Acids, Bases and Buffers Flashcards
Define an acid
Proton donor
Define a base
Proton acceptor
Give an example of a monobasic acid
HCl
Give an example of a dibasic acid
H2SO4
Give an example of a tribasic acid
H3PO4
Identify the acid-base pairs for the below reaction:
CH3COOH + H2O <———> CH3COO- + H3O+
A1 B2 <———> B1 A2
Define strong acid
Acid that completely dissociates
Give some examples of strong acids
HCl
H2SO4
HNO3
What is the difference between concentrated and strong
concentration means many mol per dm3 whereas strong refers to amount of dissociation
Define weak acids
Acids that only partially dissociate
Give some examples of weak acids
Any organic acid
What is the constant used to measure the extent of acid dissociation called
Acid dissociation constant (Ka)
Write the acid dissociation constant expression
[Ka] = [H+][A-]/[HA]
What does a larger Ka value mean
Greater extent of dissociation
equation to convert Ka to pKa
pKa= -log[Ka]
Equation to convert pKa to Ka
Ka=10^-pKa
What is the relationship between pKa and the strength of the acid
smaller the pKa the stronger the acid
Equation to convert [H+] to pH
pH= -log[H+]
Equation to convert pH to [H+]
[H+]= 10^-pH
What is the relationship between pH and [H+]
High pH means low [H+]
Write equation to calculate [H+] of a weak acid
√[Ka][HA]
What assumption can be made when calculating pH of weak acid
[H+]=[A-]
Write an expression for the ionic product of water , Kw
Kw = [H+][OH-]
What is the units for Kw
Mol2dm-6
What is the value of Kw at 298K
1x10-14
What physical factors affect Kw and how
Only temperature, if increased equilibrium moves right so Kw increases and pH of pure water decreases
Indices of [H+] and [OH-] always add up to what
-14
Define the term strong base
Base the dissociates 100% in water
Give some examples of strong bases
NaOH
KOH
Ca(OH)2
Give example of weak base
Ammonia
Write the equation to calculate [H+] of strong bases
[H+]= Kw/ [OH-]
Define a buffer
A mixture that minimises pH changes on addition of small amounts of acid or base
What are two ways in which buffers can be made
Weak acid and its conjugate base
Weak acid and a strong alkali
Which way does equilibrium shift when acid is added to a buffer solution and why
Equilibrium shifts to the left to minimise increase of [H+], forming more [HA]
In which direction does equilibrium shift when alkali is added to a buffer solution and why
Equilibrium shifts to the right to minimise decrease in [H+]
[H+] + [OH-] ——-> H2O
Define the term equivalence point
The point at which the exact volume of base has been added to just neutralise the acid
What are the properties of a good indicator for a reaction (3)
Sharp colour change
End point should be the same as the equivalence point
Distinct colour change so you can tell when the end point has occured
