Reactivity 3.1 – Proton transfer reactions

3.1.4 – The pH scale

📌 What is pH?

  • The pH (potential of hydrogen) scale is the scale used to measure how acidic or how basic a certain substance is
  • The scale ranges from 0 to 14, with 0 being the most acidic, 14 being the most basic and 7 being perfectly neutral
  • The pH of a certain solution is determined by the concentration of hydrogen ions present in the solution
  • The pH scale is the logarithmic expression of this concentration

Formula for calculating pH :

pH = -log10[H+] where H+is the concentration of hydrogen ions in a solution

  • Some features of the pH scale include :
  1. pH does not have units
  2. The pH of a substance is inversely related to the hydrogen ion concentration (ie greater pH means lower concentration)
  3. Increasing or decreasing the pH by 1 unit on the pH scale represents a 10x change in the concentration of hydrogen ions (due to logarithmic properties)
  • The concentration of hydrogen ions is inverse to the concentration of hydroxide ions present in any aqueous solution, thus making the pH scale measurement a suitable way to test BOTH acidity and alkalinity