12: Dissolving into Solutions in Visual Studio .NET

Encoder EAN13 in Visual Studio .NET 12: Dissolving into Solutions

own O H bond, but is less polar than water In solution, water molecules can orient their dipoles cleanly and in either of two directions to interact favorably with Na+ or Cl ions Methanol molecules can engage in favorable interactions with these ions too, but not nearly as well as water

Lattice energy is a measure of the strength of the interactions between ions in the lattice of an ionic solid The larger the lattice energy, the stronger the ion-ion interactions Here is a table of ionic solids and their associated lattice energies Predict the rank order of solubility in water of these ionic solids Sodium Salt NaBr NaCl NaF NaI Lattice Energy, kJ mol 1 747 787 923 704

Ethanol, CH3CH2OH, is miscible with water Octanol, CH3(CH2)7OH, isn t miscible in water Is sucrose (as in table sugar) likely to be more soluble in ethanol or octanol Why

Increasing temperature magnifies the effects of entropy on a system Because the entropy of a solute is usually increased when it dissolves, increasing temperature usually increases solubility for solid and liquid solutes, anyway Another way to understand the effect of temperature on solubility is to think about heat as a reactant in the dissolution reaction: Solid solute + Water + Heat Dissolved solute Heat is usually absorbed when a solute dissolves Increasing temperature corresponds to added heat So, by increasing temperature you supply a needed reactant in the dissolution reaction (In those rare cases where dissolution releases heat, increasing temperature can decrease solubility)

Gaseous solutes behave differently than do solid or liquid solutes with respect to temperature Increasing the temperature tends to decrease the solubility of gas in liquid To understand this pattern, check out the concept of vapor pressure (If creaking sounds emanate from your skull as you try to remember what vapor pressure is about, take a peek at 11) Increasing temperature increases vapor pressure because added heat increases the kinetic energy of the particles in solution With added energy, these particles stand a greater chance of breaking free from the intermolecular forces that hold them in solution A classic, real-life example of temperature s effect on gas solubility is carbonated soda Which goes flat (loses its dissolved carbon dioxide gas) more quickly: warm soda or cold soda The comparison of gas solubility in liquids with the concept of vapor pressure highlights another important pattern: Increasing pressure increases the solubility of a gas in liquid Just as high pressures make it more difficult for surface-dwelling liquid molecules to escape into vapor phase, high pressures inhibit the escape of gases dissolved in solvent The relationship between pressure and gas solubility is summarized by Henry s Law: Solubility = Constant Pressure The constant is Henry s Constant, and its value depends on the gas, solvent, and temperature A particularly useful form of Henry s Law relates the change in solubility (S) that accompanies a change in pressure (P) between two different states: S1 / P1 = S2 / P2 According to this relationship, tripling the pressure triples the gas solubility, for example

Henry s Constant for dinitrogen gas in water at 293K is 069 10 3 mol L 1 atm 1 The partial pressure of dinitrogen in air at sea level is 078 atm What is the solubility of N2 in a glass of water at 20 C sitting on a coffee table within a beach house 054 10 3 mol L 1 This problem requires the direct application of Henry s Law

The glass of water is at 20 C, which is equivalent to 293K (just add 273 to any Celsius temperature to get the Kelvin equivalent) Because the glass sits within a beach house, we can assume the glass is at sea level So, we can use the provided values for Henry s Constant and the partial pressure of N2 Solubility = (069 10 3 mol L 1 atm 1) (078 atm) = 054 10 3 mol L 1