solute potential

Examples of solute potential in the following topics:

• Water and Solute Potential

  • The water potential in plant solutions is influenced by solute concentration, pressure, gravity, and factors called matrix effects.
  • Solute potential (Ψs), also called osmotic potential, is negative in a plant cell and zero in distilled water.
  • Solutes reduce water potential (resulting in a negative Ψw) by consuming some of the potential energy available in the water.
  • In other words, the amount of available potential energy is reduced when solutes are added to an aqueous system.
  • This is why solute potential is sometimes called osmotic potential.

• Pressure, Gravity, and Matric Potential

  • Water potential is affected by factors such as pressure, gravity, and matric potentials.
  • A plant can manipulate Ψp via its ability to manipulate Ψs (solute potential) and by the process of osmosis.
  • If a plant cell increases the cytoplasmic solute concentration:
  • Ψm is similar to solute potential because the hydrogen bonds remove energy from the total system.
  • However, in solute potential, the other components are soluble, hydrophilic solute molecules, whereas in Ψm, the other components are insoluble, hydrophilic molecules of the plant cell wall. m cannot be manipulated by the plant and is typically ignored in well-watered roots, stems, and leaves.

• Standard Reduction Potentials

  • Reduction potential (also known as redox potential, oxidation/reduction potential, or Eh) measures the tendency of a chemical species to acquire electrons and thereby be reduced.
  • Reduction potential is measured in volts (V) or millivolts (mV).
  • Each species has its own intrinsic reduction potential.
  • The values below in parentheses are standard reduction potentials for half-reactions measured at 25 °C, 1 atmosphere, and with a pH of 7 in aqueous solution.
  • However, because these can also be referred to as "redox potentials," the terms "reduction potentials" and "oxidation potentials" are preferred by the IUPAC.

• Predicting if a Metal Will Dissolve in Acid

  • A metal is soluble in acid if it displaces H2 from solution, which is determined by the metal's standard reduction potential.
  • Here, zinc is more active than copper because it can replace copper in solution.
  • The blue color of the solution diminishes as copper(II) ion is being replaced.
  • The tendency of a metal to "replace" hydrogen gas from acidic solution will determine its solubility in that solution.
  • For this reason, the potential difference contributed by the left half-cell has the opposite sign to its conventional reduction half-cell potential.

• Intermolecular Forces and Solutions

  • To form a solution, molecules of solute and solvent must be more attracted to each other than themselves.
  • 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 this case, the potential energy is lower when the solute and solvent can form bonds.
  • Recall the two conceptual steps necessary to dissolve a solute and form a solution

• Thermodynamics of Redox Reactions

  • The thermodynamics of redox reactions can be determined using their standard reduction potentials and the Nernst equation.
  • The Nernst equation allows the reduction potential to be calculated at any temperature and concentration of reactants and products; the standard reaction potential must be measured at 298K and with each solution at 1M.
  • This equation allows the equilibrium constant to be calculated just from the standard reduction potential and the number of electrons transferred in the reaction.
  • The relationship between the Gibbs free energy change and the standard reaction potential is:
  • Translate between the equilibrium constant/reaction quotient, the standard reduction potential, and the Gibbs free energy change for a given redox reaction

• Electrolytic Properties

  • Electrolysis reactions involving H+ ions are fairly common in acidic solutions, while reactions involving OH- (hydroxide ions) are common in alkaline water solutions.
  • In order to determine which species in solution will be oxidized and which will be reduced, the standard electrode potential of each species may be obtained from a table of standard reduction potentials, a small sampling of which is shown here:
  • If a problem demands use of oxidation potential, it may be interpreted as the negative of the recorded reduction potential.
  • Positive potential is more favorable in this case.
  • Use a table of standard reduction potentials to determine which species in solution will be reduced or oxidized.

• Equilibrium Constant and Cell Potential

  • If possible, a species will move from areas with higher electrochemical potential to areas with lower electrochemical potential.
  • We say the ions have electric potential energy, and are moving to lower their potential energy.
  • We can also consider an example where the solutions are CuSO4 and ZnSO4.
  • Each solution has a corresponding metal strip in it, and a salt bridge or porous disk connecting the two solutions.
  • This allows SO42- ions to flow freely between the copper and zinc solutions.

• Free Energy and Cell Potential

  • Electricity is generated due to the electric potential difference between two electrodes.
  • In electrochemistry, the standard electrode potential, abbreviated E°, is the measure of the individual potential of a reversible electrode at standard state, which is with solutes at an effective concentration of 1 M, and gases at a pressure of 1 atm.
  • Since the standard electrode potentials are given in their ability to be reduced, the bigger the standard reduction potentials, the easier they are to be reduced; in other words, they are simply better oxidizing agents.
  • For example, F2 has a potential of 2.87 V and Li+ has a potential of -3.05 V.
  • In the example of Zn2+, whose standard reduction potential is -0.76 V, it can be oxidized by any other electrode whose standard reduction potential is greater than -0.76 V and can be reduced by any electrode with standard reduction potential less than -0.76 V.

• Medical Solutions: Colligative Properties

  • These electrolytic solutions share the same colligative properties as chemical solutions.
  • One class of medical solutions is known as saline solutions.
  • These solutions are composed of water and sodium chloride.
  • Saline solutions can vary in their concentrations.
  • Therefore, the introduction of saline that is too hypotonic will cause water to fill the cells too rapidly, potentially causing the cells to burst.