soapy, pH > 7, give OH⁻ ions
Neutral = pH = 7 (like pure water)
pH scale measures acidity or alkalinity (0–14)
Acid + Base → Salt + Water (neutralization)