Acids and Bases Flashcards
what is the equation for the self- ionistaion of water ?
H20 + H20 ——–> H30+ + OH-
why is water known as an amphoteric ?
- water acts as a base and as an acid
what is the equation for Kw?
- Kw = [H30+] [OH-]
what is the value of Kw at 25c
- 1 x 10-14
why does Kw increase with temperature ?
- ionisation of water is an endothermic process
what is the relationship between PH,Ka and Pka
- high ka = stronger acid = smaller Ph
- larger ka = smaller pka
how do u calculate pOH ?
- log[OH-]
what equation links pH and pOH ?
- pH +pOH = 14
what is the equation for Ka ?
Ka = [H3O+][A-] / [HA]
OR
Ka = [H3O+]^2 / [HA]
what is equation for Kb ?
Kb = [HB+][OH-] / [B]
what does a more electronegative atom on the acid mean ?
-conjugate base is more stable
how does anion size affect acidity ?
- increasing size = increased acidity
- as size increases, bond between H and ion is easier to break
- so H+ is more easily donated
how does strength of the acid affect strength of conjugate base ?
- stronger acid = weak conjugate base / stable
what is delocalization ?
- charge is spread out across a molecule because e- are free to move
how does delocalization stabilize a molecule ?
- delocalization allows for resonance structures and stabilization
which is more stable a weaker or stronger conjugate base ?
- weaker conjugate base
why is acetate ion more stable than ethoxide ion ?
- e - are localised in ethoxide
- no resonance structures
- so less stable
How does the inductive effect increase acidity ?
- halogens are more electronegative
- pulls e- towards itself
- pulls e- through sigma bonds
- this decreases electron density
- base is more stable/ weak
- acid is stronger
How does hybridization affect acid strength ?
- atoms with higher percent of s character are more acidic
- lone pair is held closer to nucleus
- more stable / weaker conjugate base
what is the s character of a hybrid orbital ?
- percentage of s in it
- sp = 50
- sp2 = 33
- sp3 = 25
what is a Bronsted-Lowry acid ?
- proton donor
what is a Bronsted-Lowry base ?
- proton acceptor
what is a Lewis acid ?
- electron pair acceptor
what is a Lewis base ?
- electron pair donor
what factors determine the stability of a conjugate base ?
- electronegativity
- size of anion
- resonance
- hybridization
- inductive effects
HEIRS
how does electrongeativity affect strength of an acid ?
- created a polar bond, H becomes more positive so it is easier to break the bond
Are all Bronsted Lowry acids Lewis acids?
Yes, but not all Lewis acids, are Bronsted Lowry acids
How do you know if salt is more acidic or basic ?
- need ka and kb values whichever is greater dominates
What is the common ion effect ?
- shift in equilibrium caused by addition of a compound that has an ion in common with the dissolved substance
what effect does a common ion have on ionisation of a weak acid/base ?
- suppresses ionisation
- because equilibrium shifts to favour reactants so less H+ /OH- conc
What is the effect of having a weak acid and its salt in solution ?
- creates a buffer solution
- ionisation of HA suppressed by presence of A-
- hydrolysis of A- suppressed due to HA
what happens if a strong base is added to a buffer?
- HA+ OH- —> A-+H20
- pH only changes slightly
what happens if a strong acid (HCL) was added to a buffer ?
- HCl—> H+ +Cl-
- H+ + A- –> HA
- slight change in pH
What is a buffer ?
- minimises change in pH upon addition of a small amount of acid or base
- made of weak acid + conjugate base
what is the halfway point of weak acid / strong base titrations ?
- [HA] = [A-] so pka = pH
what is the Henderson-Hasselbalch equation and what is it used for ?
- used to find the pH of a buffer
- pH = pKa + log [A-]/[HA]
what happens to blood pH when you hypo-ventilate ?
- acidosis - pH drops
what happens to blood pH when you hyperventilate
- alkalosis - rise in pH
What happens when
blood pH drops ?
- increased conc of H2CO3 by protonation of HCO3-
- H2Co3 looses water to form CO2aq which is coverted to co2 gas
What happens when blood ph rises ?
- inc conc of hco3- by deprotination of H2CO3, breathing rate changes
Anti-log of Henderson equation
[acid] / [base]= 10^(pKa-pH)
What is the Henderson Hasselbalch equation ?
pH = pKa + log [A-] / [HA-]
What is equation % acid = 100 /1 + 10^(pH - pKa)
- if group is acidic gives % of unionised
- if basic group gives % ionised
