Chemistry in Water Chem Rxns in Aqueous Solns Solvent = Water Solute = acid, base or salt

IONIC COMPOUNDS Salt: constituent ions form solid crystal lattice, high MP, dissolves in H 2 O to give cations (+) and anions (-) surrounded by polar H 2 O molecules (Fig 11.1) Acid: produces H + in water, sour in taste –HBr  H + + Br - Base: produces OH - in water, bitter in taste –KOH  K + + OH -

ACIDS (1) Acids produce H + cations in an aqueous soln. Monoprotic acids give up to one H + ion per acid (*HCl-hydrochloric, *HNO 3 -nitric, HBr- hydrobromic) Diprotic acids give up to two H + ions per acid (*H 2 SO 4 -sulfuric). Triprotic (H 3 PO 4 -phosphoric). See uses of acids on pp , * You are using in lab

ACIDS (2) All acids on previously slide but phosphoric acid are strong acids meaning they ionize completely in water. –HBr  H + + Br - strong acid; every HBr ionizes. We say that the reaction is complete meaning essentially no reactant exists.

ACIDS (3) Weak acids do not ionize completely. –HF ↔ H + + F - weak acid –Only 1 per 100 HF ionizes. We say that HF and its constituent ions are in equilibrium meaning both reactants and products exist in balance. –Other weak acids: HNO 2 -nitrous, H 2 SO 3 - sulfurous, phosphoric, organic acids

Molarity (1) Concentration unit reflecting amount of solute in solvent Molarity = M = mole solute/liter soln Mole = number of 12 C atoms in exactly 12 g of 12 C = Avogadro’s number = 6.02E23 Let’s consider concentration of H + ions in water = [H + ]. 1 g H + = 1 mol H + Also 1 liter = 1 L = 1000 mL

Molarity (2) mol [H + ] in 1 L soln has a molarity of mol/1 L = M or 1E-3 M mol [H + ] in 0.1 L soln is 1E-5 5E-3 mol [H + ] in 1 L soln is 5E-3 M 2.34E-4 mol [H + ] in 1 L soln is 2.34E-4 M 4E-8 mol [H + ] in 0.5 L soln is 8E-8 M Ex 11.4: g H + in 0.50 L yields [H + ] = mol/0.50 L = 0.1 M

pH SCALE Another way to describe [H + ] is to use the pH scale where molarity is expressed as 1.0 x 10 -pH. Note that pH is the negative of the exponent meaning that pH is positive. –1E-3 M has pH = 3 –1E-5 has pH = 5 –5E-3 M = 1E-2.30 M has pH = 2.30 –2.34E-4 M = 1E-3.63 M has pH 3.63 –8E-8 M = 1E-7.10 M has pH = 7.10

pH SCALE (3) The pH scale goes from 1 to 14 corresponding to10 -1 M (very high [H + ]; pH = 1) to M (very low [H + ]; pH = 14). pH = 7 is a neutral solution pH < 7 means acidic Figure 11.9

BASES Bases produce OH - anions in an aqueous soln OH - anion is the hydroxide ion Strong bases ionize completely –LiOH  Li + + OH - Weak bases ionize to a small degree –Ca(OH) 2 ↔ Ca OH - –NH 3 + H 2 O ↔ NH OH - –CO H 2 O ↔ HCO OH - Uses on pp

pH and Bases If [H + ] > 1.0E-07 M or pH < 7, solution is acidic If [H + ] 7, solution is basic In an aqueous soln, [H + ] x [OH - ] = 1.0E-14 Pure Water has [H + ] = [OH - ] = 1.0E-07, is neutral and has a pH = 7 Figure 11.9

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ACID-BASE NEUTRALIZATION (1) H + + OH - ↔ H 2 O –An equilibrium is established –Neutralization  –Self ionization  Acid + Base  Salt + Water –HCl + NaOH  NaCl + H 2 O

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