AQA GCSE FOUNDATION Chemistry: Acids and Alkalis

Acids and Alkalis: A Foundation Chemistry Tutorial

This tutorial explores the fundamental concepts of acids and alkalis, focusing on pH, indicators, and neutralization.

What are Acids and Alkalis?

Acids and alkalis (also called bases) are two important types of chemicals found in many everyday substances. Here's a simple breakdown:

• Acids: Have a sour taste, react with metals to produce hydrogen gas, and turn litmus paper red. Examples include lemon juice, vinegar, and stomach acid.
• Alkalis: Have a bitter taste, feel slippery, and turn litmus paper blue. Examples include baking soda, soap, and bleach.

pH Scale: Measuring Acidity and Alkalinity

The pH scale is a numerical scale used to measure the acidity or alkalinity of a solution. It ranges from 0 to 14, with:

• 0-6: Acidic solutions
• 7: Neutral solution (like pure water)
• 8-14: Alkaline (or basic) solutions

The lower the pH value, the stronger the acid. Conversely, the higher the pH value, the stronger the alkali.

Indicators: Detecting Acidity and Alkalinity

Indicators are substances that change color depending on the pH of a solution. This allows us to determine whether a substance is acidic, alkaline, or neutral.

• Litmus paper: Turns red in acidic solutions and blue in alkaline solutions.
• Universal indicator: A mixture of several indicators that changes color through a range of pH values.
  • Red: Strong acid
  • Orange: Weak acid
  • Yellow: Slightly acidic
  • Green: Neutral
  • Blue: Slightly alkaline
  • Purple: Strong alkali

Neutralization: Balancing Acids and Alkalis

Neutralization is a chemical reaction where an acid and an alkali react to form salt and water. This reaction cancels out the acidic and alkaline properties, resulting in a neutral solution (pH of 7).

Example:

Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) ? Sodium chloride (NaCl) + Water (H2O)

In this example, hydrochloric acid (a strong acid) reacts with sodium hydroxide (a strong alkali) to produce sodium chloride (a salt) and water. The resulting solution is neutral.

Key Takeaways

• Acids have a sour taste, react with metals, and turn litmus paper red.
• Alkalis have a bitter taste, feel slippery, and turn litmus paper blue.
• The pH scale measures acidity and alkalinity, with 0-6 being acidic, 7 being neutral, and 8-14 being alkaline.
• Indicators like litmus paper and universal indicator change color depending on pH.
• Neutralization is a chemical reaction between an acid and alkali, resulting in a neutral solution (pH of 7).

Understanding these basic concepts of acids, alkalis, and neutralization provides a foundation for further exploration of chemical reactions and properties.