Acids, Bases and pH
Acids and bases are chemical opposites found in everyday life. The pH scale measures how acidic or basic a substance is. Understanding acids and bases is fundamental to chemistry and biology.
What You Need to Know
Key Concept Diagram
The pH scale runs from 0 to 14: acids are below 7, neutral is 7, bases are above 7
Acids donate hydrogen ions (H+); bases accept hydrogen ions or donate hydroxide ions (OH-)
Neutralisation: acid + base reaction produces salt and water
Indicators (litmus, universal indicator) change colour to show whether a substance is acidic or basic
Key Vocabulary
pH scale
A scale from 0 to 14 measuring acidity (0-6), neutrality (7), and alkalinity (8-14)
Acid
A substance that releases hydrogen ions (H+) in water; pH below 7
Base (Alkali)
A substance that accepts hydrogen ions or releases hydroxide ions; pH above 7
Neutralisation
The reaction between an acid and a base to produce salt and water
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
A substance has a pH of 3. It is:
Question 2
What is produced when an acid and a base react?
Question 3
Universal indicator is added to a colourless liquid, which turns green. The liquid is:
Key Concepts Summary
- ●The pH scale runs from 0 to 14: acids are below 7, neutral is 7, bases are above 7
- ●Acids donate hydrogen ions (H+); bases accept hydrogen ions or donate hydroxide ions (OH-)
- ●Neutralisation: acid + base reaction produces salt and water
- ●Indicators (litmus, universal indicator) change colour to show whether a substance is acidic or basic