Acids & Bases Flashcards
Definition of acid
Proton donor
Definition of base
Proton acceptor
Definition of strong acid
An acid which fully dissociates
Definition of weak acid
An acid which partially dissociates
Definition of pH
pH = -log10 [H+]
Definition of [H+]
[H+] = 10-pH
Ionic product of water (Kw)
Kw = [H+][OH-]
Calculating pH of strong acid
pH = -log10 [H+]
Calculating pH of a strong base
Rearrange Kw = [H+][OH-] to get [OH-]
then use pH = -log10 [H+]
Calculating pH of a weak acid
Ka = [H+]2 ÷ [HA]
and rearrange to get [H+]
Calculating pH of a buffer
Ka = [H+][A-] ÷ [HA]
and rearrange to get [H+]
Acid + Metal →
Acid + Metal →Salt + Hydrogen
Acid + Metal Oxide →
Acid + Metal Oxide →Salt + Water
Acid + Metal Hydroxide →
Acid + Metal Hydroxide → Salt + Water
Acid + Metal Carbonate →
Acid + Metal Carbonate →Salt + CO2 + Water
Examples of strong acids:
HCl
H2SO4
HNO3
H3PO4
Group 1 is called the ‘Alkali Metals’ and Group 2 is called the ‘Alkaline Earth Metals’. As such the oxides of Na and Mg are both alkaline and react with water to form basic solutions
Eg:
Na2O(s) + H2O(l) → 2Na+(aq) + 2-OH(aq
MgO(s) + H2O(l) → Mg(OH)2(aq)
Period 3 Oxides:
Magnesium hydroxide
Magnesium hydroxide is sparingly soluble and so is weakly alkaline
Acids:
Any substance which dissociates to release H+ ions is classed as an acid
Base:
Any substance which will accept and bond to an H+ ion is classed as a base
Definition of amphoteric
When water can act as an acid or a base
Key points of pH scale:
1) The smaller the pH, the greater the concentration of H+ ions
2) A difference of 1 on pH scale means a 10x difference in [H+]
3) It is possible to have a pH below 0 for very strong acids and a pH above 14 for a very strong base
pH for diprotic acids and triprotic acids
eg: H2SO4 & H3PO4
pH = -log10 [H+ × 2]
pH = -log10 [H+ × 3]
Method for weak acid pH calculations:
1) write out dissociation of weak acid
2) construct a Ka expression for the acid
3) simplify Ka expression using [H+]2
4) rearrange expression to get [H+] on its own
5) substitute value of [H+] I to pH equation
pKa
pKa = -log10Ka
Ka
Ka = 10-pKa
Kw is called the ionic product of water and at 298K has a value of 1x10-14mol2dm-6
The value of Kw will alter with temperature
Why is pure water always neutral?
[H+] = [OH-] at all times
