buffers Flashcards
Situation = Add NH4Cl to aq solution of ammonia Effect = le chateliers (explain) and what is it called in relation to buffers
pH is higher, system shifted to the left (side without H+)
Called the common ion effect
What are buffered solutions
Solutions that resist change in pH when acids or bases are added
What do buffers contain
Weak acid and weak base conjugate pair
How can buffers be prepared
Mixing solutions together
Dissolving solids in solutions
Acid-base titrations
What do reactions involving strong acids or bases do
Go to completion
State the 3 cases of reactions which go to completion
Strong acid with strong base
Weak acid with strong base
Strong acid with weak base
What are the 2 steps to solving buffers
Stoichiometry calculations
Equilibrium calculations
What are the first 2 things to do for a buffer question
Identify question as a buffer solution (conjugate pair)
Write out reaction (make sure to use right component)
How do you do the stoichiometry calculations
Find mols of each component
Reactant - (OH- or H+)
Product + (OH- or H+)
All of OH- or H+ is consumed = 0 mol
What are the last 2 things to do for a buffer question
Equilibrium calculations (ICE or HH) Calculate pH
What controls the buffering capacity & the concentration of H+ & pH
Controlled by magnitudes of HA & A-
HA/A-
Equilibrium concentrations of HA & A- =
approx initial concentrations
State HH equation
pH = pKa + log [A-]/[HA] pH = pKa + log [bases]/[acid]
When can we use HH equation
Ratio of A-/HA is within 0.10< A-/HA <10
Molarity of each buffer component exceeds Ka by a factor of at least 100
Explain optimal ratio for buffers
1:1
pH = pKa + log (1)
pH=pKa
When selecting components pick acid with a pKa value closest to desire pH value
