These unique salts still contain at least one hidden hydrogen atom from their parent acid. When you drop this specific salt into regular water, it breaks apart into floating ions. The negatively charged ion still firmly holds onto a spare hydrogen atom.
This special negatively charged ion acts like a weak acid all by itself. It releases its extra hydrogen atom into the surrounding water as a positive proton. These extra floating protons are exactly what makes any chemical liquid truly acidic.
These salts show us that neutralization reactions do not always create a neutral mixture. The reaction can easily stop exactly halfway, leaving an unbalanced chemical product behind. A common student mistake is assuming all salts are perfectly neutral like regular table salt.
The final pH of any salt water depends heavily on its original parent chemicals. If the parent strong acid beats the parent weak base, the final salt becomes acidic. Acidic salts are extremely common in large industrial food processing factories.
Commercial bakers use them constantly in special baking powders to help fluffy cakes rise. Plumbers also use them in harsh chemical cleaners to dissolve tough mineral pipe clogs.