4.1.4 Factors Determining Solubility Flashcards
Factors Determining Solubility
- Polar solutes dissolve in polar solvents.
* Nonpolar solutes dissolve in nonpolar solvents
elements
- Elements on the left of the periodic table are electron rich (electropositive). Elements on the right of the periodic table are electron needing (electronegative). Elements from opposite sides of the periodic table tend to form ionic bonds.
- Hydrogen and oxygen have different affinities for electrons. The bond between hydrogen and oxygen is still a covalent bond, but the large difference in the electronegativity of hydrogen and oxygen results in a large dipole moment—the hydrogen atoms are partially positive ( ), and the oxygen atom is partially negative ( ). A covalent bond in which the electrons are distributed unevenly between the two bonding atoms is called a polar covalent bond.
- Ions can dissolve in polar solvents (such as water). This is because the dipoles on the solvent molecules shield the charges of the solute (for example, the positive charge on sodium ion or the negative charge on chloride ion). This shielding prevents the ions from “seeing” one another to form an ionic bond.
solubility
- Solubility of nonpolar solutes is governed by the changes in disorder of the system, rather than by attractions between charges. This disorder is called entropy. The entropy of a system tends to want to increase.
- When a polar solute in a spontaneous reation is added to a nonpolar solvent (hexane), the solvent is forced to become more ordered to accommodate the polar solute. Therefore, polar solutes tend not to dissolve in nonpolar solvents. Similarly, when a nonpolar solute (oil) is added to a polar solvent (water), the entropy decreases. Therefore, nonpolar solutes tend not to dissolve in polar solvents. However, when a nonpolar solute (oil) is added to a nonpolar solvent (hexane), the entropy increases. Therefore, nonpolar solutes dissolve in nonpolar solvents.
When the ionic compound KOH is dissolved in water, how will the water molecules be oriented with respect to the potassium ions?
- Potassium ions have a positive charge. Therefore, the partially negative portion of water molecules (the oxygen atoms) will be attracted to these ions. In this diagram, each of the water molecules is oriented so that its oxygen atom points toward the potassium ion.
Which of these methods would best allow you to distinguish between a sample of pure water and a sample of pure ethanol?
Stir several grams of Potassium Chloride into each sample.
Sugar (C12H22O11 ) readily dissolves in water. Which of the following is the most likely explanation of sugar’s solubility?
It is polar and can interact with the polar water molecules.
Water molecules are bent as shown in the diagram below. Suppose, however, that water molecules were linear. How would this change in structure most likely affect the properties of water?
The solubility of salt in water would decrease.
What will occur when hexane is added to a solution of water and salt?
The hexane will form a separate layer, and the salt will remain dissolved in the water.
The fluid inside and surrounding the cells of your body is an aqueous solution. The membrane around cells that forms the boundary between these two solutions consists mainly of compounds called phospholipids. These compounds have two parts: One part is polar and one part is nonpolar. Which of these diagrams represents the structure of a cell membrane?
In this structure, the polar ends of the phospholipids are exposed only to the aqueous solutions inside and outside the cell. Because polar compounds will dissolve in aqueous solutions, this arrangement will tend to increase the stability of the membrane. In addition, the nonpolar ends of the phospholipids are exposed only to the nonpolar ends of other phospholipids. Because nonpolar compounds tend to dissolve in other nonpolar compounds, this arrangement will also increase the stability of the membrane. Of the four choices given, answer C will be the most stable.
Which of the following processes is an example of increasing entropy?
Sugar dissolving in water.
The compound CH3(CH2 )4CH2OH is only slightly soluble in water. (This compound is identical to hexane except that one of the hydrogen atoms has been replaced with the −OH group of an alcohol.) A second compound has the formula HOCH2(CH2 )4CH2OH. (It is identical to the first compound except that it has two −OH groups instead of one.) How is the solubility of the second compound likely to compare to that of the first compound in water?
The second compound is likely to be more soluble in water.
Which of these diagrams best represents a solution of cyclohexane (the solute) dissolved in hexane (the solvent)? (Cyclohexane is a nonpolar compound composed of hydrogen and carbon.)
Cyclohexane and hexane are both nonpolar compounds. Therefore, the solution of these compounds will depend on entropy rather than on dipole interactions between the solvent and the solute. Entropy acts to increase the randomness of a system. Therefore, the molecules of cyclohexane and hexane will be dispersed randomly throughout the solution. Of the four diagrams, choice A shows the most disordered arrangement of these two molecules.
Solid iodine (I2 ) is nearly insoluble in water, somewhat soluble in ethanol, and very soluble in hexane. Based on this information, what can you conclude about I2?
It contains a nonpolar bond.
