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, HBrhydrobromic)
• 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.
–
 H+ + Br - strong acid; every HBr
ionizes. We say that the reaction is complete
meaning essentially no reactant exists.
HBr
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, H2SO3sulfurous, 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
 Li+ + OH• Weak bases ionize to a small degree
– Ca(OH)2 ↔
–
LiOH
Ca2+ + 2OH-
– NH3 + H2O ↔
– CO32- + H2O ↔
NH4+ + OH-
• Uses on pp 428-430
HCO3- + OH-
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-essaywater.html
• Acid-Base Balance
http://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/