To conduct electricity, a substance must contain freely mobile, charged species. Most familiar is the conduction of electricity through metallic wires, in which case the mobile, charged entities are electrons. Solutions may also conduct electricity if they contain dissolved ions, with conductivity increasing as ion concentration increases. Applying a voltage to electrodes immersed in a solution permits assessment of the relative concentration of dissolved ions, either quantitatively, by measuring the electrical current flow, or qualitatively, by observing the brightness of a light bulb included in the circuit [link].
Ionic Electrolytes Water and other polar molecules are attracted to ions, as shown in [link]. 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.
Someone who has an electrolyte level that is too high can become overhydrated. Both situations can be dangerous; an electrolyte imbalance can keep the body from functioning as it should. An electrolyte imbalance can be caused by anything that disrupts the balance of water in the body. For example, sweating due to heavy exertion can cause electrolyte levels to become low.
This is why athletes and those who exercise vigorously can benefit from electrolyte-containing drinks, such as Gatorade and Powerade. Other common causes of electrolyte imbalance include diarrhea, vomiting, kidney function issues, and medications that cause one to retain or lose water.
The body needs a number of electrolytes. Eating foods or drinking beverages that have these substances is the primary way that people or animals take in the electrolytes they need. The electrolytes that tend to be present in the bodies of humans and animals are not the only ones that exist.
Many chemical compounds are electrolytes and can be used for a variety of purposes. Some are food additives while others are substances used in industrial applications.
Many should not be consumed or even touched directly. 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.
The water molecules play an essential part in forming ions: Solutions of hydrogen chloride in many other solvents, such as benzene, do not conduct electricity and do not contain ions. Likewise, weak acids and bases that only react partially generate relatively low concentrations of ions when dissolved in water and are classified as weak electrolytes.
The reader may wish to review the discussion of strong and weak acids provided in the earlier chapter of this text on reaction classes and stoichiometry. Substances that dissolve in water to yield ions are called electrolytes. Explain what happens when electrolytes dissolve in water. Give the equilibrium constant expression for ionizaton. Explain ion product of water, autoionization of water, and pH.
Calculate ionization percentage of weak electrolytes. Explain metathesis reactions. Electrolytes Substances that give ions when dissolved in water are called electrolytes.
Pure water is a very weak electrolyte. Electrolytes in Body Fluids Our body fluids are solutions of electrolytes and many other things.
Electrolytes and Batteries Solutions of electrolytes are always required in batteries, even in dry cells. Chemical Reactions of Electrolytes When solutions of electrolytes are combined, the cations and anions will meet each other. These are called metathesis reactons, which include: Solid formation or precipitation reactions: the cations and anions form a less soluble solid, resulting in the appearance of a precipitate.
Gas formation reactions: When neutral gaseous molecules are formed in a reaction, they leave the solution forming a gas. Do the positive ions move in the salt bridge? Hint: yes The two types of ions move in opposite directions. Which of the following will you use as the salt bridge?
A solution of which one of the following will best conduct electricity? All solutions have the same concentration in M. Which one of the following solutions has the highest pH?
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