Acids, Bases, Salts and Reaction Rates
Core ideas
An acid releases H⁺ ions in water; a base neutralises an acid; an alkali is a soluble base releasing OH⁻ ions. The pH scale runs 0–14, with acids below 7 and alkalis above 7. Neutralisation: acid + base → salt + water. Acid + metal → salt + hydrogen; acid + carbonate → salt + water + carbon dioxide. Indicators show pH; titration determines concentration.
Reaction rate is the change in amount of reactant or product per unit time. Rate increases with higher temperature, higher concentration, greater surface area, and with a catalyst. Collision theory explains this: particles must collide with sufficient energy (activation energy) for reaction to occur.
Traps to watch
- pH is not linear in H⁺ concentration; it is a logarithmic scale.
- A catalyst does not change the yield or the position of equilibrium; it speeds up attainment of equilibrium.
- Surface area affects rate but not the total amount of product.
- Gas volume measurements must account for temperature and pressure.
Rule of thumb
For rate questions: more frequent or more energetic collisions = faster rate. For salts: choose the acid for the salt and the base for the cation.
Worked example
Name the salt formed by reacting sulfuric acid with copper(II) oxide. Sulfuric acid gives sulfate; copper(II) gives copper ion, so the salt is copper(II) sulfate; water is also formed.