C20 Acids, Bases, And pH Flashcards
Define a Bronsted-Lowry acid
Proton donor
Define a Bronsted-Lowry base
Proton acceptor
What ion causes a solution to become acidic? (2 marks) Name and formula
H+ or more accurately H3O+ as protons react with H2O to form it.
What ion causes a solution to be alkaline?
-OH (hydroxide ion)
Write the equation for the ionisation of water
2H2O (l) (reversible reaction) H3O+(aq) + -OH(aq)
H2O (l) (reversible reaction) H+(aq) + -OH(aq)
Give an example of a monobasic acid.
HCl
Give example of a dibasic acid
H2SO4
Give an example of a tribasic acid
H3PO4
Define a strong acid
An acid that completely dissociates in (aq) to release H+
Give examples of strong acids
HCl
H2SO4
HNO3
What is the difference between concentrated and strong?
Concentrated means many mol per dm3
Strong refers to amount of dissociation
Define weak acid
An acid that only partially dissociates in aq to release H+
Give examples of weak acids
Methanoic acid
Any organic acid
What is the constant that is used to measure the extent of acid dissociation called?
Acid dissociation constant
What is the symbol of acid dissociation constant?
Ka
What does a larger Ka value mean?
Larger the Ka - greater the extent of dissociation
Write the equation used to convert Ka into pKa.
pKa = -log(Ka)
Write the equation used to convert pKa into Ka.
Ka = 10^-pKa
What is the relationship between pKa and the strength of the acid?
Smaller the pKa stronger the acid
What is the equation used to convert concentration of H+ into pH.
pH = -log[H+]
Write the equation used to convert pH into concentration of H+
[H+] = 10^-pH
Why is the pH scale useful compared to concentration of H+?
pH scale allows a wide range of H+ concentration to be expressed as simple positive values.
What is the relationship between pH and [H+]?
High pH value means a small [H+]
If two solutions have a pH difference of 1, what is the difference in [H+]?
A factor of 10
[H+] of a strong acid is equal to what?
[H+] = [HA]
What is the assumption made when calculating pH of weak acids?
It is assumed that the concentration of acid at equilibrium is equal to the concentration of acid after dissociation. This is because only very little of the acid dissociates.
Write the expression for the ionic product of water, Kw
Kw = [H+][OH-]
What is the units for Kw?
Mol^2dm^-6
What is the value of Kw at 298K?
1.0 x 10^-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.
Indices of [H+] and [OH-] always add up to what value?
-14
Define the term strong base
Base that dissociates 100% in water
Give examples of strong bases
NaOH
KOH
Ca(OH)2
Give an example of a weak base
Ammonia
Write the equation used to calculate [H+] of strong bases
[H+] = Kw / [OH-]
Define a salt
The product of a reaction in which the H+ ions from the acid are replaced by metal or ammonium ions.
PMT = a compound that is formed when H+ of an ion is replaced by a metal ion or positive ion.
What is the definition of Kw?
The temperature dependent constant that represents the dissociation of water into H+ and OH-.
Define strength of acids and bases
A measure of the relative degree of dissociation of an acid or base (where strong means complete dissociation and weak means partial dissociation).
Define a conjugate acid-base pair
Contains 2 species that can be interconverted by transfer of a proton.
Define an alkali
A soluble base that dissociate in aq to release OH-
Define a base
An insoluble compound that neutralises an acid to form a salt.
Define Ka
The equilibrium constant that shows the extent of dissociation of a weak acid.
