solvent

Examples of solvent in the following topics:

• Solvent Effects

  • Polar, protic solvents such as water and alcohols solvate anions by hydrogen bonding interactions, as shown in the diagram below.
  • Polar, aprotic solvents such as DMSO (dimethyl sulfoxide), DMF (dimethylformamide) and acetonitrile do not solvate anions nearly as well as methanol, but provide good solvation of the accompanying cations.
  • Consequently, most of the nucleophiles discussed here react more rapidly in solutions prepared from these solvents.
  • These solvent effects are more pronounced for small basic anions than for large weakly basic anions.

• The Leveling Effect

  • The leveling effect, or solvent leveling, is an effect that places an upper-limit on the strength of an acid (or base) in a given solvent when the solvent is Lewis acidic or Lewis basic.
  • The strength of a strong acid is limited ("leveled") by the basicity of the solvent.
  • Similarly, the strength of a strong base is leveled by the acidity of the solvent.
  • Strong bases are leveling solvents for acids, weak bases are differentiating solvents for acids.
  • Because of the leveling effect of common solvents, studies on super acids are conducted in solvents that are very weakly basic such as sulfur dioxide (liquefied) and SO2ClF (these solvents would be considered differentiating solvents).

• Solvent Effects

  • This characteristic is a function of the polarity of the solvent.
  • Solvents that have relatively acidic hydrogen atoms (e.g.
  • A list of common protic and aprotic solvents is provided here.
  • The dielectric constants provide a measure of solvent polarity.
  • This refers to the ability of solvent molecules to stabilize ions by encasing them in a sheath of weakly bonded solvent molecules, thus somewhat dispersing the electrical charge.

• Intermolecular Forces and Solutions

  • The strength of the intermolecular forces between solutes and solvents determines the solubility of a given solute in a given solvent.
  • In order to form a solution, the solute must be surrounded, or solvated, by the solvent.
  • Solutes successfully dissolve into solvents when solute-solvent bonds are stronger than either solute-solute bonds or solvent-solvent bonds.
  • In general, solutes whose polarity matches that of the solvent will generally be soluble.
  • In this case, the potential energy is lower when the solute and solvent can form bonds.

• Vapor Pressure of Nonelectrolyte Solutions

  • When a solute is added to a solvent, the vapor pressure decreases.
  • The vapor pressure of a solvent is lowered by the addition of a non-volatile solute to form a solution.
  • If the liquid solvent becomes "diluted" with solute, the entropy of the liquid state increases.
  • Overall, less solvent will transition to the gaseous phase, resulting in a decrease in vapor pressure.
  • In this equation, $p^{\star}_{\rm A}$ is the vapor pressure of the pure solvent and $x_{\rm A}$ is the mole fraction of the solvent.

• Heat of Solution

  • Heat of solution refers to the change in enthalpy when a solute is dissolved into a solvent.
  • The breaking of intermolecular attractive forces within the solvent, such as hydrogen bonds (endothermic)
  • This depends entirely on if more energy was used to break the solute-solute and solvent-solvent bonds, or if more energy was released when solute-solvent bonds were formed.
  • If more energy is used in breaking bonds than is released upon solute-solvent bond formation, then the overall process is endothermic, and ∆Hsol is positive.
  • Solute-solvent attractive bond formation (the exothermic step in the process of solvation) is indicated by dashed lines.

• Vapor Pressure of Electrolyte Solutions

  • The vapor pressure of an electrolytic solution is dependent on the ratio of solute to solvent molecules in a solution.
  • To better visualize the effect of solute on the vapor pressure of a solution, consider a pure solvent.
  • This pure solvent has a certain vapor pressure associated with it.
  • Now consider a solution composed of both solvent and solute.
  • Compare the relative vapor pressures of a pure solvent and an electrolyte solution composed of the same solvent

• Molality

  • Molality is a property of a solution that indicates the moles of solute per kilogram of solvent.
  • The SI unit for molality is mol/kg, or moles solute per kg of solvent.
  • It is easy to calculate molality if we know the mass of solute and solvent in a solution.
  • Remember that molality is moles of solute/kg per solvent.
  • KCl is our solute, while water is our solvent.

• Osmotic Pressure

  • A solution is defined as a homogeneous mixture of both a solute and solvent.
  • Solutions generally have different properties than the solvent and solute molecules that compose them.
  • Osmosis is defined as the net flow or movement of solvent molecules through a semipermeable membrane through which solute molecules cannot pass.
  • If a solution consisting of both solute and solvent molecules is placed on one side of a membrane and pure solvent is placed on the other side, there is a net flow of solvent into the solution side of the membrane.
  • The height difference between the two sides can be be converted into pressure to find the osmotic pressure exerted on the solution by the pure solvent.

• Solubility

  • Solubility is the relative ability of a solute (solid, liquid, or gas) to dissolve into a solvent and form a solution.
  • The solubility of a substance fundamentally depends on the solvent used, as well as temperature and pressure.
  • The solubility of a substance in a particular solvent is measured by the concentration of the saturated solution.
  • The solubility of a given solute in a given solvent typically depends on temperature.
  • This statement indicates that a solute will dissolve best in a solvent that has a similar chemical structure; the ability for a solvent to dissolve various compounds depends primarily on its polarity.