Ch3 Acids, Bases and Buffers Flashcards
Conjugate acid-base pairs
HA + B <=> BH+ + A-
base + acid <=> conjugate acid + conjugate base
Conjugate acid
Species with extra proton
Conjugate base
Species without proton
Mono,di or tribasic acids
acids can produce more than one conjugate base depending on how many hydrogen ions they donate
Strong acids
highly ionised in aqueous solution to produce H+ ions
Weak acid
partially ionised in aqueous solution to produce H+ ions
Acid dissociation constant
[HA(aq)]
Hydrogen ion conc of strong acid using Ka
strong acids ionised completely so have same H+ conc as HA conc
Hydrogen ion conc of weak acid using Ka
[H+] = square root Ka x conc of solution
because [H+] is same as [A-]
pH formula
-log[H+]
Hydrogen ion conc from pH
10^-pH
Ionic product of water Kw
[OH-][H+] = 1x10^-14
Buffer solution
solution that resists a change in pH when a small quantity of acid or alkali is added
Key points for buffer solution
weak acid + salt from acid
Adding alkali to buffer solution
OH- reacts with H+ on right side equilibrium to produce H2O so [H+] decreases
pH increases
Equilibrium shifts to right to counteract so [H+] increases
pH decreases
Add acid
H+ increases [H+] conc
pH decreases
equilibrium position shift to left to counteract
[H+] decreases
pH increases
ka buffer solution
[salt][H+] / [acid]
= ka
pH buffer solution
-log(Ka[acid] / [salt])
Strong acid
HCl
HNO3
H3PO4
H2SO4
Strong base
NaOH
metal hydroxides
Weak acid
CH3COOH
Weak base
NH3
Equivalence point
enough acid has been added to react completely with all of the base
Phenopthalein
acid - colourless
pink-alkali
changes around pH9
methyl orange
acid- red
base- yellow
change around pH 4
