Question

For each of the substances in below classify it as a strong or weak electrolyte and state whether it exists in solution as molecules, ions, or a mixture of both molecules and ions.

a) hypochlorous acid

      b) strontium hydroxide

      c) perchloric acid

      d) butanoic acid

Answer 1

   a) hypochlorous acid is weak electrolyte

      b) strontium hydroxide is strong electrolyte

      c) perchloric acid is stong electrolyte

      d) butanoic acid is weak electrolyte

Strong electrolytes completely ionize in water. This means 100% of the dissolved chemical breaks into cations and anions. However, it does not mean the chemical completely dissolves in water! For example, some species are only slightly soluble in water, yet are strong electrolytes. This means that not very much dissolves, but all that does dissolve breaks into ions. An example is the strong base strontium hydroxide, Sr(OH)2. It has a low solubility in water, but dissociates completely into Sr2+ and OH– ions. While a flask of sodium hydroxide (NaOH) in water would contain Na+ and OH– ions in water, but no actual NaOH, a flask of aqueous strontium hydroxide would contain Sr2+ and OH– ions, Sr(OH)2, and water.

Weak electrolytes partially ionize in water. Pretty much any dissociation into ions between 0% and 100% makes a chemical a weak electrolyte, but in practice, around 1% to 10% of a weak electrolyte breaks into ions.