Phosphoric Acid Equilibrium: Unraveling the Chemistry Behind It
What happens when phosphoric acid dissolves in water?
When phosphoric acid (H₃PO₄) dissolves in water, what equilibrium is established?
Which statement concerning an aqueous solution of phosphoric acid is correct?
A. An aqueous solution of phosphoric acid contains mainly H₃PO₄ molecules.
B. An aqueous solution of phosphoric acid contains predominantly H₃O⁺ and H₂PO₄⁻ ions.
C. An aqueous solution of phosphoric acid contains equal amounts of H₃O⁺ and H₃PO₄.
D. An aqueous solution of phosphoric acid contains a greater concentration of dissolved ions than it does neutral phosphoric acid molecules.
Answer:
The solution of phosphoric acid in water contains more undissociated H3PO4 molecules than ions due to a small Ka value of 7.5 x 10^-3. Thus, option A is correct.
Phosphoric acid (H₃PO₄) is a key player in various chemical processes and plays a crucial role in many industries. When this acid is dissolved in water, a complex equilibrium is established, involving the dissociation of H₃PO₄ into ions such as H₃O⁺ and H₂PO₄⁻.
The acid dissociation constant, Ka, for H₃PO₄ is 7.5 × 10⁻³, indicating that the dissociation is not complete. This means that the solution predominantly contains undissociated H₃PO₄ molecules rather than ions. Therefore, an aqueous solution of phosphoric acid mainly consists of H₃PO₄ molecules, supporting option A as the correct statement.
Understanding the equilibrium and chemistry behind phosphoric acid dissolution sheds light on the behavior of this important acid in aqueous solutions and its applications in various processes.