pH = -log[H+]
Lower pH values indicate higher concentrations of hydrogen ions, whereas higher pH values indicate lower concentrations of hydrogen ions.
In the case of acidic substances, they contain more hydrogen ions compared to basic substances. When an acid is dissolved in water, it undergoes ionization, releasing H+ ions. This increase in the number of H+ ions in the solution leads to a lower pH value.
For example, when hydrochloric acid (HCl) is dissolved in water, it dissociates into H+ and Cl- ions:
HCl → H+ + Cl-
The higher the concentration of HCl, the more H+ ions are released, resulting in a lower pH value.
On the other hand, basic substances, also known as alkalis, have a higher concentration of hydroxide ions (OH-) compared to hydrogen ions. When a base is dissolved in water, it also undergoes ionization, releasing OH- ions. The higher concentration of OH- ions leads to a lower concentration of H+ ions, resulting in a higher pH value.
For example, when sodium hydroxide (NaOH) is dissolved in water, it dissociates into Na+ and OH- ions:
NaOH → Na+ + OH-
The higher the concentration of NaOH, the more OH- ions are released, resulting in a higher pH value.
In summary, acidic substances have a lower pH value than basic substances due to the higher concentration of hydrogen ions present in acidic solutions.
