An acid salt is a salt of an acid that has two or more replaceable hydrogen atoms in which not all of the hydrogens are replaced by a metal or its equivalent. For example, the dibasic acid carbonic acid (H₂CO₃) forms acid salts such as sodium hydrogen carbonate (sodium bicarbonate, NaHCO₃). The tribasic acid phosphoric (V) acid (orthophosphoric acid, H₃PO₄) forms two series of acid salts, such as sodium dihydrogen phosphate (NaH₂PO₄) and disodium hydrogen phosphate (Na₂HPO₄).