All useless answers. Shouldn't lose points if answers are not helpful...
A 0.4863-g sample of primary standard sodium carbonate (Na2CO3, fw 105.988) was treated with 40.00-mL of a dilute perchloric acid (HClO4, fw 100.458) solution. The solution of boiled to remove CO2, following which the excess HClO4 was back-titrated with 8.72-mL of 0.3045 M NaOH using bromocresol green as an indicator.
What is the concentration of the perchloric acid solution?