Topic 12- acid based equilibrium

Example of a strong acid

HCl, H2SO4, HNO3.

HCl (reversible sign) H+ + Cl-.

Forwards reaction favoured strongly. Lots of H+ produced

Example of a strong base

NaOH, KOH.

NaOH (reversible sign) Na+ + OH-.

Forward reaction favoured strongly. Lots of OH- produced

Example of a weak base

NH3.

NH3 + H2O (reversible sign) NH4+ + OH-.

Backwards reaction favoured so not any OH- ions produced

Example of strong base

KaOH, KOH.

Forward reaction favoured strongly. Lots of OH- produced

What are conjugate pairs

They are linked by a transfer of a proton.

Any species that has gained a proton is the conjugate acid, any species that has lost a proton is the conjugate base.

How can ammonia act as a base

Ammonia doesn’t produce OH- directly. It reacts with water first and accepts a proton to produce ammonium ions and OH- ions.

NH3 + H2O (reversible sign) NH4+ + OH-

Standard enthalpy change of neutralisation

The enthalpy change when an acid and base react together under standard conditions in their standard states to produce one mole of water.

Is always exothermic (-deltaH)

What happens in the enthalpy of neutralisation of weak acids and bases

They partially dissociate so the H+ and OH- are used up quickly in a neutralisation reaction as there are only a small number in solution.

Therefore the acid and base are constantly dissociating to replace the H+ and OH- that have reacted.

There are 2 types of enthalpy involved in neutralisation: enthalpy of dissociation, enthalpy when OH- and H+ react.

Enthalpy of dissociation varies depending in the acid or base being used. So enthalpy of neutralisation varies too

what happens in enthalpy of neutralisation of strong acids and bases

these dissociate fully to produce OH- and H+ in solution.

There is only one type of enthalpy involved: enthalpy when OH- and H+ react. There’s no enthalpy of dissociation as they dully dissociate

what is pH

a logarithmic scale that measures the concentration of H+ ions in solution

whats the equation for pH

pH = -log10 [H+]