12P- Acids And Bases Flashcards
Definition of an acid
Proton donator
Definition of a base
Proton acceptor
What happens at an acid base equilibrium
The transfer of protons
Why is the pH scale logarithmic
pH scale measures H+ ion conc
In an aqueous solution H+ conc can cover a large range
Equation to calculate pH
-log[H+]
Equation to calculate H+ conc
[H+]= 1x 10^-pH
How many decimal places is pH given to
2 dp ALWAYS
How to calculate pH of a strong acid when given its conc
Monoprotic acid, same [H+] in moles/conc
Diprotic acid, double [H+] in moles/conc
Sub this value into pH= -log[H+]
What happens when water is ionised
Disassociates slightly
H2O(l) <—> H+(aq) + OH-(aq)
How is Kw derived and what the equation
From equilibrium constant Kc
Kc= [H+][OH-]/ [H2O]
Kc[H2O]= [H+][OH-]
H2O is much larger than the conc of any of the ions, assume it’s value is constant, make LHS equal to Kw
Kw= [H+][OH-]
What effects the value of Kw
Temperature
How to is Kw to calculate the pH of a strong base from its conc
Value of Kw at specific temp should be given
Sub [OH-] into Kw eq, to find [H+]
Sub [H+] into pH eq
Definition of weak acids and weak bases
They disassociate slightly in aqueous solutions
What’s Ka and form an equation
Disassociation constant for a weak acid
HA(aq)—> H+(aq) + A-(aq)
Ka= [H+][A-]/[HA]
Equation for pKa
pKa= -log10(Ka)