How Does Phosphoric Acid Dissociate In Water? - Chemistry For Everyone

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Transcript

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How does phosphoric acid dissociate in water? Have you ever wondered how phosphoric acid behaves when it meets water?

This fascinating process reveals a lot about its properties and applications, especially in materials

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science and corrosion resistance. Phosphoric acid is a tropotic acid, meaning it can releases three protons when dissolved in water.

Let's break down this process step by step. When phosphoric acid dissolves in water, it

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partially ionizes. This means it loses one proton and forms the dihydrogen phosphate ion and a hydrronium ion.

The reaction looks like this. Phosphoric acid plus water equals dihydrogen phosphate ion plus hydrronium ion.

This

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first step is the strongest of the three dissociation steps, but it is still considered a weak acid because it does not fully dissociate. Instead, an equilibrium exists between the undissociated acid and the ions in the solution.

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Moving on to the second step, the dihydrogen phosphate ion can lose another proton. This forms the hydrogen phosphate ion.

In this case, the reaction is dihydrogen phosphate ion equals hydrogen phosphate ion plus hydrogen ion. This step is weaker than

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the first, meaning fewer ions dissociate. At this stage, the equilibrium shifts more toward the undissociated form.

Finally, we reach the third step. The hydrogen phosphate ion can lose its less proton to form the phosphate ion.

This

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reaction is hydrogen phosphate ion equals phosphate ion plus hydrogen ion. This step has the weakest acid strength and the least extent of dissociation.

Because phosphoric acid is a weak acid, none of these steps go to completion.

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Instead, they establish equilibria in the solution. The acid dissociation constants decrease with each proton lost, showing a decreasing tendency to lose additional protons.

Understanding this step-wise dissociation is important in chemistry

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education. It influences the pH and buffering capacity of solutions containing phosphates.

The presence of multiple dissociation equilibria allows phosphate systems to act as effective buffers across various pH levels.

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In material science, phosphoric acids partial dissociation and the resulting phosphate ions interact with metal surfaces. These phosphate ions can form protective layers on metals which helps reduce corrosion.

This barrier inhibits

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further oxidation of the metal making phosphoric acid useful in various applications. So phosphoric acid dissociates in water through three sequential steps producing different phosphate ions.

Each step is characterized by decreasing acid

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strength and establishes equilibria rather than complete ionization. This behavior is essential for its chemical properties and practical applications especially in corrosion resistance.