GCSE Chemistry - Acids & Bases - pH | Features | Neutralisation Reactions (2026/27 exams)

The pH Scale00:00:31

The pH scale measures how acidic or alkaline a solution is, ranging from 0 to 14. Low numbers (0-6) indicate acidity, high numbers (8-14) indicate alkalinity, and 7 is neutral. Examples include stomach acid (pH 2) and bleach (pH 12).

Measuring pH: Indicators and Probes00:01:25

pH can be measured using chemical indicators, which are dyes that change color at different pH levels (e.g., universal indicator changes from red for acidic to blue/purple for alkaline). Alternatively, pH probes connected to a pH meter provide more accurate and precise numerical readings, removing human judgment.

Defining Acids and Bases00:02:47

Acids form aqueous solutions with a pH less than 7 by releasing hydrogen ions (H+) in water. Bases have a pH greater than 7. Alkalies are water-soluble bases that dissolve to form solutions with a pH greater than 7 and release hydroxide ions (OH-) in water.

Neutralization Reactions00:03:42

Neutralization reactions occur when an acid and a base react, typically producing a salt and water. For example, hydrochloric acid and sodium hydroxide react to form sodium chloride and water. This reaction can also be represented as hydrogen ions and hydroxide ions combining to form water, resulting in a neutral pH of 7.

Common Acids and Bases00:04:32

Common acids include hydrochloric acid, sulfuric acid, and nitric acid. Common bases are generally hydroxides or carbonates, such as sodium hydroxide and calcium carbonate. It is beneficial to remember these frequently encountered examples.