Topic 8: Acids & Bases Flashcards
A Brønsted-lowry acid
A Brønsted-lowry acid is a proton donor
It must contain hydrogen
Brønsted-lowry base
A Brønsted-lowry base is a proton acceptor
It must have a lone pair of electrons to accept a proton
Conjugate acid-base pairs
Two species that differ by a proton are called conjugate acid-base pairs
Every Brønsted-lowry reaction has 2 conjugate acid-base pairs
e.g acid 1 and base 1
or
acid 2 and base 2
Amphiprotic species
An amphiprotic species is a species that can act as both an Brønsted-lowry acid and a Brønsted-lowry base
e.g Water (able to donate or accept a proton)
Types of reactions that acids undergo
- Neutralisation reactions with bases such as metal hydroxides, metal oxides, and ammonia
- Reactions with metal carbonates and metal hydrogen carbonates
- Reactions with active metals such as magnesium or zinc
Acid + metal —> ?
Salt + water
Acid + metal oxide —> ?
Salt + water
Acid + ammonia —>
e.g HCl + NH3
NH4Cl
Acid + metal carbonate —>
Salt + water + carbon dioxide.
Acid + metal hydrogen carbonate —> ?
Salt + water + carbon dioxide
Acid + metal —> ?
Salt + hydrogen
Thermometric titration
A thermometric titration can be carried out to determine the concentration of a solution
An acid of unknown concentration is added to a base of known volume and concentration
The temperature of the mixture is recorded as the acid is added to the base and the results are plotted on a graph
The maximum temperature reached signifies the end-point of the titration
The pH scale
What is the formula for pH?
What is the formula for [H+]?
The pH scale is used to measure how acidic or basic a substance is
pH = -log [H+]
[H+] = 10^-pH
What happens to pH when there is x10 increase in H+ ions?
pH decreases by 1.
If H+ ions increase by x100, pH decreases by 2.
Difference between strong acids and weak acids
Strong acids fully dissociate into their ions
Weak acids only partially dissociate into their ions
The autoionisation of water
When water dissociates to form hydronium and hydroxide ions.
Concentration of H+ ions vs concentration of OH- ions
When the concentrations are equal = the solution is neutral (pH is 7)
When there is a higher concentration of H+ than OH- = the solution is acid (pH is less than 7)
When there is a higher concentration of OH- ions than H+ ions =. the solution is basic (pH is more than 7)
Calculating concentrations of ions from Kw:
How to calculate concentration of H+?
How to calculate concentration of OH-?
[H+] = Kw / [OH-]
[OH-] + Kw / [H+]
Formula for Kw
Kw = [H+][OH-]
Where does the position of equilibrium lie for a strong acid?
Where does the position of equilibrium lie for a weak acid?
For a strong acid, the position of equilibrium lies to the right.
For a weak acid, the position of equilibrium lies to the left.
