Acids And Bases Flashcards
Define a Brønsted-Lowry acid
Proton donor
Define a Brønsted-Lowry base
Protons acceptor
What ion causes a solution to be acidic
Name and formula
H+ or more accurately H3O+ (Oxonium ion) as protons react with H2O to form it
What ion causes a solution to be alkaline
-OH
Write an equation for the ionisation of water
2H2O H3O+ + -OH
H2O H+ + -OH
Derive Kw using the equation for the ionisation is water
Kc = [H+] [OH-]
[H2O]
As [H2O] is so large compared to the other concentrations the concentration can be considered to be constant
Kw = [H+] [ OH-]
What is the value of Kw at 298K
1 x 10^-14
What physical factors affect the value of Kw
How do the affect it
Temperature - 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 pH does not equal 7
[H+] = [ OH-]
Give an expression for pH in terms of H+
pH = -log10[H+]
What is the relationship between pH and concentration of H+
Lower pH the higher the concentration of H+
Of two solutions have a pH different of 1 what is the difference in [H+]
X10
How do you find [H+] from pH
10^-pH
How do you find [OH-] from pH in standard conditions
Find [H+] use Kw to calculate [OH-]
What is the different when finding [H+] from the concentration of diprotic and triprotic acids
Need to multiply 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
Define the term strong base
One which fully dissociates in water
What is the difference between concentrated and strong
Concentrated means many mil per dm3
Strong refers t amount of dissociation
What is a weak acid and a weak base
Weak acids and bases do not fully dissociate in water
They only partially dissociate into their ions
Examples of strong acids
HCl
H2SO4
H3PO4
Examples of strong bases
NaOH
CaCO3
Na2CO3
Examples of weak acids
CH3COOH
Any organic acid
Examples of weak bases
NH3
What is Ka
Ka = [H+][A-]
[HA]
How would you work out the pH of a weak acid
Use Ka
Then pH = -log[H+]
What is a titration
The addition of an acid/base of known titration to a base/acid of unknown titration to determine the concentration
An indicator is used to show that neutralisation has occurred or a pH meter
Describe titration curve for strong acid with a strong base
High
Gradually decrease
Quick decrease then levels off
Titration for a strong acid with a weak base
pH of about 9
Slight decrease
Quick decrease
Levels off
Titration curve for a weak acid with weak base
Ph of about 9 Slight decrease Slight increase Quick decrease Levels off
Titration curve for a weak acid and strong base
High pH
Levels off
Quick decrease
Levels off
Define equivalence point
The point at which the exact volume of base has been added to just neutralise the acid
What generally happens to the pH of the solution around the equivalence point
There is a large and rapid change in pH
What is the end point
The boiling of acid or alkali added when the indicator changes colour
If the right indicator is chosen then the equivalence point = end point
What are the properties of a good indicator
Sharp colour Change
End point list be the same as the equivalence point
Distinct colour change
What indicator would you use for a strong acid base titration
Phenolphthalein
What indicator would you use a strong acid weak base titration
Methyl orange
What indicator would you use for a weak acid and strong base titration
Phenolphthalein
What indicator would you use for a weak acid weak base titration
Neither methyl orange or phenolphthalein
Methyl orange
Red in acid
Yellow in alkali
Changed at pH 4-5
Phenolphthalein
Colourless in acid
Red in alkali
Changes at pH 9-10
What is the half neutralisation point
When volume = half the volume that has been added at the equivalence point
Define a buffer solution
A solution that resists changes in pH when small amount of acid/alkali are added
What do acidic buffer solutions contain in general
A weak acid and a soluble salt of that acid that fully dissociates
Equation for an acidic buffer with added acid
A- + H+ -> HA
Equation for acidic buffer with added alkali
HA + OH- -> H2O + A-
What do basic buffer solutions contain in general terms
Weak base and soluble salt of that weak base
How can you calculate the pH of buffer solutions
Ka of weak acid
pH = -log[H+]
Which buffer system maintains blood pH
H+ + HCO3- CO2 + H2O
