AP Chapter 14 - Arrhenius Definition Acids produce hydrogen...

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1 Arrhenius Definition s 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 NH 3 ammonia could not be an Arrhenius base. Bronsted-Lowry Definitions s And acid is an 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 HCl(g) + H 2 O(l) H 3 O + + Cl - s Water is a base -makes hydronium ion Pairs s General equation s HA(aq) + H 2 O(l) H 3 O + (aq) + A - (aq) s Acid + Base Conjugate acid + Conjugate base s This is an equilibrium. s Competition for H + between H 2 O and A - s The stronger base controls direction. s If H 2 O is a stronger base it takes the H + s Equilibrium moves to right. Acid dissociation constant K a s The equilibrium constant for the general equation. s HA(aq) + H 2 O(l) H 3 O + (aq) + A - (aq) s K a = [H 3 O + ][A - ] [HA] s H 3 O + is often written H + ignoring the water in equation (it is implied). Acid dissociation constant K a s HA(aq) H + (aq) + A - (aq) s K a = [H + ][A - ] [HA] s We can write the expression for any acid. s Strong acids dissociate completely. s Equilibrium far to right. s Conjugate base must be weak.
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2 Back to Pairs s Strong acids s K a is large s [H + ] is equal to [HA] s A - is a weaker base than water s Weak acids s K a is small s [H + ] <<< [HA] s A - is a stronger base than water Types of Acids s Polyprotic Acids- more than 1 acidic hydrogen (diprotic, triprotic). s Oxyacids - Proton is attached to the oxygen of an ion. s Organic acids contain the Carboxyl group -COOH with the H attached to O s Generally very weak. Amphoteric s Behave as both an acid and a base. s Water autoionizes s 2H 2 O(l) H 3 O + (aq) + OH - (aq) s K W = [H 3 O + ][OH - ]=[H + ][OH - ] s At 25ºC K W = 1.0 x10 -14 s In EVERY aqueous solution. s Neutral solution [H + ] = [OH - ]= 1.0 x10 -7 s Acidic solution [H + ] > [OH - ] s Basic solution [H + ] < [OH - ] pH s pH= -log[H + ] s Used because [H + ] is usually very small s As pH decreases, [H + ] increases exponentially s Sig figs only the digits after the decimal
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AP Chapter 14 - Arrhenius Definition Acids produce hydrogen...

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