Acids and Bases, Ionic Equations

Please - Potassium Stop - Sodium Complaining - Calcium My - Magnesium Aluminium - Aluminium Zipper - Zinc Is - Iron Too - Tin Loose. - Lead Help - Hydrogen Correct - Copper My - Mercury Spoiled - Silver Gown. - Gold

An acid is a substance that ionises/dissociates in water to form H+ ions. E.g. H2SO^4 (aq) → 2H+ (aq) + SO4^2− (aq) • Always simple covalent Hydrochloric acid: HCl, s, m Nitric acid: HNO3, s, m Sulfuric acid: H2SO4, s, d Phosphoric acid: H3SO4, w, t Ethanoic acid: CH3COOH, w, m Carbonic acid: H2CO3, w, d

Strength (Degree of dissociation/ionisation of acids & bases) - Strong acid/base: fully dissociates/ionises in water to produce lots of H+/OH- ions. - Weak acid/base: partially dissociates/ionises in water, some ions recombine and remain as molecules Concentration (Amount of solute in solution) - Concentrated acid (E.g. HCl): a lot of HCl dissolved in given vol. of H2O - Diulte acid (E.g. dilute HCl): little HCl dissolved in given vol. of H2O Basicity (Max. no. of H+ ions formed when a molecule of acid ionises in water) - Monobasic: Produce 1 H+ ion per molecule of the acid. (1:1) - Dibasic: Produce 2 H+ ions per molecule of the acid. (2:1) - Tribasic: Produce 3 H+ ions per molecule of the acid. (3:1)

• Acids dissolve and ionise in water (not organic solvents) to produce hydrogen ions • Hydrogen ions are responsible for acidic properties • Hence only exhibit acidic properties when they are dissolved in water

A base is a substance that reacts with an acid to form salt and water only. (neutralisation reaction). Generally, bases are metal oxides or hydroxides e.g. sodium oxide, barium hydroxide, etc. • Alkali: Soluble bases that ionise/dissociate in water to form hydroxide ions. • Salt: A salt is a substance that is formed when the hydrogen ion (H+) of an acid is replaced by a metal ion or an ammonium (NH4^+) ion. Sodium hydroxide: NaOH, s Potassium hydroxide: KOH, s Barium hydroxide: Ba(OH)2, s Aqueous ammonia: NH3, w, partially dissociate

Property 1: Acids + reactive metals -> salt + h2 Property 2: Acids + metal carbonates -> salt + co2 + h2o Property 3: Acids + metal oxides / hydroxides -> salt + h2o (neutralisation) - H+ (aq) + OH- (aq) -> H2O (l) Property 1: Alkalis + acids -> salt + h2o (neutralisation) - H+ (aq) + OH- (aq) -> H2O (l) Property 2: Alkalis + ammonium salts -> ∆ (heat is added) salt + h2o + nh3 gas.

Purpose: An ionic equation shows only the chemical species that are involved in a reaction, shows how ions present are reacting

Metallic oxides - Basic oxides react with acids to form salt and h2o; - ALL METALS, exceptions in amphoteric • Acidic oxides react with alkalis to form salt and h2o; • NON-METALS; s2, co2, p2o5 Non-metallic oxides - Amphoteric oxides react with both acids and alkalis to form salt; - Al2O3, PbO, ZnO (Aluminium, lead, zinc) • Neutral oxides do not react with either acids or alkalis; • GASES; co2, h2o, no

• acid <7, alkali >7; 0-14 1. 0-3 strong acid 2. 4-6 weak acid 3. 8-10 weak base 4. 11-14 strong base

• determines conc. of substances • start pt. & end pt. deduce strength of acid + alkali • check that end-pt lies in range of suitable indicator; SOME DON’T HAVE

• important control soil pH bc affects growth & development of plants • most plants grow best when pH neutral/slightly acidic • CANNOT grow if soil TOO ACIDIC when too much fertiliser added & leeches soil nutrients • also can be due to acid rain to remove, add: CALCIUM oxide (lime)/hydroxide (slaked lime)/carbonate - carbonate best: cheapest, will NOT make soil alkaline