In aqueous solutions, what does pH measure?

• A. The total amount of dissolved salts (ionic strength) in the solution
• B. The temperature of the solution in degrees Celsius
• C. The hydrogen ion concentration in solution, expressed as $pH=-\log \left(H_3{O}^{+}\right)$
• D. The concentration of hydroxide ions, $[O^H-]$, only

Answer: (C)

Verified step by step guidance

1. Understand that pH is a measure of the acidity or basicity of an aqueous solution, which relates to the concentration of hydrogen ions (more precisely, hydronium ions, H\_3O\^+) present in the solution.
2. Recall the definition of pH, which is given by the formula: \(pH = -\log([H\_3O\^+])\) This means pH is the negative logarithm (base 10) of the hydronium ion concentration.
3. Recognize that a lower pH value corresponds to a higher concentration of hydronium ions, indicating an acidic solution, while a higher pH corresponds to a lower concentration, indicating a basic or alkaline solution.
4. Note that pH does not measure the total amount of dissolved salts (ionic strength) or the temperature of the solution, nor does it directly measure hydroxide ion concentration, although pH and hydroxide ion concentration are related through the water dissociation equilibrium.
5. Summarize that pH specifically quantifies the hydrogen ion concentration in solution, making it a fundamental parameter for understanding the solution's acidity.