# Acids, Bases and Salts

> CIE IGCSE Chemistry · CIE IGCSE Chemistry (0620)
> Source: https://www.owlsprep.com/study/cie-0620-u7-overview/
> Weight: 8-10% of combined MCQ and structured question sections

This unit covers core properties of acids, bases and salts, their reaction profiles, oxide classification, and standard laboratory salt preparation methods, a foundational inorganic chemistry topic.

**Prerequisites:** [Atomic Structure and Bonding](https://www.owlsprep.com/study/cie-0620-u2-atomic-structure-and-bonding/); [Chemical Formulae and Equations](https://www.owlsprep.com/study/cie-0620-u3-chemical-formulae-and-equations/)

## Learning objectives

- Describe characteristic properties of acids and bases, including reactions with metals, carbonates, and indicators
- Classify oxides as acidic, basic, amphoteric, or neutral and link classification to reaction behavior
- Select appropriate laboratory methods to prepare pure samples of soluble and insoluble salts
- Predict products of neutralization and common acid-base reaction pathways

## Unit at a glance

You will start by exploring the defining chemical and physical properties of acids and bases, including their effects on indicators, reaction rates, and product formation when reacted with common laboratory reagents.

You will then move to classifying different oxide types, before learning to select and carry out appropriate salt preparation methods, depending on whether the target salt is soluble or insoluble in water.

Work through the following sub-topics in order to master this unit:
- [Characteristic Properties of Acids and Bases](https://www.owlsprep.com/study/cie-0620-u7-characteristic-properties-of-acids-and/) — Covers the pH scale, indicator colour changes, and common reaction pathways for strong/weak acids and alkalis.
- [Oxides and Preparation of Salts](https://www.owlsprep.com/study/cie-0620-u7-oxides-and-preparation-of-salts/) — Explores oxide classification, solubility rules, and step-by-step methods to prepare pure dry salt samples in the lab.

## Common pitfalls

- **Wrong:** Assuming all metals react with acids to produce salt and hydrogen
  - Why it fails: Metals below hydrogen in the reactivity series (e.g. copper, silver) do not react with dilute acids
  - Correct: Cross-reference the reactivity series before predicting acid-metal reaction outcomes
- **Wrong:** Using the same preparation method for all salts
  - Why it fails: Soluble and insoluble salts require completely different synthetic pathways
  - Correct: First check salt solubility using standard rules to select the right preparation approach
- **Wrong:** Classifying all metal oxides as basic
  - Why it fails: Some metal oxides (e.g. aluminium oxide, zinc oxide) are amphoteric, reacting with both acids and bases
  - Correct: Memorize common amphoteric oxides and test for reactivity with both acidic and alkaline reagents

## Cheatsheet

| Concept/Formula | Description | Relevant Subtopic |
| --- | --- | --- |
| pH Scale | Acids have pH <7, neutral solutions pH=7, bases/alkalis pH >7 | Characteristic Properties of Acids and Bases |
| Neutralization General Reaction | Acid + Base → Salt + Water | Characteristic Properties of Acids and Bases |
| Acid + Carbonate General Reaction | Acid + Carbonate → Salt + Water + Carbon Dioxide | Characteristic Properties of Acids and Bases |
| Oxide Classification | Acidic (non-metal, reacts with bases), Basic (metal, reacts with acids), Amphoteric (reacts with both), Neutral (reacts with neither) | Oxides and Preparation of Salts |
| Insoluble Salt Preparation | Precipitation: mix two soluble salt solutions with desired ions, filter, wash, dry | Oxides and Preparation of Salts |
| Soluble Salt Preparation | Excess solid (metal/base/carbonate) + acid, filter, crystallize product | Oxides and Preparation of Salts |

## What's next

You are ready to start your first sub-topic on the characteristic properties of acids and bases, where you will learn to identify acids and bases using indicators and predict their reaction products. Once you complete both sub-topics in this unit, you will move on to the next unit covering chemical energetics.

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