The pKa of acetic acid, HC2H3O2, is 4.76. A buffer solution was made using an unspecified amount of acetic acid and 0.30 mol of NaC2H3O2 in enough water to make 1.50 L of solution. Its pH was measured as 4.50 on a meter. How many moles of HC2H3O2 were used?
0.31 mol
0.55 mol
0.61 mol
1.09 mol
1.21 mol