Write the chemical equation showing dihydrogen phosphate and hydrogen phosphate conjugate acid-base relationship. Identify the acid and base. Explain how the equilibrium is shifted as buffer reacts with an acid and reacts with a base.

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The chemical equation showing the dihydrogen phosphate and hydrogen phosphate conjugate acid-base relationship can be represented as follows:

H2PO4^- (dihydrogen phosphate) + H2O ⇌ H3O+ + HPO4^2- (hydrogen phosphate)

In this equation, dihydrogen phosphate (H2PO4^-) acts as an acid as it donates a proton (H+) to water, forming hydronium ion (H3O+). The resulting ion, hydrogen phosphate (HPO4^2-), acts as a base as it accepts the proton from water.

When a dihydrogen phosphate and hydrogen phosphate buffer reacts with an acid, the equilibrium is shifted to the left, favoring the formation of more dihydrogen phosphate. This happens because the added acid increases the concentration of H3O+ ions in the solution. As a result, the excess H3O+ ions react with the hydrogen phosphate ion (HPO4^2-) to form more dihydrogen phosphate (H2PO4^-), according to Le Chatelier's principle, which states that a system will shift in a direction that minimizes the effect of the imposed change. Therefore, the equilibrium will shift to the left to consume the excess H3O+ ions by forming more dihydrogen phosphate.

On the other hand, when the buffer reacts with a base, the equilibrium is shifted to the right, favoring the formation of more hydrogen phosphate. This occurs because the added base reacts with the excess H3O+ ions in the solution, consuming them. As a result, the equilibrium shifts to the right to restore the balance, leading to the formation of more hydrogen phosphate ions (HPO4^2-).

Overall, the buffer system helps maintain a stable pH by resisting changes in acidity or alkalinity when small amounts of acid or base are added. By having both the conjugate acid (dihydrogen phosphate) and base (hydrogen phosphate) present, the buffer can react in either direction to maintain the equilibrium and the desired pH.