Calculate the pH of 100 mL of 030 M NH3 before and after the

Calculate the pH of 100 mL of 0.30 M NH3 before and after the addition of 4.0g of NH4NO3. The equation for the dissociation of NH3 is NH3(aq) + H20(l) NH4+(aq) + OH-(aq) What is the pH before the addition of NH4N03? What is the pH after addition of 4.0g of NH4NO3? Account for the change in pH.

Solution

a) Since ammonia is a strong base, it reacts completely to form ammonia ion and hydroxide ion, so the resulting hydroxide concentration is 0.3 M. the pOH is -log(0.3) = 0.523. pH = 14 - pOH so pH = 13.4771

b) the molar mass of ammonium nitrate is 80.052 g/mol --> 0.049968 mol of ammonium nitrate. Not exaclty sure how to factor this in... but it will DECREASE the pH as seen in c

c) the pH will decrease because of L\'chatlier\'s prinicple. You are adding product (ammonium ion), so that shifts the equilibrium towards the reactants. This decreases the concentration of hydroxide ion, and thus decreases the pH