Цепочки превращения:

1) NaOH = > NaHS = > Na₂S

2) MgCl₂ = > MgOHCl = > MgCl₂

3) C = > CO₂ = > CaCO₃ = > Ca (HCO₃) ₂

4) Fe = > FeO = > FeSO₄ = > Fe (OH) ₂ = > FeO

1)

NaOH + H2S = NaHS + H2O

NaHS + NaOH (конц) = Na2S + H2O

2)

MgCl2 + KOH = MgOHCl + KCl

MgOHCl + HCl = MgCl2 + H2O

3)

C + O2 = CO2

CO2 + CaO = CaCO3

CaCO3 + CO2 + H2O = Ca (HCO3) 2

4)

2Fe + O2 = 2FeO (t = 1200-1300 градусов Цельсия)

FeO + H2SO4 = FeSO4 + H2O

FeSO4 + 2NaOH = Fe (OH) 2 + Na2SO4

Fe (OH) 2 = FeO + H2O (t=200C, атмосфера N2).