NYGH Acids, Bases and Salts Notes

1 Chem!stry Name: …………………… ( ) Class: ……………… Date: …… / …… / …… Essential Notes: Acids, Bases and Salts Names and Formulae of Some Common Acids, Bases and Salts: • Acids: Examples include: hydrochloric acid – HCl, nitric acid – HNO3, sulfuric acid – H2SO4, phosphoric acid – H3PO4, ethanoic acid – CH3COOH • Bases / Alkalis: Note: The term alkali is used to describe a base that is soluble in water, and has been dissolved in water so that it can be used as a solution. Not all bases are soluble in water, and so not all bases are alkalis. Examples include: copper(II) oxide – CuO, sodium hydroxide – NaOH, calcium hydroxide – Ca(OH)2, ammonia – NH3. • Salts: Examples include: sodium chloride – NaCl, copper(II) sulphate – CuSO4, ammonium nitrate – NH4NO3 Definitions: • Acid: An acid is a chemical that dissolves in water to produce hydrogen ions, H+(aq), as the only positive ion: HCl(g) → H+(aq) + Cl–(aq) HNO3(l) → H+(aq) + NO3–(aq) H2SO4(l) → 2H+(aq) + SO42–(aq) Note: Sulfuric acid is said to be dibasic because 1 mol of the acid produces 2 mol of hydrogen ions (also, H2SO4 can donate 2 mol of H+ or 2 mol of H+ can be replaced by a metal to form a salt). The hydrogen ions that are produced do not exist on their own, but bond to water molecules to form hydroxonium ions, H3O+(aq): H+(aq) + H2O(l) → H3O+(aq) Therefore, the complete balanced chemical equation for an acid dissolving in water should be written: HNO3(l) + H2O(l) → H3O+(aq) + NO3 –(aq) (a monobasic acid) CH3COOH(l) + H2O(l) ∏ H3O+(aq) + CH3COO–(aq) (a monobasic acid) H2SO4(l) + 2H2O(l) → 2H3O+(aq) + SO42–(aq) (a dibasic acid) H3PO4(l) + 3H2O(l) → 3H3O+(aq) + PO43–(aq) (a tribasic acid)

2 The dot and cross diagram of the hydroxonium ion is given below: Note: The hydrogen that originated from the acid (shown on the left) is sharing two electrons (two dots) which both belong to the oxygen. This special type of covalent bond is known as a dative covalent bond. An important fact to arise from this is that an acidic chemical will only exhibit its acidic properties when dissolved in water. Therefore, when writing balanced chemical equations, all acids must be in an aqueous state, (aq). • Base / Alkali: Bases tend to be metal oxides and metal hydroxides. Ammonia, NH3, is also basic. As opposed to producing hydrogen ions, which is the property of an acid, a base will accept hydrogen ions to form water as one of the products: CuO(s) + 2H+(aq) → Cu2+(aq) + H2O(l) NaOH(s) + H+(aq) → Na+(aq) + H2O(l) A base which is soluble in water is described as an alkali. Examples of alkalis include sodium hydroxide, NaOH, and ammonia, NH3. Alkalis tend to dissolve in water to produce hydroxide ions, OH –(aq): NaOH(s) → Na+(aq) + OH–(aq) NH3(g) + H2O(l) → NH4+(aq) + OH–(aq) Hydroxide ions (from alkalis) react with hydrogen ions (from acids) to form water. This