Acids react with carbonates to form a salt, water and carbon dioxide. For example, calcium carbonate with hydrochloric acid: CaCO3 + 2HCl → CaCl2 + H2O + CO2. The carbon dioxide makes the mixture fizz, and it turns limewater milky.
Some metals react with acids to form a salt and hydrogen. Magnesium with hydrochloric acid: Mg + 2HCl → MgCl2 + H2. Zinc with sulfuric acid: Zn + H2SO4 → ZnSO4 + H2. Hydrogen is tested with a lit splint, which gives a squeaky pop. Only some metals react: copper, low in the reactivity series, does not react with dilute acids.
Equations must balance, with the same number of each type of atom on both sides. In the magnesium equation there are two chlorine atoms in MgCl2, so two HCl are needed on the left. The salt name comes from the metal or carbonate and the acid, for example magnesium chloride or zinc sulfate.