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 H2O to give cations (+) and anions (-) surrounded by polar H2O 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, *HNO3-nitric, HBr-hydrobromic)

• Diprotic acids give up to two H+ ions per acid (*H2SO4-sulfuric).

• Triprotic (H3PO4-phosphoric).• See uses of acids on pp 420-421, 424-25• * 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: HNO2-nitrous, H2SO3-sulfurous, phosphoric, organic acids

Molarity (1)

• Concentration unit reflecting amount of solute in solvent

• Molarity = M = mole solute/liter soln• Mole = number of 12C atoms in exactly 12 g

of 12C = 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)

• 0.001 mol [H+] in 1 L soln has a molarity of 0.001 mol/1 L = 0.001 M or 1E-3 M.

• 0.000001 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: 0.050 g H+ in 0.50 L yields [H+] = 0.050 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 10-14 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 ↔ Ca2+ + 2OH-

– NH3 + H2O ↔ NH4+ + OH-

– CO32- + H2O ↔ HCO3

- + OH-

• Uses on pp 428-430

pH and Bases

• If [H+] > 1.0E-07 M or pH < 7, solution is acidic

• If [H+] < 1.0E-07 M or pH >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

pH and Plants

• pH Affects Nutrient, Minerals and Growth

http://www.esf.edu/pubprog/brochure/soilph/soilph.htm

Antacids

ACID-BASE NEUTRALIZATION (1)

• H+ + OH- ↔ H2O

– An equilibrium is established– Neutralization – Self ionization

• Acid + Base Salt + Water– HCl + NaOH NaCl + H2O

Hyponatremia

• Duluth News-Tribune• The Pittsburgh Channel Feb 4, 2005 • Water of Life, Water of Death

http://www.mashinc.org/resources-essay-water.html

• Acid-Base Balancehttp://www.e-kidneys.net/acidbase.html

Gatorade

• Development of Gatorade http://www.rgp.ufl.edu/publications/explore/v08n1/gatorade.html

• Chemistry and Gatorade http://chemcases.com/gatorade/