posted by mark .
thanks for the last help, i got the right answer!!
i got this wrong... (answer is supposed to be 0.165 but i put 0.0652)
A sample of Na2CO3 weighing 0.2863 g is dissolved in 50 mL of water and an endpoint is reached when 32.83 mL of HClO4 has been added. Calculate the molarity of the HClO4 solution.
ah please ignore, i got it!!