Solution The line joining CH₃COOH to PO₄^3– in Table 1 is downhill, and so the reaction

`CH_3COOH + PO_4^(3-) -> CH_3COO^- + HPO_4^(2-)`

should occur. There is a further possibility because HPO₄^2– is itself a base and might accept a second proton. The line from CH₃COOH to HPO₄^2– is also downhill, but just barely, and so the reaction

`CH_3COOH + HPO_4^(2-) -> CH_3COO^- + H_2PO_4^-`

can occur, but it does not go to completion. Hence double arrows are used. Although H₂PO₄^– is a base and might be protonated to yield phosphoric acid, H₃PO₄, a line drawn from CH₃COOH to H₂PO₄^– is uphill, and so this does not happen.