Deep Dive: What Actually Makes an Acid?
Part of Acids and Alkalis — GCSE Chemistry
This deep dive covers Deep Dive: What Actually Makes an Acid? within Acids and Alkalis for GCSE Chemistry. Revise Acids and Alkalis in Chemical Changes for GCSE Chemistry with 20 exam-style questions and 20 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 2 of 12 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 2 of 12
Practice
20 questions
Recall
20 flashcards
🔬 Deep Dive: What Actually Makes an Acid?
When an acid dissolves in water, it releases hydrogen ions (H⁺) into the solution. These tiny, positively charged particles are what make acids behave the way they do — they are responsible for the sour taste of citric acid, the corrosive nature of concentrated acids, and the reactions with metals and carbonates. The more H⁺ ions in a solution, the more acidic it is and the lower the pH.
Think of an acid as a "hydrogen ion donor". When you dissolve it in water, it breaks apart and releases H⁺. The water molecules play an essential role — without water, acids cannot fully ionise or show their acidic properties. That is why pure (anhydrous) acids are far less reactive than their aqueous solutions.
The key equations:
Hydrochloric acid: HCl → H⁺ + Cl⁻
Sulfuric acid: H₂SO₄ → 2H⁺ + SO₄²⁻
Nitric acid: HNO₃ → H⁺ + NO₃⁻
Alkalis are the opposite: they release hydroxide ions (OH⁻) when dissolved in water.
Sodium hydroxide: NaOH → Na⁺ + OH⁻
Potassium hydroxide: KOH → K⁺ + OH⁻
Remember: An alkali is a base that dissolves in water. All alkalis are bases, but not all bases are alkalis (e.g., copper oxide is a base but doesn't dissolve).