Final answer:
True, a low pH means a high concentration of hydrogen ions ([H+]). The pH scale is logarithmic, so each descending unit indicates a tenfold increase in [H+].
Step-by-step explanation:
The statement is true; a low pH indeed means a high concentration of hydrogen ions ([H+]). The pH scale is logarithmic, meaning each whole pH value below 7 is ten times more acidic than the next higher value. Therefore, lower pH numbers correspond to higher acidity, which implies greater amounts of hydrogen ions in the solution. For instance, a solution with a pH of 4 has ten times more hydrogen ions than a solution with a pH of 5.
Acids are substances that contribute hydrogen ions to the solution and thus lower the pH. The more hydrogen ions provided by an acid, the lower the pH will become, indicating a more acidic environment. Conversely, bases provide hydroxide ions (OH-) or other negatively charged ions that bind with hydrogen ions, reducing their concentration, and as a result, increasing the pH of the solution. When bases release hydroxide ions, these ions react with free hydrogen ions to create water molecules, thus removing hydrogen ions from the solution and raising the pH.
The relationship between pH and hydrogen ions is summed up simply: pH is inversely related to the [H+]. A change in pH of one unit reflects a tenfold change in hydrogen ion concentration. Thus, highly acidic solutions have low pH values and high hydrogen ion concentrations.