AP Acids and Bases Concepts Flashcards
What is the Arrenhius definition of an acid?
an Arrenhius acid has an H+
What is the Arrenhius definition of a base?
an Arrenhius base has an OH-
What is the Bronsted-Lowry (BL) definition of an acid?
a BL acid donates a proton (H+)
What is the Bronsted-Lowry (BL) definition of a base?
a BL base accepts a proton (H+)
What is an amphoteric compound? What is an example of an amphoteric compound?
a compound that can act as an acid or a base; water
What will a BL acid always produce in water?
hydronium (H3O+)
What will a BL base always produce in water?
hydroxide (OH-)
What are Ka and Kb?
dissociation constants for acids (a) and bases (b)
If K > 1, reaction shifts
right (more products than reactants)
If K
left (more reactants than products)
What is Kw?
the ion product constant for water
What does Ka*Kb equal?
1 x 10^-14 (Kw)
What is pKa?
the pH at the half equivalence point in a titration
What do pKa and pKb equal?
pKa = -logKa pKb = -logKb
What does pKa + pKb equal?
14
What is pH?
a measure of the acidity of alkalinity of a solution
What does strong mean (in terms of acids and bases)?
completely breaks up in water (completely dissociates
True/False: strong acids and bases have very large Ka or Kb values
True
What are common strong acids?
HCl, HBr, HI, H2SO4, HNO3, HClO4
The stronger the acid, the ___ the conjugate base
weaker
The stronger the base, the ___ the conjugate acid
weaker
What are common strong bases?
LiOH, NaOH, KOH, Ca(OH)2, Mg(OH)2, Sr(OH)2, Ba(OH)2 (last 4 are sparingly soluble)
What does a metal oxide and water make?
a metal hydroxide
If temperature increase, K
decreases
If temperature decrease, K
increases
What is the pH of a strong acid/base?
the -log of the given concentration of the acid (becuase it dissociates completely)
How to find the pH of a weak acid or base
1) write out fast and reversible equation
2) write ICE table
3) in initial concentration for weak acid/base write given concentration
4) write in 0’s for everything else in initial concetration
5) set up equilibrium expression and solve for x (avoiding quadratic when you can)
How to find Ka/Kb when given a concentration and the pH
1) write out fast and reversible equation
2) write ICE table
3) find concentration of [H3O+] by using pH = -log[H3O+]
4) plug that value in for every x you see in the ICE table
5) write equilibrium expression and solve for Ka/Kb
What is a polyprotic acid?
an acid that has more than one proton (H+)
The first proton in a polyprotic acid has a ___ Ka than the second
higher
When equilibrating polyprotic acids only the ___ reaction needs to be used
first
What does a buffer contain?
an acid and its conjugate base
What does a buffer do?
resists a change in pH when an acid or base is added to the buffered solution
The more concentrated the buffer, the ___ it resists a change in pH
better
How to find the pH of a buffered solution
1) write out fast and reversible equation
2) write ICE table
3) in initial write given initial concentrations of acid and buffer
4) finish ICE table
5) write equilibrium expression
6) solve for x
7) plug this number into pH = -log[H3O+]
How to find the pH of a buffered solution with an addition of a strong acid
1) write out fast and reversible equation
2) write ICE table
3) find concentration of H+ of the strong acid and subtract it from the concentration of the buffer (find the moles of the strong acid, make mole ratio to find moles of H+, divide moles of H+ by total volume –> volume of bufferd solution and strong acid)
4) solve as you normally would for a buffer
To find a good buffer pair, you want the pH of the buffer as close to the
pKa as possible
What is an ideal mole ratio for a buffer?
1:1
What are the three types of titrations you can have?
1) strong acid & strong base (equivalence point at 7)
2) strong acid & weak base (equivalence point below 7)
3) weak acid & strong base (equivalence point above 7)
What is titration?
the addition of a strong or weak acid or base with a strong or weak acid or base until it reaches equivalence
What is the equivalence point?
when the number of moles of acid equals the number of moles of base
What is the endpoint?
when the indicator changes color
When does a color change happen?
when the pH changes
How to do math for a titration
1) write equation for acid and base
2) write moles, volume, and concentration of each given
3) use stoichiometry to find moles of unknown
What to do if you are asked for pH of solution at equivalence point
(assuming that the titration goes to completion –> no more reactants and any conjugate on the product side reacts with water)
1) add up total volume
2) use mole ratio to find out moles and concentration of product
3) ICE
4) if need be find Kb to solve for x
