1 a KHP Potassium hydrogen phthalate is used as our primary

1.

a. KHP (Potassium hydrogen phthalate) is used as our primary standard. What is meant by a primary standard? Why are we using KHP specifically?

b. What are the balanced chemical reactions taking place for each titration (NaOH+KHP & HCl+NaOH)?

Solution

1)A primary standard is a particular substance which is stable towards heat(i,e; towards decomposition) and is non hygroscopic(does not soak moisture from atmosphere).That implies a primary standard\'s wight remains intact for long time.

Solid NaOH is highly hygroscopic (it absorbs water from the air) and thus it cannot be accurately weighed.A KHP sample of known mass (and, therefore, known moles) can be titrated with the NaOH solution to determine very precisely the concentration of the NaOH.

2) KHS(C₈H₅KO₄)(aq)+NaOH(aq)=C₈H₅KNaO₄(salt)+H₂O(l)

HCl(aq)+NaOH(aq)=NaCi(salt)+H₂O(l)