Carbonate buffering in natural waters involves the conjugate pairs H CO /HCO and HCO /CO
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
Carbonate buffering in natural waters involves the conjugate pairs H2CO3/HCO3− and HCO3−/CO32−. A 1.00 L sample of water contains 0.20 mol of H2CO3 and 0.20 mol of HCO3−.
A field scientist first adds 0.010 mol of solid NaOH to the water sample, allows the system to reach equilibrium, and then subsequently adds 0.010 mol of gaseous HCl (assume complete dissolution and ionization).
(a) Write the balanced net ionic equation that represents the reaction occurring immediately after the NaOH dissolves in the buffered water.
(b) After the reaction in part (a) has gone to completion, write the balanced net ionic equation for the reaction that occurs when HCl is introduced.
(c) Using the equations from parts (a) and (b), construct a sequence of reactions (with stoichiometric coefficients) showing how the system cycles between conjugate pairs to resist large pH changes despite the sequential additions.
(d) Discuss how the order of addition (base first, then acid) influences which species act as the conjugate acid and conjugate base in each step.