Strong electrolytes completely ionize in water. 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.
Examples : Strong acids, strong bases , and salts are strong electrolytes. Weak electrolytes partially ionize in water. Examples : Weak acids and weak bases are weak electrolytes. The electrostatic attraction between an ion and a molecule with a dipole is called an ion-dipole attraction.
These attractions play an important role in the dissolution of ionic compounds in water. When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them.
This process represents a physical change known as dissociation. Under most conditions, ionic compounds will dissociate nearly completely when dissolved, and so they are classified as strong electrolytes.
Let us consider what happens at the microscopic level when we add solid KCl to water. Ion-dipole forces attract the positive hydrogen end of the polar water molecules to the negative chloride ions at the surface of the solid, and they attract the negative oxygen ends to the positive potassium ions. The reduction of the electrostatic attraction permits the independent motion of each hydrated ion in a dilute solution, resulting in an increase in the disorder of the system as the ions change from their fixed and ordered positions in the crystal to mobile and much more disordered states in solution.
This increased disorder is responsible for the dissolution of many ionic compounds, including KCl, which dissolve with absorption of heat. In other cases, the electrostatic attractions between the ions in a crystal are so large, or the ion-dipole attractive forces between the ions and water molecules are so weak, that the increase in disorder cannot compensate for the energy required to separate the ions, and the crystal is insoluble. Such is the case for compounds such as calcium carbonate limestone , calcium phosphate the inorganic component of bone , and iron oxide rust.
Water ionizes when one molecule of water gives up a proton to another molecule of water, yielding hydronium and hydroxide ions. In some cases, we find that solutions prepared from covalent compounds conduct electricity because the solute molecules react chemically with the solvent to produce ions. For example, pure hydrogen chloride is a gas consisting of covalent HCl molecules. This gas contains no ions. However, when we dissolve hydrogen chloride in water, we find that the solution is a very good conductor.
Skip to main content. Search for:. Define weak electrolyte. Explain how to write equations for a weak electrolyte in solution. Can car batteries be hazardous? Summary A strong electrolyte exists mainly as ions in solution.
A weak electrolyte has only a small amount of ionization in solution. What is the principle species for a weak electrolyte? Is KOH a strong electrolyte or a weak electrolyte? How would you classify CaCl 2? Review Is gaseous HCl an electrolyte or a nonelectrolyte?
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