Acids and Bases Flashcards
Equation for calculating pH
-log10[H+(aq)]
A small pH=
a high concentration of H+ ions (so a low concentration of OH- ions).
A large pH=
a low concentration of H+ ions (so a high concentration of OH- ions).
What does one pH unit correspond to?
A decrease in pH means an increase in H+ ions by a factor 10.
Equation for concentration of H+ ions
[H+] = 10^-pH
Kw equation
Kw = [H+] x [OH-] mol2dm-6
It is the ionic product of water (water ionises slightly).
Kw at 298K
1x10^-14 mol2dm-6.
What is required in a neutral solution in terms of ions?
[H+] = [OH-]
For every mole of water that dissociates, you would get an equal amount of H+ and OH- ions.
How does a low temperature affect pH?
A low temperature increases the pH because the concentration of H+ ions decrease. This is because the reaction is exothermic, so the backward reaction is favoured at equilibrium and more reactants are made (H2O).
How does a high temperature affect pH?
A high temperature decreases pH because the concentration of H+ ions increases. The reaction is endothermic so the forward reaction is favoured.
Kw equation (only for pure water)
Kw = [H+]^2
pKw equation
pKw = -log10Kw
To convert, use 10^-pKw
Strong monobasic alkalis
[OH-] = [alkali]
Releases 1 OH- ion.
Strong dibasic alkalis
[OH-] = 2[alkali]
Releases 2 OH- ions, have to multiply the [H+] concentration by 2 during calculations.
Weak acids and bases definition
They only partially dissociate into their ions when dissolved in water.
