Cambridge O Level Chemistry · Syllabus 5070 · Metals
Salt
What is Salt?
The compound formed when the hydrogen of an acid is replaced by a metal. When a metal above hydrogen in the reactivity series reacts with dilute hydrochloric acid the salt is a chloride, and hydrogen gas is released at the same time.
This definition is part of the Metals chapter in Cambridge O Level Chemistry.
Common mistakes with Salt
- 7. “Iron needs oxygen, water and salt to rust.” Repair The two required conditions are oxygen and water. Salt speeds rusting up but is not necessary — a nail rusts perfectly well in pure water and air. Listing salt as a condition is a common and expensive slip. Where Lesson 9.5A.
- 16. “Iron rusts when oxygen, water and salt are present.” Defect Promotes a rate factor to a required condition. Reason A nail in ordinary water and air rusts perfectly well, so salt cannot be necessary. Repair “Oxygen and water are required. Salt increases the rate.” Transfer Which tube in the four-tube experiment proves salt is not required? Tube A — it rusted without any.
Questions students ask about Salt
What conditions are needed for iron to rust?
Rusting needs both oxygen and water; if either is absent, rust does not form. Salt speeds up rusting but is not a required condition — a nail rusts perfectly well in pure water and air. The product is hydrated iron(III) oxide, and the full name must include both the oxidation state and the water of hydration.
Reviewed by Academiq Edu Instructor PanelLast reviewed Syllabus 2026-2028