H2SO4+CaCl2=CaSO4+2HCl Why does sulfuric acid produce hydrochloric acid if sulfuric acid is a stronger acid than HCl? Answer with details, please.

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t-nez eNotes educator| Certified Educator

You're correct that sulfuric acid and hydrochloric acid (HCl) are both strong acids. This means that they are completely ionized in water. Calcium chloride is soluble in water but calcium sulfate is not. When an aqueous solution of calcium chloride is combined with aqueous sulfuric acid, the calcium ions and sulfate ions combine to precipitate insoluble calcium sulfate:

`H_2SO_4_(aq) + CaCl_2_(aq) -> 2 HCl__(aq) + CaSO_4_(s)`

Hydrogen chloride isn't actually produced, the ions H+ and Cl- remain in solution as spectator ions. Spectator ions exist as both reactants and products and aren't part of any precipitate that forms so they cancel out in the net ionic equation:

`Ca^(2+)_(aq)+ SO_4^(2-) _(aq) -> CaSO_4_(s)`

Calcium sulfate, which is also called gypsum, is formed as the hydrate `CaSO_4*2H_2O`

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