Welcome to Week 6 of Year 7 Chemistry! This week, we’ll explore acids, alkalis, and the pH scale. You’ll learn how to measure pH, what it means, and even create your own homemade pH indicator using materials from your kitchen.
Hour 1: What is pH?
Learning Objectives
By the end of this hour, you will:
Understand what pH measures.
Identify the difference between acids, alkalis, and neutral substances.
Create a pH indicator using natural materials.
Use your indicator to test the pH of household substances.
Introduction to pH and Homemade Indicators
The pH scale is a way of measuring how acidic or alkaline a substance is. It ranges from 0 to 14:
Acidic Substances: These have a pH less than 7. Examples include lemon juice, vinegar, and stomach acid.
Neutral Substances: These have a pH of exactly 7. Pure water is a great example.
Alkaline Substances (or Bases): These have a pH greater than 7. Examples include baking soda, soap, and bleach.
Alkalis are bases that are soluble in water.
Acids taste sour, while alkalis feel slippery. The pH of a substance can affect how it reacts with other materials, which is why it’s so important in chemistry!
Read and Watch
pHScale (MooMoo Maths and Science).
Task: Everyday pH
Look around your home and list three acidic and three alkaline substances you use daily.
Write down their pH ranges if you can find them (e.g., vinegar: pH 2-3).
Practical Activity: Red Cabbage pH Indicator
What You Need:
Red cabbage
A knife (with adult supervision) and chopping board
A pot and water
A strainer
Clear cups or jars
Various household substances to test (e.g., lemon juice, baking soda, vinegar, soap, water)
Steps:
Chop the red cabbage into small pieces.
Boil the cabbage pieces in a pot of water for about 10 minutes. The water will turn purple.
Strain the liquid into a clear container. This is your pH indicator.
Pour small amounts of the indicator into separate cups or jars.
Add a few drops of different household substances to each cup and observe the colour changes.
Reflection Questions:
What colours did you observe? (Hint: Acids turn the indicator reddish, neutral substances keep it purple, and alkalis turn it green or yellow.)
Which substances were most acidic or alkaline based on the colour change?
Hour 2: Exploring the Role of Acids and Alkalis
Learning Objectives
By the end of this hour, you will:
Understand how acids and alkalis are used in everyday life.
Learn about the importance of neutralization.
Read and Watch
Watch: Acids and Bases (MooMoo Maths and Science) for a visual explanation of acids, alkalis, and the pH scale.
Task: Real-Life Chemistry
Write a short paragraph about one-way acids or alkalis are used in daily life (e.g., cleaning, cooking, medicine).
Bonus: Research and write about neutralization, such as how antacids work to relieve heartburn.
Hour 3: Svante Arrhenius and Acid-Base Theory
Learning Objectives
By the end of this hour, you will:
Learn about Svante Arrhenius and his contributions to acid-base theory.
Understand how his discoveries shaped modern chemistry.
Read and Watch
Read: A biography of Svante Arrhenius from "Scientists and Inventors" page 234.
Key Concepts
Svante Arrhenius proposed that acids are substances that increase the concentration of hydrogen ions (H⁺) in water, while bases increase hydroxide ions (OH⁻).
This definition was groundbreaking and forms the basis of how we understand acids and bases today.
Task: Arrhenius in Action
Write a short paragraph summarising the Arrhenius definition of acids and bases.
Reflect: Why do you think this discovery was so important for science?
Quick Activity: Visualizing Hydrogen Ions
Draw a simple diagram showing how an acid (like HCl) releases hydrogen ions in water and how a base (like NaOH) releases hydroxide ions.
Summary and Reflection
Reflect on the Week:
What did you find most surprising about pH and how it’s measured?
How can understanding pH help us in everyday situations?
How did Svante Arrhenius’s work change our understanding of acids and bases?
Looking Ahead: Next week, we’ll investigate the states of matter. Get ready for experiments with solids, liquids, and gases—and learn how substances change between these states!
Congratulations on finishing week 6!
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