Chapter 20 - Acids, Bases and pH Flashcards
What is the Bronsted-Lowry definition of an acid
- Proton donors
- When acids are dissolved in water, H+ ions are released
What happens to H+ ions in water?
- They don’t exist on their own in water
- They form hydroxonium ions (H3O^+)
- Hydoxonium ions are what make a solution acidic
What is the Bronsted-Lowry definition of a base?
- Proton acceptors
- When dissolved in water, they react to form OH- ions
What are polyprotic acids?
- Some acids donate more than one proton (polyprotic) or polybasic
Is Nitric Acid Polyprotic?
HNO3 is monoprotic
Is sulphuric acid polyprotic?
H2SO4 is diprotic
Is phosphoric acid polyprotic
H3PO4 is triprotic
What is a neutralisation reaction
When an acid reacts with a base to produce a salt which is pH neutral
How does Ammonia react with water to produce Hydroxide ions?
Accepts a proton to produce an Ammonium ion and hyrdoxide ion.
NH3 + H2O –> NH4+ + OH-
How does Ammonia react with acids
to produce an ammonium salt (no water)
Metal and acid
Salt and hydrogen
Metal oxide and acid
salt and water
metal hydroxide and acid
salt and water
Metal carbonate and acid
salt, carbon dioxide and water
What are conjugate acids and conjugate bases
- A conjugate acid has GAINED the proton
- A conjugate base has LOST the proton
What is a strong base/acid
dissociate with ions completely
What is a weak base/acid
partially dissociate when dissolved in water
Examples of weak acid
- organic acids
- equilibrium lies to the left, backwards reaction favoured strongly
Examples of weak bases
- Ammonia
- Backwards reaction favoured heavily
How does water behave as a base in the presence of acid
accepts a proton to form a hydroxonium ion (H3O^+)
How does water exist
it exists in equilibrium with its ions
Equation for ionic product of water Kw
is Kw a constant
The value of kw is the same in a solution for a given temperature
What is the equation for finding pH
Assumptions made to simplify Kw equation
- Pure Water has same concentration as OH- and H+ ions
so for pure water Kw = [H+]^2
Calculating the pH of a strong diprotic acid when given the concentration of the acid
- produces 2 H+ ions for every molecule of acid
- [H+] is 2x the concentration of the acid
How to work out pH of a strong acid
Use Kw expression to find out [H+]
Why is it harder to calculate the pH of weak acids
because they do not dissociate fully
How to calculate the pH of a weak acid? What are the assumptions made?
By using Ka equation bellow.
What is pKa? do strong acids have low or high pKa?
It is another way of measuring the strength of an acid
- the lower the value, the stronger the acid
