Вариант 3.
1) Ca → CaO → Ca(OH)₂ → CaCO₃.
2Ca + O₂ = 2CaO.
CaO + H₂O = Ca(OH)₂.
Ca(OH)₂ + CO = CaCO₃ + H₂.
2) As → As₂O₅ → H₃AsO₄ → Na₃AsO₄.
4As + 5O₂ = 2As₂O₅.
As₂O₅ + 3H₂O = 2H₃AsO₄.
H₂AsO₄ + 3NaOH = Na₃AsO₄ + 3H₂O.
3) Fe → Fe₂O₃ → FeCl₃ → Fe(OH)₃ → Fe(NO₃)₃.
4Fe + 3O₂ = 2Fe₂O₃.
Fe₂O₃ + 6HCl = 2FeCl₃ + 3H₂O.
FeCl₃ + 3NaOH = Fe(OH)₃ + 3NaCl.
Fe(OH)₃ + 3HNO₃ = Fe(NO₃)₃ + 3H₂O.
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Вариант 4.
1) Ba → BaO → Ba(OH)₂ → Ba(NO₃)₂.
2Ba + O₂ = 2BaO.
BaO + H₂O = Ba(OH)₂
Ba(OH)₂ + 2HNO₃ = Ba(NO₃)₂ + 2H₂O.
2) S → SO₂ → H₂SO₃ → Na₂SO₃.
S + O₂ = SO₂.
SO₂ + H₂O = H₂SO₃.
H₂SO₃ + 2NaOH = Na₂SO₃ + 2H₂O.
3) Al → Al₂O₃ → AlCl₃ → Al(OH)₃ → Al₂(SO₄)₃.
4Al + 3O₂ = 2Al₂O₃.
Al₂O₃ + 6HCl = 2AlCl₃ + 3H₂O.
AlCl₃ + 3H₂O = Al(OH)₃ + 3HCl.
2Al(OH)₃ + 3H₂SO₄ = Al₂(SO₄)₃ + 6H₂O.