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Unformatted text preview: Properties of acids Properties
Taste Sour (kids, don’t try this at home). s Conduct electricity. s Some are strong, some are weak electrolytes. s React with metals to form hydrogen gas. s Change indicators (litmus red). s React with hydroxides to form water and a salt.
s Properties of bases Properties
React with acids to form water and a salt. s Taste bitter. s Feel slippery (Don’t try this either). s Can be strong or weak electrolytes. s Change indicators (litmus blue).
s Types of Acids and Bases Types
Several Definitions Arrhenius Definition Arrhenius
Acids produce hydrogen ions in aqueous solution. s Bases produce hydroxide ions when dissolved in water. s Limits to aqueous solutions. s Only one kind of base.
s s NH3 ammonia could not be an Arrhenius base. Polyprotic Acids Polyprotic
s Some compounds have more than 1 ionizable hydrogen. HNO3 nitric acid monoprotic H2SO4 sulfuric acid diprotic 2 H+ H3PO4 phosphoric acid triprotic 3 H+ s s s Bronsted-Lowry Definitions Bronsted-Lowry
An acid is a proton (H+) donor and a base is a proton acceptor. s Acids and bases always come in pairs. s HCl is an acid. s When it dissolves in water it gives its proton to water.
s s s HCl(g) + H2O(l) H3O+ + Cl Water is a base makes hydronium ion. Come in Pairs Come
s s s General equation HA(aq) + H2O(l) H3O+(aq) + A(aq) Acid + Base Conjugate acid + Conjugate base s This is an equilibrium.
s s B(aq) + H2O(l) Base + Acid BH+(aq) + OH(aq) Conjugate acid + Conjugate base s NH (aq)+H O(l) NH +(aq)+OH(aq) Water Water
s s s Water ionizes falls apart into ions. H2O → H+ + OH Called the self ionization of water. s Only a small amount. [H+ ] = [OH] = 1 x 107M s A neutral solution.
s In water Kw = [H+ ] x [OH] = 1 x 1014 s Kw is called the ion product constant.
s Ion Product Constant Ion
s s H2O H+ + OH H Kw is constant in every aqueous. solution [H+] x [OH] = 1 x 1014M2 If [H+] > 107 then [OH] < 107 s s If [H+] < 107 then [OH] > 107 s If we know one, we can determine the other. s If [H+] > 107 acidic [OH] < 107 s If [H+] < 107 basic [OH] > 107 Logarithms Logarithms
Powers of ten. s A shorthand for big, or small numbers.
s s s s s pH = log[H+] in neutral pH = log(1 x 107) = 7 in acidic solution [H+] > 107 pH < log(107) s pH < 7 s in base pH > 7 pH and pOH pH
s s pOH = log [OH] [H+] x [OH] = 1 x 1014M2 s pH+pOH = 14 [H+] 10 10 01 0 1 Acidic 14 13 10 10 10 10 10 pH 9 11 3 5 7 3 11 79 Neutral 9 75 5 11 3 10 10 13 14 13 14 Basic 1 0 1014 1013 1011 pOH 109Basic 105 103 101 100 107 [OH] How Strong How Strength Strength
Strong acids and bases are strong electrolytes s They fall apart completely. s Weak acids don’t completely ionize. s Concentrated much dissolved. s Strong forms many ions when dissolved. s Mg(OH) is a strong base it falls completely 2 apart when dissolved. s Not much dissolves.
s s s Ionization is reversible. Measuring strength Measuring HA H+ + A s makes an equilibrium. s Equilibrium constant for an acid(acid dissociation constant.) Ka = [H+ ][A ] [HA] s Stronger acid more products.
s s larger Ka (pg 450) What about bases? What
s s s Strong bases dissociate completely. B + H2O BH+ + OH Base dissociation constant. s K = [BH+ ][OH] b [B] s We can ignore the water because it’s concentration doesn’t change. s Stronger base more dissociated. s Larger K b. Practice Practice
s s Write the expression for HNO2 Write the Kb for NH3 Neutralization reactions Neutralization Neutralization Reactions
s Acid + Base → Salt + water s Salt = an ionic compound s Water = HOH s HNO + KOH → 3 s HCl + Mg(OH) → 2 sH
2 SO4 + NaOH → s Really just double replacement. Reactions Happen in Moles
s How many moles of HNO are need to 3 neutralize 0.86 moles of KOH? s How many moles of HCl are needed to neutralize 3.5 moles of Mg(OH)2 ? Usually happen in solutions Usually
s If it takes 87 mL of an HCl solution to neutralize 0.67 moles of Mg(OH)2 what is the concentration of the HCl solution?
s If it takes 58 mL of an H SO4 solution to neutralize 0.34 moles of NaOH what is the concentration of the H2SO4 solution?
2 Titration Titration
Determining an unknown Titration Titration
When you add the same number of moles of acid and base, the solution is neutral. s By measuring the amount of a base added you can determine the concentration of the acid. s If you know the concentration of the base. s This is a titration.
s Titration equations Titration
s s Ma x Va x # of H+ = Mb x Vb x # of OH really moles of H+= moles of OH More Practice More
s If it takes 45 mL of a 1.0 M NaOH solution to neutralize 57 mL of HCl, what is the concentration of the HCl ? If it takes 67 mL of 0.500 M H2SO4 to neutralize 15mL of Al(OH)3 what was the concentration of the Al(OH)3 ? s s How much of a 0.275 M HCl will be needed to neutralize 25mL of .154 M NaOH? Solubility Solubility
Dissolving stuff is an equilibrium s CaCl2(s) Ca+2 (aq) + 2 Cl (aq) s You can write and equilibrium constant for dissolving s K = [Ca+2] [Cl]2 eq [CaCl2] s The concentration of a solid does not change, so we can combine it with Keq
s s Ksp = [Ca+2] [Cl]2 Solubility Solubility
s s s Ksp is called the solubility product constant The more soluble a solid is the greater Ksp Used for slightly soluble salts. s Can tell if a precipitate will form. s Do the math s If the answer is bigger than the Ksp it will form s If not, it will all stay dissolved ...
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This document was uploaded on 02/06/2011.
- Spring '08