pH and pOH of Strong Acids and Bases

pH and pOH of Strong Acids and Bases

pH Scale

  • The pH scale measures how acidic or basic a substance is and it ranges from 0 to 14.
  • Acids have a pH less than 7 and are found towards the 0 end of the pH scale.
  • On the other hand, Bases have a pH greater than 7 and are found towards the 14 end of the scale.
  • A substance with a pH of 7 is considered neutral – neither acidic nor basic. Pure water usually has a pH close to 7 at 25 °C.

Calculating pH

  • The pH of a solution can be calculated using the formula: pH = -log[H+], where [H+] represents the concentration of H+ ions in the solution.
  • So, lower pH value means higher concentration of H+ ions, which implies stronger acidity. Conversely, higher pH value points to lower H+ concentration, meaning the substance is more basic or alkaline.

pOH

  • The pOH of a solution, similar to pH, is a measure of the basicity of a solution. It’s calculated by the formula: pOH = -log[OH-], where [OH-] thus denotes the concentration of OH- ions.
  • A lower pOH signifies a greater concentration of OH- ions, therefore a stronger base. Conversely, a higher pOH represents weaker basic strength.

Relation between pH and pOH

  • pH and pOH are inversely related. In any aqueous solution at 25 °C, the sum of the pH and the pOH is always 14.
  • The formula can be written as: pH + pOH = 14.
  • This means if you know the pH of a solution, you can calculate its pOH, and vice versa.

Strong Acids and Bases

  • In chemistry, strong acids and bases are those that completely dissociate into their ions in water. This means they give off the maximum amount of H+ or OH- ions respectively, shifting the pH or pOH of a solution significantly.
  • Examples of strong acids include Sulfuric acid (H2SO4), Hydrochloric acid (HCl) and Nitric acid (HNO3).
  • Examples of strong bases include Sodium hydroxide (NaOH), Potassium hydroxide (KOH) and Barium hydroxide (BaOH2).

Note: Familiarity with the pH scale, understanding how to calculate pH and pOH, and recognizing the characteristics of strong acids and bases are essential to mastering acids and bases in chemistry.