Acids, Bases And Buffers Flashcards
Write the equation for the dissociation of water
Why does water have a pH of 7
Only source of hydrogen/ hydroxide ions is from water so [ hydrogen ions]=[ hydroxide ions]
How do you calculate pH
What does a buffer do
Resists ranges in pH upon the addition of a small amount of acids/base
Write the equation (using displayed formula) for the deprotonation of ethanoic acid
Write the general equation for the dissociation of an acid
How do you calculate Ka
What is the Henderson- hasselbach equation
What does it mean if pH=pKa
How do you calculate the ph of water using the Kw expression
Kw = 10^-14
Concentration of base would be given
Substitute conc. Of base into Kw expression
Kw\concentration of base=conc. of H+
- log [H+]= pH
What does HA and A- mean
A- is the negative ion formed from the dissociation of the acid
HA is the acid in its normal protonated form
What is the equation for the dissociation of a base
What is the Henderson- hasselbach equation to find the ph of a base
What is the general shape titration curve for a strong acne and strong base
What is the general shape for the titration curve of a strong base with a weak acid
How does a weak acid - string base buffer work
A weak acid-strong base buffer works by using the weak acid and its conjugate base to resist changes in pH when small amounts of strong acid or strong base are added
Weak acid partially dissociates
When base added = OH- ions from added base reacts with H+ from weak acid in buffer to form water
As H+ used, the equilibrium shifts to the right to produce more H+ ions from the dissociation of HA
When acid added= H+ from added acid react with A- from weak acid in buffer to prose more weak acid
As A- used, equilibrium shifts to left to produce more A- from dissociation of HA
What occurs at the equivalence point
pH = pKa
[A-]=[HA]
What happens in the buffering period
Buffer would change by +/- 1 pH unit
what does ‘pH is independent of dilution mean ‘
Why does phosphoric acid have multiple pKa’s
Because it can undergo multiple dissociations
What is the general shape of a phosphoric acid titration curve plus the corresponding dissociations occluding at each buffering period (+ the pKa at each dissociation)
What does a small pKa mean
The smaller the pKa the stronger the acid (so it will dissociate more strongly)
What can a strong acid do
Dissociate fully in water
What is the bronsted Lowry definition of an acid and base
What is the Arrhenius definition for an acid /base
What is the general equation for an acid-base reaction
What happens when acid is added to a buffer
- Conc. Of H3O+ increases
- Equilibrium shifts to the left to counteract change 3. H30+ combine with conjugate base (A-)to form more acid
What happens when base is added to a buffer
- OH- reacts with undissociated acid → produces salt and water (neutralisation reaction)
- Salt dissociates to produce more A-
Why is a strong acid /base not used to produce a buffer
Their equilibrium position lies far to the right
The backwards reaction rarely occurs (so strong acid/base would completely dissociate)
a buffer must consist of a mixture of a weak conjugate acid-base pair.
How do acids / bases behave in aqueous solution + what is the general equation for the reaction of bases in water
How would you find the ratio of [HA]/[A-]
Ratio of [A-]/[HA] found using Henderson hasselbach
1/[A-]/[HA]
