Solutions Chapter 6

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SolutionsChapter 6

• Dr. Michael P. Gillespie

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Properties of Solutions

• A solution is a homogenous (uniform) mixture of
  two or more substances.
• A solution is composed of one or more solutes,
  dissolved in a solvent.
• The solute is a compound of a solution that is
  present in lesser quantity than the solvent.
• The solvent is the solution component that is
  present in the largest quantity.
• An aqueous solution is one in which water is the
  solvent.

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Solution
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Example of a Solution

• When sugar (the solute) is added to water (the
  solvent), the sugar dissolves in the water to
  produce a solution.
• This mixture is an aqueous solution because water
  is the solvent.

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Types of Solutions

• The dissolution of a solid into a liquid is the
  most common example of solution formation
  however, it is possible to form solutions in
  gases and solids as well as liquids.
• Air is a gaseous mixture, but it is also a
  solution. Oxygen and some other trace gasses
  are dissolved in the gaseous solvent nitrogen.
• Many important biochemical reactions occur in
  liquid solutions, so our emphasis will be placed
  there.

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Properties of Liquid Solutions

• Liquid solutions are clear and transparent with
  no visible particles of solute.
• They can be either colored or colorless.

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Electrolyte and Nonelectrolyte Solutions

• An electrolyte is a material that dissolves in
  water to produce a solution that conducts an
  electrical current.
• Solutions of electrolytes are formed from solutes
  that are soluble ionic compounds.
• Good conductors of electricty
• Sodium Chloride dissolving in water
• Solutions of nonelectrolytes are formed from
  nondissociating molecular solutes.
• Nonconducting
• Sugar dissolving in water

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Electrolyte
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True Solutions

• A true solution is a homogenous mixture with
  uniform properties throughout.
• The solute cannot be isolated from the solution
  by filtration.
• The particle size of the solute and solvent are
  about the same and both pass directly through the
  filter paper.
• Solute particles will not settle out over time.

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True Solutions

• All of the molecules of solute and solvent are
  intimately mixed.
• The particles are in continuous motion and
  therefore maintain a homogenous, random
  distribution of solute and solvent particles.
• Volumes of solute and solvent are not additive.
• 1 L of alcohol mixed with 1 L of water does not
  result in exactly 2L of solution.
• It depends upon how the molecules fit together.

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Solution, Pure Substance, or Colloidal Suspension?

• A beaker containing a clear liquid may be a
  pure substance, a true solution, or a colloid.

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Solution Vs. Pure Substance

• Only chemical analysis can distinguish between a
  pure substance and a true solution.
• A pure substance has only one component.
• A true solution has more than one substance, with
  the tiny particles homogenously intermingled.

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Colloidal Suspension

• A colloidal suspension also consists of solute
  particles distributed throughout a solvent
  however, the distribution is not completely
  homogenous, due to the size of the colloidal
  particles.
• Particles smaller than 1 nm are solution
  particles.
• Particles between 1 nm and 200 nm are colloids.
• Particles larger than 200 nm are precipitates
  (solid in contact with solvent).

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Solution Vs. Colloidal Suspension

• To the naked eye, a colloidal suspension and a
  true solution appear identical. Neither the
  solute nor the colloid can be seen by the naked
  eye.
• Colloid particles are large enough to scatter
  light, whereas solute particles are not.
• When a beam of light passes through a colloidal
  solution, the large particles scatter light, and
  the liquid appears hazy. Similar to sunlight
  passing through fog.
• Tyndall effect the light-scattering ability of
  solutions.

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Suspension

• A suspension is a heterogeneous mixture that
  contains particles much larger than a colloidal
  suspension.
• These particles can settle out over time.

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Colloidal Suspension
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Polarity and Solubility

• Like dissolves like.
• Polar solutes are soluble in polar solvents.
• Nonpolar solutes are soluble in nonpolar solvents.

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Degree of Solubility

• The degree of solubility is a measure of how much
  solute can dissolve in a given quantity of
  solvent.
• Factors influencing degree of solubility.
• The magnitude of difference between polarity of
  solute and solvent. (Inverse relationship)
• Temperature. (Usually increases solubility)
• Pressure. (Greater influence on gases)

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Saturation

• A saturated solution contains all of the solute
  that can be dissolved at a particular
  temperature.
• Decreasing the temperature typically decreases
  the amount of solute the solution can hold.
• The excess solute falls to the bottom of the
  container as precipitate (a solid in contact with
  a solution).
• Sometimes the excess solute stays in solution for
  a period of time. The solution is then said to
  be supersaturated (this is an unstable condition).

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Precipitation
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Solubility and Equilibrium

• When an excess of solute is added to a solvent,
  it begins to dissolve and continues to do so
  until it reaches a dynamic equilibrium between
  dissolved and undissolved solute.
• The rate of dissolution and precipitation
  eventually become equal.
• There is a continual exchange of particles
  between solid and liquid phases.

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Henrys Law

• Henrys Law states that the number of moles of a
  gas dissolved in a liquid at a given temperature
  is directly proportional to the partial pressure
  of the gas.
• The gas solubility is directly proportional to
  the pressure of that gas in the atmosphere that
  is in contact with the liquid.
• Gases are most soluble at low temperatures.
• Henrys law has a direct application to
  respiration in the lungs.

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Henrys Law
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Henrys Law
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Concentration Based on Mass

• A solution concentration is the amount of solute
  dissolved in a given amount of solution.
• The concentration of a solution affects its
  physical properties such as melting and boiling
  points.
• The concentration also affects its chemical
  properties influencing its reactivity.

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Weight / Volume Percent

• Concentration amount of solute / amount of
  solution
• Concentration grams of solute / milliliters of
  solution
• concentration grams of solute / milliliters
  of solution 100

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Molarity

• Molarity (M) is the number of moles of solute per
  liter of solution.
• A Mole is a collection of atoms.
• 1 mol of atoms 6.022 X 1023 atoms of an
  element. This number is Avogadros number.
• The mass of 1 mol of atoms is defined as the
  molar mass.
• One mole of atoms of any element contains the
  same number of atoms (6.022 X 1023 atoms).

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Dilution

• Laboratory reagents are often purchased as
  concentrated solutions for safety, economic, and
  space limitation reasons.
• We often must dilute the solution to prepare a
  less concentrated form for our experiment.

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Dilution
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Colligative Properties

• Colligative properties are properties of
  solutions that depend on the concentration of the
  solute particles, rather than the identity of the
  solute.
• 1. vapor pressure lowering
• 2. freezing point depression
• 3. boiling point elevation
• 4. osmotic pressure

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Vapor Pressure Lowering (Raoults Law)

• Raoults law states that, when a nonvolatile
  solute is added to a solvent, the vapor pressure
  of the solvent decreases in proportion to the
  concentration of the solute.
• This has a direct effect on the freezing and
  boiling points of a solution.
• The freezing point decreases.
• The boiling point increases.

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Freezing Point DepressionBoiling Point Elevation

• The solute molecules interfere with the rate at
  which liquid water molecules associate to form
  the solid state.
• Salt is spread on ice in the winter because it
  lowers the freezing point of water.
• 1 mol of glucose ? 1 mol of particles in solution
• 1 mol of sodium chloride ? 2 mol of particles in
  solution

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Osmotic Pressure

• Some membranes are semipermeable. They all small
  solvent molecules such as water to cross
  however, larger solute particles are too large to
  get through the small pores of the membrane.
• Osmosis is the diffusion of a solvent from a
  dilute solution to a more concentrated solution
  through a semipermeable membrane.
• Pressure must be applied to the more concentrated
  solution to stop the flow. Osmotic pressure is
  the amount of pressure required to stop the flow.

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Osmosis
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Hypertonic, Hypotonic, Isotonic

• Hypertonic Water leaves a cell via osmosis.
  The cell undergoes crenation (shrinkage).
• Hypotonic Water enters a cell via osmosis. The
  cell undergoes hemolysis (ruptures).
• Isotonic Two solutions are isotonic if they
  have identical osmotic pressures.

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Crenation Hemolysis
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Water as a Solvent

• Water is often referred to as the universal
  solvent.
• It is the principle biological solvent.
• Water is a polar molecule. Much of the matter on
  earth is polar. Like dissolves like.

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Properties of Water

• Water is the only common molecule that exists in
  all three physical states of matter (solid,
  liquid, and gas) under natural conditions on
  earth.
• Water is essential for all life.
• Water is the most abundant molecule in living
  systems (70-95).
• Water covers 70 of the earths surface.

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Properties of Water

• Water has an unusually high specific heat and can
  therefore resist changes in temperature. It
  stabilizes temperatures on both earth and in the
  body.
• Water has a very high heat of vaporization.
• As water evaporates, the surface of the liquid
  cools. Perspiration helps to prevent overheating
  on a hot day or during strenuous exercise.
• The solid state of water is less dense than the
  liquid state (about 10 less dense).

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Solutes in Blood

• An electrolyte is a material that dissolves in
  water to produce a solution that conducts an
  electrical current.
• The concentration of cations, anions, and other
  substances in body fluids is critical to health.
• The kidneys carefully regulate these levels.
• Na and K are the two most important cations in
  body fluids.
• Sodium is more abundant in intercellular fluids
  and potassium is more abundant in intracellular
  fluids. (Active transport)
• If potassium levels become too high from cell
  death (leakage) or too low from excessive
  sweating, heart failure can ensue.

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Solutes in Blood

• The major anions in blood are Cl- and HCO3-.
• Chloride anion helps with acid-base balance,
  osmotic pressure, and oxygen transport by
  hemoglobin.
• Bicarbonate anion helps transport CO2 in the
  blood.
• Plasma proteins blood clotting factors,
  immunoglobulins (antibodies), and albumins (carry
  non-polar substances).
• Nutrients and waste products.

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Hemodialysis

• Dialysis the kidneys remove waste products such
  as urea and uric acid as well as excess salts
  from the blood. This process is known as
  dialysis.
• Hemodialysis is the use of an artificial kidney
  to remove waste products from the blood.

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Hemodialysis