The relationship [H+] = 10^-pH expresses the connection between hydrogen ion concentration and pH.

The relationship [H+] = 10^-pH expresses the connection between hydrogen ion concentration and pH.

• A. True
• B. False
• C. Only for solutions with acids
• D. Only at 25°C

Answer: (B)

pH is defined as the negative logarithm of the hydrogen ion activity in solution, pH = -log a_H+. The exact link between hydrogen ion concentration [H+] and pH uses the activity, not just concentration. While in very dilute solutions at standard temperature (about 25°C) the activity approximates the concentration, so [H+] ≈ 10^-pH, this is only an approximation. In general, factors like temperature and ionic strength change activity coefficients, so pH = -log a_H+ and [H+] = 10^-pH is not strictly true under all conditions.

pH is defined as the negative logarithm of the hydrogen ion activity in solution, pH = -log a_H+. The exact link between hydrogen ion concentration [H+] and pH uses the activity, not just concentration. While in very dilute solutions at standard temperature (about 25°C) the activity approximates the concentration, so [H+] ≈ 10^-pH, this is only an approximation. In general, factors like temperature and ionic strength change activity coefficients, so pH = -log a_H+ and [H+] = 10^-pH is not strictly true under all conditions.