A buffer is prepared by mixing 0.200 L of 0.20 M CH₃COOH and 0.200 L of 0.20 M CH₃COO⁻. After 0.020 mol of HCl(g) is bubbled into the solution and allowed to react completely, how many moles of CH₃COO⁻ remain in the solution?
a) 0.040 mol
b) 0.000 mol
c) 0.020 mol
d) 0.030 mol