ACID Flashcards
you don’t get H+ ions alone in water, but as…
hydroxonium ions H3O+
what is a monobasic acid ?
releases one proton in solution
what is another name for monobasic acid ?
monoprotic acid
what is the conjugate base ?
species that has lost a proton
what is the conjugate acid ?
species that has gained a proton
how is water a special case for conjugate pairs ?
- reacts with acid to form conjugate acid
- reacts with base to form conjugate base
what is the pH scale a measure of ?
[H+]
pH =
-log10 [H+]
Kw =
[H+] [OH-]
what are always the units for Kw ?
mol2 dm-6
why is temp the only variable that will change Kw ?
dissociation of water is endothermic, so warming will shift equil. to right, increasing Kw
for strong monobasic acids, [Acid] =
[H+]
Ka =
weak acids
[H+]^2 / [HA]
pKa =
-log10 Ka
the smaller the value of pKa ..
the stronger the acid
give the definition for buffer
a solution that minimises changes in pH when small amounts of acid or base are added
why can buffers only resist small amount of acid/base ?
the weak acid / conjugate base gets used up
how are acidic buffers made ? (summary)
setting up equilibrium with weak acid and conjugate base
describe first way to make acidic buffer
- mix weak acid w/ the salt of its conjugate base
- salt fully dissociates into ions
- weak acid partially dissociates
describe second way of making acidic buffer
- mix excess of weak acid and strong alkali
- all base reacts w/ acid
- left over weak acid partially dissociates
what does an acidic buffer contain ?
- lots of undissociated acid
- lots of the acid’s conjugate base
- enough H+ ions to make solution acidic
before using a pH probe, what must you do ?
calibrate by placing in distilled water and setting to 7, then to standard solutions of pH 4 and pH 10
what are the axis in pH curves ?
x - vol of alkali added
y - pH
what is the vertical part of a pH curve ?
equivalence point
[H+] = [OH-]
methyl orange from low to high pH
red to yellow
phenolphthalein from low to high pH
colourless to pink
what is Kw at RTP ?
1 x 10^ -14
what assumptions are made for strong acid calc ?
- water dissociation is negligible
- acid fully dissociated [HA] = [H+]
what assumptions made for strong alkali calc ?
- water dissociation is negligible
- alkali fully dissociated
how can aqueous solution of acid contain hydroxide ions ?
water dissociates
what to remember w/ triprotic calculations
multiply [H+] by 3
outline process of making diluted solution for titration
- measure w/ 10cm3 volumetric pipette
- add to 100cm3 volumetric flask
- make up to mark w/ deionised water
- mix well
