CHEM 162: Buffer Calculations page 1 of 4 CHEM 162 Buffer Calculations Part I Ex. 1: Consider a solution of 0.50 mol NH3 and 0.50 mol NH4Cl in 1.00 L of solution. a. Calculate the pH of the solution. (Kb=1.8×10-5 for NH3) Thus, when equal amounts of a weak acid and its conjugate base are present in solution, the pH=pKa for the solution, just like at the half-equivalence point for a weak acid – strong base titration. b. Consider when 0.05 mol of hydrochloric acid is added to the solution described above. Draw the substances indicated in the beakers below: + → NH3(aq) + NH4Cl(aq) HCl(aq) after mixing c. Calculate the concentration of the major species that influence pH before and after the reaction based on the limiting reagent. NH3(aq) + H+(aq) → NH4+ Before reaction After reactionCHEM 162: Buffer Calculations page 2 of 4 d. Finally, calculate the pH when 0.05 mol of hydrochloric acid is added to the solution of 0.50 mol NH3 and 0.50 mol NH4Cl in 1.00 L of solution. The pH of the NH3/NH4+ solution was initially ____________________. The pH after adding the 0.05 mol of HCl to the NH3/NH4+ solution was _______________. e. Calculate the pH of a resulting solution when 0.05 mol of HCl is added to 1.00 L DI water. f. Compare how the pH changes upon addition of the small amount of HCl to the buffer solution with how the pH changes upon addition of the small amount of HCl to the DI water?CHEM 162: Buffer Calculations page 3 of 4 g. Consider when 0.05 mol of sodium hydroxide is added to 0.50 mol NH3 and 0.50 mol NH4Cl in 1.00 L of solution. Draw the substances indicated in the beakers below: + → NH3(aq) + NH4Cl(aq) NaOH(aq) after mixing h. Calculate the concentration of the major species that influence pH before and after the reaction based on the limiting reagent. NH4+(aq) + OH−(aq) → H2O(l) + NH3(aq) Before reaction After reaction i. Finally, calculate the pH when 0.05 mol of sodium hydroxide is added to a solution of 0.50 mol NH3 and 0.50 mol NH4Cl in 1.00 L of solution.CHEM 162: Buffer Calculations page 4 of 4 j. Fill in the blanks below: The pH of the NH3/NH4+ solution was initially ____________________. The pH after adding the 0.05 mol of NaOH to the NH3/NH4+ solution was _______________. k. Calculate the pH of a resulting solution when 0.05 mol of NaOH is added to 1.00 L DI water. l. Compare how the pH changes when a small amount of NaOH is added to the buffer solution compared to how pH changes when a small amount of NaOH is added to DI