Acidity and indicators | Year 7 Chemistry (Cambridge) PDF Download

Introduction to Acids and Alkalis

• Acids and alkalis are common substances with distinct properties.
• Acids: Examples include hydrochloric acid (found in stomachs), sulfuric acid (in car batteries), and citric acid (in citrus fruits like lemons).
• Alkalis: Examples include sodium hydroxide (in cleaning products and soaps) and potassium hydroxide (in soaps).

Properties of Acids and Alkalis

• Acids: Sour taste; can be corrosive or irritant. Examples: vinegar, fizzy drinks.
• Alkalis: Soapy feel; can be corrosive or irritant. Examples: soap, bleach.

Safety with Acids and Alkalis

• Some acids and alkalis are safer (e.g., vinegar, soaps) while others are more dangerous (e.g., car battery acids, cleaning products).
• Protective equipment like gloves and goggles may be required when handling stronger acids and alkalis.

Chemical Symbols and Composition

• Acids: Typically start with hydrogen in their chemical formulas (e.g., HCl for hydrochloric acid, H₂SO₄ for sulfuric acid).
• Alkalis: Often end with hydroxide in their formulas (e.g., NaOH for sodium hydroxide).

Using Indicators to Identify Acids and Alkalis

• Colorless solutions of acids and alkalis can be identified using universal indicator.
• Acids: Turn universal indicator colors like red, orange, or yellow (pH range 0-6).
• Alkalis: Turn universal indicator colors like green, blue, or purple (pH range 8-14).
• pH 7 is neutral, neither acidic nor alkaline.

Strength of Acids and Alkalis

• pH scale ranges from 0 (strong acids) to 14 (strong alkalis).
• Weak Acids: Examples include tea and coffee (pH close to neutral).
• Strong Acids: Examples include vinegar (pH around 2) and stomach acid.
• Weak Alkalis: Everyday items like toothpaste and soap (pH close to neutral).
• Strong Alkalis: Examples like bleach (pH higher, towards 14).

Conclusion

• Understanding acids and alkalis helps in identifying their properties and uses in everyday life.
• The pH scale and universal indicator are crucial tools in distinguishing between acids and alkalis based on their strength and characteristics.