Tips for Understanding Phosphoric Acid Equilibrium
What is the state of the solution?
As Ka increases, the concentration of products relative to the reactant also increases. Conversely, when Ka is small, it means that the reaction favors the formation of the reactant over the products.
Given that Ka is relatively small (7.5 x 10^-3), it indicates that the equilibrium position of this reaction lies more to the left, favoring the formation of the undissociated acid over the products.
Option A
An aqueous solution of phosphoric acid contains mainly H3PO4 molecules.
Phosphoric acid (H3PO4) forms an equilibrium in water according to the reaction: H3PO4 + H2O ⟷ H3O+ + H2PO4-. When Ka = 7.5 x 10^-3 for H3PO4, the equation shows that the majority of the phosphoric acid molecules remain undissociated in the solution, making the solution primarily consist of H3PO4 molecules.
Understanding the state of the solution in relation to the equilibrium constant Ka can provide insights into the behavior of phosphoric acid in aqueous solutions. With a relatively small Ka value, the equilibrium position favors the undissociated acid, leading to the predominance of H3PO4 molecules in the solution. This knowledge is crucial for grasping the properties and characteristics of phosphoric acid solutions, highlighting the importance of equilibrium constants in determining the composition of chemical systems.