Ca → CaO → Ca(OH)₂ → Ca₃(PO₄)₂.2Ca + O₂= 2CaO  CaO  + H₂O= Ca(OH)₂3Ca(OH)₂ + 2H₃PO₄= Ca₃(PO₄)₂+ 6H₂O
Cu → CuO → CuCl2 → Cu (OH)2 → CuO → Cu.
2Cu  + O₂= 2CuO
CuO + 2HCI= CuCl₂ + H₂O
CuCl₂ + 2NaOH= Cu(OH)₂ + 2NaCI
Cu(OH)₂ +t = CuO +H₂O
CuO  + H₂ = Cu + H₂O
P → P₂O₅ → H₃PO₄ → Ca₃(PO₄)₂4P + 5O₂ = 2P₂O₅
P₂O₅ + 3H₂O= 2H₃PO₄ 
2H₃PO₄  + 3Ca(OH)₂= Ca₃(PO₄)₂ + 6H₂O

Si → SiO₂ → Na₂SiO₃ → H₂SiO₃ →  SiO₂ → Si.Si + O₂= SiO₂ 
SiO₂ + Na₂O= Na₂SiO₃
Na₂SiO₃ +2HCI = H₂SiO₃ +2NaCI
H₂SiO₃ +t  =  SiO₂ + H₂O
SiO₂ + 2Mg = Si +2 MgO