ok, so the reaction goes like this ... M2CO3 + 2 HCl ---------- 2 MCl + H2O + CO2
we get to know that ... 1 mole of M2Co3 gives 1 mole of CO2
therefore, 0.01186mole of CO2 is produced when 0.01186 mole of M2CO3 is taken. (1)
given : 1g of m2co3
so, 1g of m2co3 has 0.01186 moles (from 1)
molar mass = 1/0.01186=84.3g mol-1