The mass of sodium carbonate required to prepare 250ml of 0.4N solution is

Answer 1

Technically, one can't calculate this BECAUSE there is no reaction given; however, we usually assume, when the reaction isn't given, to use total + or - charge. That is 2 in this case; therefore,
mL x N x mew = grams where mew is milliequivalent weight.
equivalent weight then is molar mass/2 = 106/2 = 53 and mew is 0.053.Substitute mL, N, mew and solve for grams.