Final answer:
The statement is false because the conjugate base of a weak acid is relatively strong and can increase the pH by accepting protons from water to form hydroxide ions, making the solution more basic.
Step-by-step explanation:
The statement that an anion which is the conjugate base of a weak acid will decrease the pH is false. A weak acid has a conjugate base that is relatively strong. For example, the acetate ion, the conjugate base of the weak acid acetic acid, can accept a hydrogen ion from water, forming hydroxide ions in the process. This increase in hydroxide ion concentration results in a higher pH, meaning the solution becomes more basic, not acidic.
Moreover, the strength of an acid or base in aqueous solution is typically assessed by its acid or base ionization constants. Strong acids have very weak conjugate bases that do not affect pH significantly because they are weaker bases than water. On the other hand, weak acids, which are only partially ionized in water, have stronger conjugate bases capable of raising the pH.
Non-neutral pH readings in water arise from the dissolution of acids and bases. An acid increases the concentration of hydrogen ions, resulting in a lower pH, while a base decreases the concentration of hydrogen ions, leading to a higher pH. The pH of the solution increases when the conjugate base of a weak acid is involved because it is a stronger base that will accept protons from water, forming hydroxide ions.