A buffer solution is prepared by mixing 200 mL of 0.50 M NH₃ with 100 mL of 0.50 M…
CHEMISTRY · Single correct · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A buffer solution is prepared by mixing 200 mL of 0.50 M NH₃ with 100 mL of 0.50 M NH₄Cl and diluting the mixture to 500 mL. A chemist then adds 15.0 mL of 0.20 M HCl to the buffer. Neglecting volume change for the titrant, which statement most accurately describes the resulting pH change?
(a) The pH decreases significantly because the strong acid converts most of the NH₃ into NH₄⁺, nearly exhausting the buffer.
(b) The pH decreases slightly because NH₃ is in excess and will partially neutralize the added HCl without exhausting the buffer.
(c) The pH increases slightly because dilution by the added HCl solution lowers the overall concentration of hydrogen ions more than the reaction produces them.
(d) The pH increases because the added HCl reacts primarily with NH₄⁺, shifting the equilibrium to consume H⁺ and produce more NH₃.