I think :::
1 mole of NaCO3 reacts with 2 mole of HCl
no. of mole of Na2CO3=molarity * volume(in dm3)
So that no. of mole of HCl= no. of mole of Na2CO3 * 2
volume of HCl used = no. of mole of HCl / molarity of HCl
if you used 0.1M of HCl,
then volume of HCl = 50mL
But I am not sure is this correct ^ ^"