The pH of a solution is 6.0. Explain how the addition of the following substance would alter (or not alter) the pH of the solution.
a. HCl
b. NaOH
c. H20
Adding acid will make it more acid; pH will go down.
Adding base will make the solution more basic; pH will go up.
Adding water will make the solution more dilute and it will change the pH somewhat (a little more basic making pH go up); how much depends upon how much water is added and the identity of the solution.
To determine how the addition of a substance would alter the pH of a solution, we need to understand the effect of that substance on the concentration of hydrogen ions (H+) in the solution.
a. HCl: When hydrochloric acid (HCl) is added to a solution, it dissociates into H+ ions and chloride (Cl-) ions. Since H+ ions increase the concentration of hydrogen ions in the solution, adding HCl would decrease the pH of the solution, making it more acidic.
b. NaOH: Sodium hydroxide (NaOH) is a strong base. It dissociates in water to produce hydroxide (OH-) ions and sodium (Na+) ions. The hydroxide ions react with hydrogen ions (H+) in the solution, reducing their concentration. This process increases the concentration of hydroxide ions in the solution relative to the hydrogen ions, which results in an increase in pH, making the solution more basic or alkaline.
c. H2O: Water (H2O) is neutral and has a pH of 7.0. Adding pure water to a solution would not alter its pH because water does not contain any additional hydrogen or hydroxide ions.