OBJ 13.3 NOTES 13-2

13.3 FACTORS AFFECTING SOLUBILITY A.) Solute-Solvent Interactions: 1.) determining solubility is the natural tendency of substances to mix (the tendency of systems to move toward a more dispersed, or random state). 2.) Pairs of liquids that mix in all proportions are miscible. Those that don’t dissolve are considered immiscible

B.) Chemists use the axiom “like dissolves like." Polar substances tend to dissolve in polar solvents. Nonpolar substances tend to dissolve in nonpolar solvents.

C.) The more similar the intermolecular attractions, the more likely one substance is to be soluble in another.

D.) Glucose (which has hydrogen bonding) is very soluble in water, while cyclohexane (which only has dispersion forces) is not.

E.) Vitamin A is soluble in nonpolar compounds (like fats). F.) Vitamin C is soluble in water. G.) Network solids are not soluble in either polar or nonpolar solvents because of the strong bonding forces within the solid.

Sample Exercise 13.2 Predicting Solubility Patterns Predict whether each of the following substances is more likely to dissolve in the nonpolar solvent carbon tetrachloride (CCl 4 ) or in water: C 7 H 16, Na 2 SO 4, HCl, and I 2.

H.) In general, the solubility of gases in water increases with increasing mass. I.) Larger molecules have stronger dispersion forces.

Sample Exercise 13.2 Predicting Solubility Patterns Arrange the following substances in order of increasing solubility in water: Practice Exercise

J.) The solubility of liquids and solids does not change appreciably with pressure. K.) The solubility of a gas in a liquid is directly proportional to its pressure.

L.) HENRY’S LAW S g = kP g where S g is the solubility of the gas, k is the Henry’s Law constant for that gas in that solvent, and P g is the partial pressure of the gas above the liquid.

Sample Exercise 13.3 A Henry’s Law Calculation Calculate the concentration of CO 2 in a soft drink that is bottled with a partial pressure of CO 2 of 4.0 atm over the liquid at 25 °C. The Henry’s law constant for CO 2 in water at this temperature is 3.1 × 10 –2 mol/L-atm. Calculate the concentration of CO 2 in a soft drink after the bottle is opened and equilibrates at 25 °C under a CO 2 partial pressure of 3.0 × 10 –4 atm. Practice Exercise

Why do bubbles form on the inside wall of the cooking pot when water is heated on the stove, even though the temperature is well below the boiling point of water?

M.) TEMPERATURE Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

The opposite is true of gases. Carbonated soft drinks are more “bubbly” if stored in the refrigerator. Warm lakes have less O 2 dissolved in them than cool lakes.