# Acidic and basic oxides

> Why an acid can dissolve rust


## Objectives

- State that most metal oxides are basic oxides: they react with acids to give a salt and water.
- State that most non-metal oxides are acidic oxides: they dissolve in water to give acids.
- Classify an oxide as basic or acidic from its element.

## 1. Acidic and basic oxides: from zero




## 2. Acid vs rust

Predict: will rust fizz and give hydrogen gas in the acid, like iron metal?

- No, it dissolves without giving a gas ✓
- No, nothing happens to rust in an acid
- Yes, it fizzes, because rust contains iron

Rust dissolves in the acid without giving off hydrogen gas. Rust is an iron oxide, not free iron metal: the acid's hydrogen combines with the oxide's oxygen to form water, and a salt forms with it.

[ar-EG] الـ rust بيدوب في الـ acid من غير ما يطلّع hydrogen gas. عشان الـ rust ده iron oxide، مش iron metal حر: الـ hydrogen بتاع الـ acid بيتحد مع الـ oxygen اللي في الـ oxide ويكوّن مية، ومعاها بيتكوّن salt.
## 3. Basic oxides

Basic oxide A metal oxide that reacts with an acid to give a salt and water. copper (II) oxide + sulphuric acid → copper (II) sulphate + water A basic oxide acts like a base. So it neutralizes the acid: salt and water, no gas.


## 4. Acidic oxides

Acidic oxide A non-metal oxide that dissolves in water to give an acid. sulphur trioxide + water → sulphuric acid Basic oxides Most metal oxides: $Na_2O$, MgO, CuO Acidic oxides Most non-metal oxides: $CO_2$, $SO_3$ Say **most**. A few metal oxides, such as $Al_2O_3$, react with acids and with bases too.


## 5. Classify and predict

Basic oxide or acidic oxide? A basic oxide reacts with an acid to give a salt and ___.


## 6. Summary

Most metal oxides are basic oxides: basic oxide + acid → salt + water. Most non-metal oxides are acidic oxides: they dissolve in water to give acids. Rust is an iron oxide, a basic oxide, so an acid dissolves it. Key words: **basic oxide**, **acidic oxide**, **salt and water**. Can you explain why an acid dissolves copper (II) oxide but gives no hydrogen gas? copper (II) oxide + sulphuric acid → copper (II) sulphate + water Copper (II) oxide is a basic oxide, not free metal: it neutralizes the acid to give a salt and water. The acid's H joins the oxide's O to form water, so no gas is given off.



Chapter: Transition Elements (https://yaani.ai/en/learn/chemistry/chem-s3-en.ch1)
Source: https://yaani.ai/en/lesson/chem-s3-en.lesson-chem.oxides