Write down the reaction equations: Ca⇒CaO⇒CaCl₂⇒Ca (OH) ₂⇒CaSO₄

When writing reactions, do not forget that they must correspond to the conditions for the reaction (during the reaction, as one of its products, a gas, precipitate or water must form). Based on this rule, we get:

1) Ca + O2 = CaO;

2) CaO + HCl = CaCl2 + H2O;

3) CaCl2 + 2NaOH = Ca (OH) 2 + NaCl2 (Ca (OH) 2, although slightly soluble, is still a precipitate);

4) Ca (OH) 2 + H2SO4 = CaSO4 + 2H2O (the usual neutralization reaction, during which water is always formed as a weak electrolyte, which corresponds to the reaction conditions).