Question

For the titration of 30.0 mL of 0.250 M NH3 with 0.500 M HCl at 25 °C, determine the relative pH at each of these points. A) before the addition of any HCl pH>7 pH<7 pH=7 B) after 15.0 mL of HCl have been added pH>7 pH<7 pH=7 C) after 35.0 mL of HCl have been added pH>7 pH<7 pH=7

Answer 1

A)

Before addition of acid (HCl) to base (NH3) solution is basic and so pH >7.

B)

At equivalence point , number of moles of HCl added is equal to the moles of NH3 present. So volume of HCl added at equivalence is

V_HCl = (V_NH3 * M_NH3) / M_HCl

= (30.0 mL) *(0.250) / 0.500

= 15 mL

That is after addition of 15 mL HCL , NH3 and HCl react completely and form NH4. So the solution will be acidic.

Thus , pH <7

C)

After addition of 35 mL HCl , that is obeyed eauivalence point , entire NH3 reacts and HCl id=s left over.So , the solution will be acidic and pH <7.