Presentation on theme: "Properties of acids n Taste Sour (kids, dont try this at home). n Conduct electricity. n Some are strong, some are weak electrolytes. n React with metals."— Presentation transcript:
Properties of acids n Taste Sour (kids, dont try this at home). n Conduct electricity. n Some are strong, some are weak electrolytes. n React with metals to form hydrogen gas. n Change indicators (litmus red). n React with hydroxides to form water and a salt.
Properties of bases n React with acids to form water and a salt. n Taste bitter. n Feel slippery (Dont try this either). n Can be strong or weak electrolytes. n Change indicators (litmus blue).
Types of Acids and Bases Several Definitions
Arrhenius Definition n Acids produce hydrogen ions in aqueous solution. n Bases produce hydroxide ions when dissolved in water. n Limits to aqueous solutions. n Only one kind of base. n NH 3 ammonia could not be an Arrhenius base.
Polyprotic Acids n Some compounds have more than 1 ionizable hydrogen. n HNO 3 nitric acid - monoprotic n H 2 SO 4 sulfuric acid - diprotic - 2 H + n H 3 PO 4 phosphoric acid - triprotic - 3 H +
Bronsted-Lowry Definitions n An acid is a proton (H + ) donor and a base is a proton acceptor. n Acids and bases always come in pairs. n HCl is an acid. n When it dissolves in water it gives its proton to water. n HCl(g) + H 2 O(l) H 3 O + + Cl - n Water is a base -makes hydronium ion.
Come in Pairs n General equation n HA(aq) + H 2 O(l) H 3 O + (aq) + A - (aq) n Acid + Base Conjugate acid + Conjugate base n This is an equilibrium. n B(aq) + H 2 O(l) BH + (aq) + OH - (aq) n Base + Acid Conjugate acid + Conjugate base n NH 3 (aq)+H 2 O(l) NH 4 + (aq)+OH - (aq)
Water n Water ionizes- falls apart into ions. H 2 O H + + OH - H 2 O H + + OH - n Called the self ionization of water. n Only a small amount. n [H + ] = [OH - ] = 1 x M n A neutral solution. n In water Kw = [H + ] x [OH - ] = 1 x n Kw is called the ion product constant.
Ion Product Constant H 2 O H + + OH - H 2 O H + + OH - n Kw is constant in every aqueous. solution [H + ] x [OH - ] = 1 x M 2 n If [H + ] > then [OH - ] then [OH - ] < n If [H + ] n If we know one, we can determine the other. n If [H + ] > acidic [OH - ] acidic [OH - ] < n If [H + ] 10 -7
Logarithms n Powers of ten. n A shorthand for big, or small numbers. n pH = -log[H + ] n in neutral pH = - log(1 x ) = 7 n in acidic solution [H + ] > n pH < -log(10 -7 ) n pH < 7 n in base pH > 7
pH and pOH n pOH = - log [OH - ] n [H + ] x [OH - ] = 1 x M 2 n pH+pOH = 14
Strength n Strong acids and bases are strong electrolytes n They fall apart completely. n Weak acids dont completely ionize. n Concentrated- much dissolved. n Strong forms many ions when dissolved. n Mg(OH) 2 is a strong base- it falls completely apart when dissolved. n Not much dissolves.
Measuring strength n Ionization is reversible. n HAH + + A - n makes an equilibrium. n Equilibrium constant for an acid(acid dissociation constant.) n K a = [H + ][A - ] [HA] n Stronger acid- more products. n larger K a (pg 450)
What about bases? n Strong bases dissociate completely. n B + H 2 O BH + + OH - n Base dissociation constant. n K b = [BH + ][OH - ] [B] n We can ignore the water because its concentration doesnt change. n Stronger base more dissociated. n Larger K b.
Practice n Write the expression for HNO 2 n Write the K b for NH 3
Neutralization Reactions Acid + Base Salt + water Acid + Base Salt + water n Salt = an ionic compound n Water = HOH HNO 3 + KOH HNO 3 + KOH HCl + Mg(OH) 2 HCl + Mg(OH) 2 H 2 SO 4 + NaOH H 2 SO 4 + NaOH n Really just double replacement.
Reactions Happen in Moles n How many moles of HNO 3 are need to neutralize 0.86 moles of KOH? n How many moles of HCl are needed to neutralize 3.5 moles of Mg(OH) 2 ?
Usually happen in solutions n 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? n If it takes 58 mL of an H 2 SO 4 solution to neutralize 0.34 moles of NaOH what is the concentration of the H 2 SO 4 solution?
Titration Determining an unknown
Titration n When you add the same number of moles of acid and base, the solution is neutral. n By measuring the amount of a base added you can determine the concentration of the acid. n If you know the concentration of the base. n This is a titration.
Titration equations n M a x V a x # of H + = M b x V b x # of OH - n really moles of H + = moles of OH -
More Practice n 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 ? n If it takes 67 mL of M H 2 SO 4 to neutralize 15mL of Al(OH) 3 what was the concentration of the Al(OH) 3 ? n How much of a M HCl will be needed to neutralize 25mL of.154 M NaOH?
Solubility n Dissolving stuff is an equilibrium n CaCl 2 (s) Ca +2 (aq) + 2 Cl - (aq) n You can write and equilibrium constant for dissolving n K eq = [Ca +2 ] [Cl - ] 2 [CaCl 2 ] n The concentration of a solid does not change, so we can combine it with K eq n K sp = [Ca +2 ] [Cl - ] 2
Solubility n K sp is called the solubility product constant n The more soluble a solid is the greater K sp n Used for slightly soluble salts. n Can tell if a precipitate will form. n Do the math n If the answer is bigger than the Ksp it will form n If not, it will all stay dissolved