<span>The reason it will be 7 for some titrations is that when you titrates a strong acid with a strong base for example HCl and NaOH the salt formed is conjugate base of strong acid and will be a very weak base That means that it cannot produce any OH^-1 and all the H+ has been converted to water.The only source of H+ or OH is water with a Ka of 10^-14 so the pH = -log [H+]=-log 10^-7 = 7 second reason is When you titrates a weak acid with strong base at equivalence point only a water solution of the conjugate base exists
CH3COOH + NaOH ----- Na+ CH3COO^-1 + H2O Since the conjugate base is the conjugate base of a weak acid it will hydrolyze in water like so for instance Na+ CH3COO^-1 + HCl---- CH3COOH + NaCl the equivalence point will be way BELOW 7 and in the case of above will be less than 5. So pH of 7 at equivalence point is only reached in strong acid strong base titrations. hope this helps</span>
PH is 7 in case the strength of the acid and base are the same ( i.e. either weak or strong). In case of strong acid weak base or weak acid strong base titrations, buffer solutions can be formed which result in a pH other than 7
The reaction equation given is already balanced. So the ratio of the reactants and products is the same as the ratio of coefficients. Then the answer is 4 moles.
