cm3 - Properties of acids Properties Taste Sour(kids...

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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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