减少的质量是水和CO2:
2NaHCO3 = Na2CO3 + H2O(g) + CO2(g)
2*84 18 + 44 = 62
a 2.74 - 2.12 = 0.62
168 :62 = a :0.62
a = 1.68 g
混合物中碳酸钠的质量:2.74-1.68 = 1.06 g