Chemistry
Chemistry
Problem
A chemist mixes 50.0 mL of 0.25 M NH₃(aq) with 30.0 mL of 0.25 M HCl(aq). Assume volumes are additive and temperature is 25 °C. The base-dissociation constant for NH₃ is K_b = 1.8 × 10⁻⁵. (a) Calculate the number of moles of each species present immediately after mixing but before any acid–base reaction occurs. (b) Determine whether the final solution is a buffer. Support your answer with quantitative evidence based on the stoichiometry of the neutralization reaction. (c) If the solution is a buffer, calculate its pH. If it is not a buffer, calculate the pH that results from the dominant species present.Intuitive explanation
This is an acid–base neutralization problem where you need to recognize that HCl (strong acid) will react completely with NH₃ (weak base) to form NH₄⁺, leaving you with a buffer or excess reactant. Calculate moles of each reactant, identify the limiting reagent, then determine what species remain in solution—this tells you whether you have excess base, excess acid, or a buffer system that requires equilibrium analysis.
Intuitive explanation
This is an acid–base neutralization problem where you need to recognize that HCl (strong acid) will react completely with NH₃ (weak base) to form NH₄⁺, leaving you with a buffer or excess reactant. Calculate moles of each reactant, identify the limiting reagent, then determine what species remain in solution—this tells you whether you have excess base, excess acid, or a buffer system that requires equilibrium analysis.