Chapter 20: Acids, Bases, and pH Flashcards
what do acids do?
dissociate from H+ ions in aqueous solution
what do alkaline do?
dissociate OH- ions in aqueous solution
what is a Bronsted-Lowry acid
proton (H+) donor
what is a Bronsted-Lowry base
proton )H+) acceptor
what is a conjugate acid-base pair
two chemical species that can be interconverted
In a conjugate acid-base pair which is the conjugate base and the conjugate acid
conjugate base is the species that accepts the H+
conjugate acid is the species that accepts the H+
what does dissociation in aqueous solution require
presence of water
what is H3O+ (three possible names)
hydronoium ion
oxonium ion
hydroxonium ion
what does amphoteric mean and give an example of an amphoteric species
can act as an acid and a base depending on what it reacts with
example is water
what happens when strong acids react with weak acids and why
stronger acids donate H+ because they fully dissociate
what does monoprotic/monobasic mean
the substance can donate/accept one H+ per molecule
how would you reference a substance that can donate/accept more than one proton per molecule
diprotic/dibasic for two
triprotic/tribasic for three
what is pH
measurement of concentration of H+ in solution
give an overview of each pH
pH<7
pH=7
pH>7
pH<7 increasingly acidic
pH=7 neutral
pH>7 increasingly basic/alkaline
what is the pH equation
pH = -log[H+]
what is the rearranged pH equation to give [H+]
[H+] = 10^-pH
give the four general acid reaction word equations
acid + metal –> salt + hydrogen
acid + carbonate –> salt + water + carbon dioxide
acid + base –> salt + water
acid + alkali –> salt + water
what do weak acids do
partially dissociate
what is the special equilibrium for weak acids
acid dissociation constant Ka
what is the general equation for weak acids
HA(aq) H+(aq) + A-(aq)
what is the Ka equation
Ka = ( [H+] x [A-] ) / [HA]
what can cause Ka to change (if reaction uses same reactants)
the value can only change due to changes in temperature
what does the Ka value tell you
greater the value of Ka the further to the right the equilibrium is
the lower the value the further to the left the equilibrium is
what is the problem with Ka and what is the solution
value can be extremely big or small so use pKa instead
what is pKa and the pKa equation
log function of Ka
pKa = -logKa
what are the two approximations for simplifying Ka
1 [H+] = [A-]
2 [HA]eqm = [HA]start
what is the simplified Ka equation after the approximation are made
Ka = [H+]^2 / [HA]start
what are the problems with each approximation
1 If [H+] becomes siginificant [H=] cant equal [A-] so breaks down for very weak acids (pH>6) or dilute solutions
2 assumes negligible dissociation of acid which is not possible for dilute solutions or far stronger weak acids
what is the special equilibrium for water
ionic product of water
Kw
what is the general Kw equation
Kw = [H+] x [OH-]
when is Kw constant and what is its value at this point
constant @ 298K (25C)
Kw = 1 x 10^-14
Use ratio of [H+] : [OH-] to define acidic, neutral and alkaline
acidic [H+] > [OH-]
neutral [H+] = [OH-]
alkaline [H+] < [OH-]
