Medicinal Chemistry lectures by Asist.Prof.Dr.Alaa J.Mahrath

Types of Electrolytes :Electrolytes can be further classified as strong electrolytes or weak electrolytes. For a strong electrolyte, such as sodium chloride (NaCl), there is 100% dissociation of the solute into ions. When the electrodes from the light bulb apparatus are placed in the NaCl solution, the light bulb glows very brightly.In an equation for dissociation of a compound in water, the charges must balance. For example, magnesium nitrate dissociates to give one magnesium ion for every two nitrate ions. However, only the ionic bonds between Mg2+

and NO3- are broken, not the covalent bonds within the polyatomic ion. The equation for the dissociation of Mg(NO3)2 is written as follows:

A weak electrolyte is a compound that dissolves in water mostly as molecules. Only a few of the dissolved solute molecules undergo ionization, producing a small number of ions in solution. Thus solutions of weak electrolytes do not conduct electrical current as well as solutions of strong electrolytes. When the electrodes are placed in a solution of a weak electrolyte, the glow of the light bulb is very dim. In an aqueous solution of the weak electrolyte HF, a few HF molecules ionize to produce H+ and F- ions. As more H+ and F- ions form, some recombine to give HF molecules. These forward and reverse reactions of molecules to ions and back again are indicated by two arrows between reactant and products that point in opposite directions:

A nonelectrolyte such as sucrose 1sugar2 dissolves in water only as molecules, which do not ionize. When electrodes of the light bulb apparatus are placed in a solution of a nonelectrolyte, the light bulb does not glow, because the solution does not contain ions and cannot conduct electricity.

Table 9.4: summarizes the classification of solutes in aqueous solutions.

Equivalents Body fluids contain a mixture of electrolytes, such as Na+, Cl-, K+, and Ca2+. We measure each

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Medicinal Chemistry lectures by Asist.Prof.Dr.Alaa J.Mahrath

individual ion in terms of an equivalent (Eq), which is the amount of that ion equal to 1 mole of positive or negative electrical charge. For example, 1 mole of Na+ ions and 1 mole of Cl - ions are each 1 equivalent because they each contain 1 mole of charge. For an ion with a charge of 2+ or 2-, there are 2 equivalents

for each mole. Some examples of ions and equivalents are shown in Table 9.5.

In any solution, the charge of the positive ions is always balanced by the charge of the negative ions. The concentrations of electrolytes in intravenous fluids are expressed in milliequivalents per liter (mEq/L); 1 Eq = 1000 mEq. For example, a solution containing 25 mEq/L of Na+ and 4 mEq /L of K +

has a total positive charge of 29 mEq /L. If Cl- is the only anion, its concentration must be 29 mEq/L.

Electrolytes in the Body FluidsElectrolytes in the body play an important role in maintaining the proper function of the cells and organs in the body. Typically, the electrolytes sodium, potassium, chloride, and bicarbonate are measured in a blood test. Sodium ions regulate the water content in the body and are important in carrying electrical impulses through the nervous system. Potassium ions are also involved in the transmission of electrical impulses and play a role in the maintenance of a regular heartbeat. Chloride ions balance the charges of the positive ions and also control the balance of fluids in the body. Bicarbonate is important in maintaining the proper pH of the blood. Sometimes when vomiting, diarrhea, or sweating is excessive, the concentrations of certain electrolytes may decrease. Then fluids such as Pedialyte may be given to return electrolyte levels to normal.

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Medicinal Chemistry lectures by Asist.Prof.Dr.Alaa J.Mahrath

The concentrations of electrolytes present in body fluids and in intravenous fluids given to a patient are often expressed in milliequivalents per liter 1mEq>L2 of solution. For example, one liter of Pedialyte contains the following electrolytes: Na+ 45 mEq, Cl- 35 mEq, and citrate3- 30 mEq. Table 9.6 gives the concentrations of some typical electrolytes in blood plasma. There is a charge balance because the total number of positive charges is equal to the total number of negative charges. The use of a specific intravenous solution depends on the nutritional, electrolyte, and fluid needs of the individual patient. Examples of various types of solutions are given in Table 9.7.

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