Acids, Bases and Buffers Flashcards
Define a Bronsted-Lowry acid
Proton donor
Define a Bronsted-Lowry base
Proton acceptor
What ion causes a solution to be acidic? (Name and formula)
H+ ion or more accurately H3O+ (oxonium ion) as protons react with H2O to form it
What ion causes a solution to be alkaline
-OH (hydroxide ion)
Write an equation for the ionisation of water (2)
2H2O (l) ⇌ H3O+ (aq) + -OH (aq)
OR
H2O (l) ⇌ H+ + -OH (aq)
Derive Kw using the equation for ionisation of water
K= [H+][OH-] / [H2O]
[H2O] K = [H+][OH-]
[H2O] is so large compared to [H+] and [OH-] that [H2O]K can be considered a constant. [H2O] K = Kw
Therefore Kw = [H+][OH-]
What is the value of Kw at 298K
1.0 x10^-14
What physical factors affect the value of Kw? How do they affect it?
Temperature only - if temperature is increased the equilibrium moves to the right so Kw increases and the pH of pure water decreases
Why is pure water still neutral even if the pH does not equal 7?
[H+] = [OH-]
Give an expression for pH in terms of H+
pH = -log[H+]
What is the relationship between pH and [H+]
Lower pH = higher concentration of H+
If two solutions have a pH difference of 1, what is the difference in [H+]
A factor of 10
How do you find [H+] from pH?
[H+] = 10^-pH
How do you find [OH-] from pH? (at 298K)
Find [H+], use Kw (equal to 1 x10^-14 at 298K) to calculate [OH-]
What is different when finding [H+] from the concentration of diprotic and triprotic acids
Need to multiple the concentration of the acid by the number of protons to find [H+]
How do you calculate the pH of a strong alkaline solution?
Use Kw to calculate [H+] from [OH-]
Use pH = -log[H+]
Define the term strong acid
One which fully dissociates in water (HX —> H+ + X-)
Define the term strong base
One which fully dissociates in water (XOH —> X+ + OH-)
What is the difference between concentrated and strong
Concentrated means many moles per dm3, strong refers to amount of dissociation