acids and bases Flashcards
pH
The pH of a solution is a measure of its hydrogen ion concentration and thus its acid-base characteristics. High hydrogen ion concentration, that is an acidic solution, corresponds to a low pH. Basic solutions have a high pH. Pure water is neutral and has a pH of seven. Dissolving an acid or base in water will change his pH. Adding an acid raises the concentration of hydrogen ions thus Lowering the pH. Adding a base to water raises the hydroxide ion concentration and causes the hydrogen ion concentration to fall causing the pH to rise.
arrhenius theory: acids
an acid is a substance that will ionise in a solution producing H+ (aq) ions.
arrhenius theory: bases
A base is a substance that will dissociate in solution releasing OH- (aq) ions
acids: oxides
non-metal oxides
bases: oxides
metal oxides/hydroxides
ionisation
Acids have a covalent molecular structure and so don’t actually contain hydrogen ions. However, when dissolved in the water they produce hydrogen ions in a reaction called ionisation. This will result in the formation of hydrogen ions
dissociation
Bases are all ionic hydroxide compound. These compounds contain metal ions and hydroxide ions. When dissolved in water these ions are released into solution. This process is called dissociation
strong acids
Arrhenius theory States that strong acids dissolve in water to undergo complete ionisation. Thus all the dissolved acid converts into ions. A single arrow in the ionisation equation shows this.
strong acids vs weak acids
always produce a more vigorous reaction than weak acids
a strong acid will produce a higher hydrogen ion concentration than weak acids
weak acid
the theory identifies a weak acid as one that undergoes partial ionisation which means that the remaining is mostly in the form of unionised molecules. Double arrows show the partial nature of this reaction.
strong acids: examples
- HCl (hydrochloric acid)
- H2SO4 (sulfuric acid)
- HNO3 (nitric acid)
weak acids: examples
- CH3COOH (ethanoic acid)
- C6H8O7 (citric acid)
- H2CO3 (carbonic acid)
- H3PO4 (phosphoric acid)
- H2SO3 (sulfurous acid)
- HSO4- (hydrogen sulfate ion)
strong bases
strong bases are group 1 or 2 metal oxides/hydroxides
- NaOH (sodium hydroxide)
- Ca(OH)2 (calcium hydroxide)
- MgO (magnesium oxide)
weak bases
- CuO (copper (II) oxide)
- NH3 (ammonia)
- NaHCO3 (sodium hydrogencarbonate)
acids: characteristics
- tastes sour
- cause indicators to change colour to red
- are corrosive
- many solutions of acids conduct electricity
- reacts with carbonates to form carbon dioxide and water
- react with some metals to form hydrogen
- react with bases to form bases
bases: characteristics
- taste bitter
- feel slippery
- cause indicators to change colour to blue
- can be corrosive
- do not react with most metals
- many solutions of bases conduct electricity
- react with acids to form water
conjugate
acid:
loss of H+
HCl -> Cl- (conjugate base)
base:
gain of H+
NH3 -> NH4+ (conjugate acid)
electrolytes
solutions of ions
strong electrolytes
def: completely ionises
strong electrolytes have all dissolved molecules ionise in solution, there are no molecules left only ions present in water
examples of strong electrolytes
all ionic compounds (what does dissolve goes into ions), if insoluble will still be a strong electrolyte but will have low conductivity
strong acids and strong bases: SA: HCl, HNO3, H2SO4, SB: group 1 and group 2 metal oxides and hydroxides
weak electrolytes
definition: partially ionises, only some dissolved molecules ionise in solution, there will be neutral molecules and some ions present in the water
examples of weak electrolytes
weak acids and bases:
WA: CH3COOH, H3PO4, H2CO3, WB: NH3
non-electrolytes
definition: doesn’t ionise, all remain as neutral species in solution
examples of non-electrolytes
most covalent substances that aren’t acids or bases e.g. sugar (C6H12O6), sucrose, kerosene and ethanol
hydronium ion
H3O+ is an ion that is formed through the protonation of water
H2O + H+(ion) → H3O+
