Citric acid (H3C6H5O7) is a weak polyprotic acid commonly found in citrus fruits like oranges and lemons. When citric acid is dissolved in water, it undergoes a reaction to form its conjugate base and hydronium ions.
The reaction can be represented as follows:
H3C6H5O7 (aq) + H2O (l) → H2C6H5O7⁻ (aq) + H3O+ (aq)
In this reaction, citric acid donates a proton (H+) to water, forming the conjugate base H2C6H5O7⁻ and hydronium ions, which makes the solution acidic. The equilibrium constant (Ka) for this reaction is 7.4 x 10-4, indicating that citric acid is indeed a weak acid, as not all the acid dissociates in solution.