Acid Ionisation and Strength

All acids ionise when dissolved in water, but here's the key point: acid strength is completely different from acid concentration. Don't get these mixed up in your exams!

Strong acids fully ionise in water, meaning every acid molecule breaks apart to release H+ ions. Weak acids only partially ionise - just some of their molecules split up.

Remember: You can have a concentrated weak acid or a dilute strong acid - strength and concentration are totally separate concepts!

Most acids you encounter are actually weak acids, like ethanoic acid in vinegar (CH₃COOH).

Weak Acids in Detail

Weak acids are everywhere in chemistry, and most acids fall into this category. They only partially ionise, so not all molecules release H+ ions when dissolved.

Take ethanoic acid - the main ingredient in vinegar. Its chemical formula is CH₃COOH, and when it ionises: CH₃COOH ⇌ CH₃COO⁻ + H+.

Quick Tip: Notice the reversible arrow (⇌) - this shows that only some molecules ionise whilst others remain whole!

This partial ionisation is why weak acids are generally safer to handle than strong acids.

Electrolysis Basics

Electrolysis uses electricity to break down ionic compounds - but only when they're dissolved in water or molten. You need a direct current (DC) power source to make it work.

At the positive electrode (anode), you'll get chlorine, bromine, or iodine if they're present - otherwise oxygen from water. At the negative electrode (cathode), you get metals that are less reactive than hydrogen (like copper) - otherwise hydrogen gas.

Memory Aid: Think "PANIC" - Positive Anode, Negative Is Cathode!

Key reactions include: 2Cl⁻ → Cl₂ + 2e⁻ and Cu²⁺ + 2e⁻ → Cu.

Making Pure, Dry Salts

Making copper sulfate crystals is a classic practical you'll likely do. Mix copper oxide with sulfuric acid, then heat until half the water evaporates.

The pH scale is essential knowledge: acids are pH 1-6, neutral is pH 7, and alkalis are pH 8-14. Remember this for your exams!

Practical Tip: Always leave your solution to crystallise slowly - rushing this step gives you smaller, less pure crystals!

The key is controlling evaporation carefully to get those perfect blue crystals.

Reactivity Series and Salt Formation

The reactivity series runs from potassium (most reactive) down to gold (least reactive). You absolutely must memorise this order: K, Na, Li, Ca, Mg, C, Zn, Fe, H, Cu, Au.

Making salts involves neutralisation reactions. The main patterns are:

• Metal + acid → salt + hydrogen
• Metal oxide/hydroxide + acid → salt + water
• Metal carbonate + acid → salt + water + CO₂

Exam Success: These reaction patterns come up constantly - learn them inside out!

Strong acids fully ionise, which is why they're called "strong" - it's all about complete ionisation.

Displacement and Metal Properties

Displacement reactions happen when more reactive metals push out less reactive ones. Metals react with water to produce metal hydroxides and hydrogen gas (watch for fizzing and floating).

When metals react with chlorine, you get metal chlorides - look for grey metals burning with green-yellow flames to form white solids. Ions are simply charged atoms.

Key Insight: In alloys, distorted layers can't slide past each other - that's why alloys are stronger than pure metals!

Group 7 elements form diatomic molecules like Cl₂. In graphite, each carbon has delocalised electrons allowing conductivity.

Acid-Carbonate Reactions

Here's a classic reaction you'll see everywhere: hydrochloric acid + calcium carbonate → calcium chloride + water + carbon dioxide. This follows the standard pattern perfectly.

The general rule is simple: acid + carbonate → salt + water + carbon dioxide. Every single time, without fail.

Exam Pointer: This reaction type appears in multiple choice questions constantly - nail the pattern now!

Watch for the fizzing when CO₂ gas is produced - it's a dead giveaway that carbonates are involved.

Acid-Hydroxide Reactions

Neutralisation reactions are beautifully simple. Take hydrochloric acid + sodium hydroxide → sodium chloride + water. Clean and straightforward!

The pattern is always: acid + metal hydroxide → salt + water. No gases produced, just salt and water every time.

Remember: Metal hydroxides are bases - they neutralise acids completely in these reactions!

This is probably the most important reaction type in acid chemistry.

Bonding and Properties

Metals are strong, dense, and excellent conductors with high melting points. Non-metals are often brittle insulators with lower density - completely opposite properties.

Ionic bonding happens when electrons transfer completely. Magnesium gives electrons to oxygen: Mg → Mg²⁺ and O → O²⁻, forming giant ionic lattices.

Key Concept: Electrostatic forces between oppositely charged ions act in all directions, creating high melting and boiling points!

These strong bonds throughout the lattice structure explain why ionic compounds are so stable.

Gas Tests and Reactions

Testing for hydrogen: use a lighted splint - hydrogen makes a distinctive squeaky pop sound. Testing for carbon dioxide: bubble it through limewater, which turns cloudy white.

The key acid reactions with metals and carbonates follow predictable patterns you've seen before. Sodium carbonate + hydrochloric acid gives sodium chloride, CO₂, and water.

Practical Success: Master these gas tests - they're guaranteed to appear in your practicals and exams!

These simple tests can identify gases instantly and are essential practical skills.