3.1.12- Acids and Bases Flashcards
What is a brønsted Lowry acid
Proton donor
What is brønsted Lowry base
Proton acceptor
What is a brønsted Lowry reaction
Reaction involving the transfer of a proton
What is a monoprotic acid
Acid that released one H+ ion per molecule
Eg HCl,HNO3
What is a diprotic acid
Acid that release two H+ ions per molecule
Eg H2SO4
Definition of ph
PH = -log(H+)
[H+] = 10^-pH
What is Kw
Kw=[H+][OH-]
What is Kw value
1.00x10-14
Effect of temperature on Kw
As temperature increases the equilibrium moves right to oppose increase in temperature
So [H+] and [OH-] increases
Kw increases and pH decreases
How to find ph of strong bases
[H+] = Kw/ [OH-]
Find ph of mixture of strong acid and strong based
Excess H+
Mol H+ Mol OH- Xs mol H+ Xs [H+] =n/v pH= -log[H+]
Find ph of mixture of strong acid and strong based
Excess OH-
Mol H+ Mol OH- Xs mol OH- Xs [OH-] = n/v [H+] = Kw/[OH-] -log[H+]
What is a weak acid or base
Only partially dissociated
Acid dissociation constant
Ka= [H+][A-]
—————
[HA]
pKa=-logKa
Ka= 10^-pKa
What does a bigger value of Ka mean or smaller value of pKa mean
A strong acid
Find pH of weak acid
Ka=[H+]^2
———
[HA]
pH=-log[H+]
Reactions of weak acids
XS HA
1) mol of OH- left and A- formed
2) [HA] left over [A-] left
3) use Ka to find [H+]
4) find pH
Reactions of weak acid
Xs OH-
1) [OH-]
2) Kw to find [H+]
3) find pH
Reactions of weak acids when mol HA =OH-
pH= pKa of weak acid
What is an indicator
Weak acids were HA and A- are different colours
Low pH HA present more
High pH A- present more
What is methyl orange
When Red more HA
When yellow more A-
Changes at 3.2-4.4
What is phenolphthalein
More HA is colourless
More A- is pink
Changed between 8.2-10.0
What does equivalence point show
Where moles of alkali = moles of base
What is an end point
Where the indicator changes colour
Show what ph graph with weak acid base and strong acid base
Draw
How to calculate pH of buffer when acid added
A-+H+ —-> HA
Mol H+ added
Work out [HA] and [A-] left
Ka= [H+][OH-]
—————-
[HA]
-log[H+]How to calculate pH of buffer when base added
Mol OH-
HA+ OH- —> A- + H2O
[HA] and [A-]
Ka = [H+] [A-]
————
[HA]
pH = -log[H+]
What do buffer depend on
Ratio of HA to A- when small amount of acid or alkali added this does not change very much
What is an acid buffer made from
Weak acid and salt of weak acid
What is base buffer made out of
Weak base and salt of weak base
