Buffers And Neutralisation Flashcards
Define a buffer
A solution that resists changes to pH when small amounts of alkali or acid are added
What are the components of a buffer
Weak acid and its conjugate base
Will the pH of a buffer change
Yes, only slightly
Why might a buffer stop working
When one component is used up
What can be mixed together to form a buffer
Weak acid and the salt of its conjugate base
Weak acid and alkali
Weak acid and some conjugate base
What assumptions are made with buffers
All conjugate base ion comes from the salt
Almost all acid remains undissociated
What will occur is acid is added to a buffer
Conc H+ increases which reacts with A-
So Position of equilibrium moved to the left
What occurs when an alkali is added to a buffer
Conc OH- increases reacts with H+
Conc H+ decreases so position of equilibrium moves to right increasing H+ conc
When are buffers most effective
When conc HA = conc A-
pH=pKa of HA
What is the pH of the blood
7.4
What occurs if the blood is too acidic
Acidosis
What occurs if the blood is too alkali
Alkalosis
How do you create a titration curve using a pH meter
Use pipette to measure 25cm3 of acid
Place electrode in and calibrate to 0
Add alkali to burette and add to acid 10cm3 at a time.
Record pH each interval
Once pH starts to increase rapidly and a drop and measure pH
Once increase begins to slow add 10cm3 at a time again
Stop once pH stays constant
What is the equivalence point
The exact volume of one solution needed to completely react with the other
What is the end point
When the indicator changes colour
HA conc = A- conc of indicator
What are indicators made of
Weak acids
How do you choose an indicator to use
One that has a distinct color change and coincides with vertical section of titration curve
End point = equivalence point
Describe the titration graph of a strong acid strong base reaction
Very low pH at start
Very high pH at end
pH at equivalence is 7
Describe the titration graph of a strong acid weak base reaction
Very low pH at start
high pH at end
pH at equivalence is < 7
Describe the titration graph of a weak acid strong base reaction
low pH at start
Very high pH at end
pH at equivalence > 7
Describe the titration graph of a weak acid weak base reaction
low pH at start
high pH at end
pH at equivalence depends on dissociation
What will occur to a titration curve if the conc of base is increased (base add to set vol of acid)
Shifted to left
What will occur to a titration curve if the conc of base is increased (base add to set vol of acid)
Hh
