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Chemistry in Water

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)

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Chemistry in Water

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

  2. 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 -

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 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-3.63M has pH 3.63 • 8E-8 M = 1E-7.10 M has pH = 7.10

  9. 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

  10. 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

  11. 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

  12. pH and Plants • pH Affects Nutrient, Minerals and Growth http://www.esf.edu/pubprog/brochure/soilph/soilph.htm Antacids

  13. ACID-BASE NEUTRALIZATION (1) • H+ + OH- ↔ H2O • An equilibrium is established • Neutralization  • Self ionization  • Acid + Base  Salt + Water • HCl + NaOH  NaCl + H2O

  14. 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 Balance http://www.e-kidneys.net/acidbase.html

  15. Gatorade • Development of Gatorade http://www.rgp.ufl.edu/publications/explore/v08n1/gatorade.html • Chemistry and Gatorade http://chemcases.com/gatorade/

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