Acids, bases, salts and reaction rates
Acids, bases, salts and reaction rates tests pH, neutralisation, salt preparation and the factors that change reaction speed.
Acids and bases
- Acids produce H+ ions in aqueous solution; bases neutralise acids; alkalis are soluble bases producing OH-.
- pH below 7 acidic, 7 neutral, above 7 alkaline. Universal indicator gives a colour match; litmus is less precise.
- Strong acids ionise completely; weak acids partially.
- Acid + metal -> salt + hydrogen. Acid + carbonate -> salt + water + carbon dioxide. Acid + base/alkali -> salt + water.
- Neutralisation ionic equation: H+ + OH- -> H2O.
Salt preparation
Soluble salts: acid + excess insoluble base/carbonate, filter excess, evaporate to crystallise. Titration for soluble salts from soluble bases. Insoluble salts by precipitation, e.g. barium sulfate from barium chloride and sodium sulfate.
Rates
Rate increases with higher concentration, higher temperature, larger surface area and a catalyst. Collision theory: more frequent and more energetic collisions. Catalyst lowers activation energy and is not used up. Rate graphs: steeper initial gradient = faster; same final amount if same limiting reactant.
Worked example
Prepare copper(II) sulfate: add excess copper(II) oxide to warm dilute sulfuric acid, stir, filter off excess black solid, evaporate filtrate to crystallisation point and cool. Equation: CuO + H2SO4 -> CuSO4 + H2O. The excess oxide ensures all acid is used.
Traps
Saying acid + carbonate gives hydrogen; forgetting excess solid must be filtered; thinking a catalyst is consumed; confusing rate with yield.