A solution contains Na2CO3 and NaHCO3.10 ml of the solution requires 2.5 ml of 0.1M H2SO4 for neutralisation using phenolphthalein as an indicator. Methyl orange is added when further 2.5 ml of 0.2 M H2SO4 is required. The amount of NaHCO3 in one litre of the solution is