Acids+ Bases Flashcards
Brønsted-Lowry acid
Proton donor
Brønsted-Lowry base
Proton acceptor
Neutralisation of an acid by an alkali
H3O+(aq) + OH-(aq) -> 2H2O(l)
H+(aq) + OH-(aq) -> H2O(l)
Monobasic acid
1 hydrogen ion can be replaced per molecule e.g. HCl
Dibasic acid
2 hydrogen ions can be replaced per molecule e.g. H2CO3
Tribasic acid
3 hydrogen ions can be replaced per molecule e.g. H3BO3
Redox reactions between acids and metals
Acid + metal -> salt + hydrogen
Neutralisation with carbonates
Acid + carbonate -> salt + water + carbon dioxide
Neutralisation with metal oxides
Acid + base -> salt +water
Neutralisation with alkalis
Acid + alkali -> salt + water
pH < 7
Acidic (red)
pH = 7
Neutral (green)
pH > 7
Alkaline (blue)
Low value of [H+]
High pH
High value of [H+]
Low pH
pH calculation
-log [H+(aq)]
Calculation for [H+] (strong acids)
10 ^-pH
Strong acid
Completely dissociates in aqueous solution
Weak acid
Only partially dissociates in aqueous solution
What is Ka
Acid dissociation constant
Ka calculation
[H+] [A-]/ [HA]
When does Ka change
With temperature (standard = 25degrees)
pKa in terms of Ka
pKa = - log Ka
Ka in terms of pKa
Ka =10^-pKa
Stronger acid Ka and pKa
Larger Ka and smaller pKa
Weak acid Ka and pKa
Smaller Ka and larger pKa
Weak acid Ka calculation
[H+(aq)]^2/ [HA(aq)]
2 assumptions when calculation pH of weak acids
1) neglect H+ ions from dissociation of water
[H+]eqm = [A-]eqm
2) [HA]eqm = [HA]initial
pH of weak acid calculation
[H+(aq)] = root (Ka x [HA(aq)]
pH= -log[H+]
Determining Ka experimentally
- prepare standard solution of weak acid of known concentration
- measure the pH of the standard solution using a pH meter
Justifying weak acid assumptions
1) at 25degrees [H+] from dissociation of water = 10^-7. pH>6 = significant [H+]
2) not justified for stronger weak acids with Ka>10^-2 moldm^-3
Kw
Ionic product of water -ions in water multiplied - [H+] [OH-] -1 x 10^-14 = [H+]^2
[H+(aq)] > [OH-(aq)]
acidic solution
[H+(aq)] = [OH-(aq)]
Neutral solution
[H+(aq)] < [OH-(aq)]
Alkaline solution
pH calculation for strong bases
[H+] = Kw/[OH-]
pH= -log[H+]
[H+] for pH x
10^-x moldm^-3
[OH-] for pH x
10^-14-x moldm^-3
