A-Level Chemistry - Acids & Bases
How can we work out what pKa is?
-log10(Ka)
What is the equation for pH?
-log10[H+]
What is the constant for kw?
1.0 x 10^-14
How can we work out Ka using pKa?
10^-pKA
At what temperature is Kw constant?
298K
What is the Bronsted and Lowery Definition of a base?
A proton Acceptor
What is the Bronsted and Lowery Definition of an acid?
A proton Donor
How does the log scale affect the acidity or alkalinity of a solution.
A shift of one pH affects it by 10x
What is a neutral solution?
A solution that has an equal concentration of H+ and OH-
What does a low pKa value show?
A strong acid.
What does a high pKa value show?
A weak acid.
If a HA is an acid then what is its conjugate pair?
A-
What is a conjugate pair?
An acid-base pair that differs by one hydrogen ion.
How do you calculate the pH if there is excess OH- in a strong base and weak acid reaction?
Calculate Concentration [OH-] then use Kw to find [H+] and calculate pH.
How do you calculate the pH if there is excess HA in a strong base and weak acid reaction?
Calculate Moles of HA and A- Calculate [HA] and [A-] then use Ka to find [H+] and then find pH
If A- is a base then what is its conjugate base?
HA
Once something has given away a proton as a acid then what can it do?
It can act as a base.
Where is the equilibrium placed on a reaction when there is a weak acid?
It is further to the left.
Describe the strength of an organic acid?
It is weak.
What is the to work out Ka for a weak acid?
Ka = [H+]^2/[HA]
What is a strong acid?
One that is virtually 100% ionised when dissolved in water.
What is a weak acid?
One which does not fully ionise when dissolved in water.
How is the concentration of hydrogen ions affected when the molecule is diuretic?
The concentration is doubled
What is pH relative to?
The concentration of Hydrogen ions in the solution.
How can we measure the strength of an acid?
The extent to which an acid dissociates.
How do you calculate the pH if HA = A- in a strong base and weak acid reaction?
Use Pka to find pH
What is the formula for finding the H+ Concentration
[H+] = 10^-pH
How else can we assume the Ka formula?
[H+] = [A-] [HA]start = [HA]Eqm
What is the formula for Kw of water
[H+][OH-]
What does a weak acid and a weak base curve look like?
There is not a sharp enough equivalence point as they are usually not titrated against each other. There is no steep drop for neutralisation.
Why would you use pKa?
To make a more useable scale as Ka units are quite small.