SOLUTIONS

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SOLUTIONS

• Chapter 13

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What is a solution?

• In chemistry, a solution is a homogenous mixture
  composed of two or more substances. In such a
  mixture, a solute is dissolved in another
  substance, known as a solvent. A common example
  is a solid, such as salt or sugar, dissolved in
  water,a liquid.
• A mixture is a substance made by combining two or
  more different materials in such a way that no
  chemical reaction occurs. The objects do not bond
  together in a mixture. A mixture can usually be
  separated back into its original components. Some
  examples of Mixtures are oil, ocean water and
  soil.

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• A suspension is a heterogenous fluid containing
  solid particles that are sufficiently large for
  sedimentation.
• A colloid is a homogeneous solution with
  intermediate particle size between a solution and
  a suspension.

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What is concentration?

• Solvent The substance in which the solute
  dissolves to make the solution.
• Solute The substance dissolved in a solution.
• Aqueous Describes a solution in which the
  solvent is water.
• Concentration The quantity of solute in a
  specific quantity of solvent or solution.
• Molarity A concentration unit, expressed in
  moles of solute per liter of solution.

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• Molarity(M) moles of solute/liters of
  solutionmol/L

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Class Practice

• What is the molarity of a potassium chloride
  solution that has a volume of 400 ml and contains
  85 g of KCl?
• Sodium thiosulfate, Na2S2O3, is used as a fixer
  when developing photographic film. What is the
  mass in grams of Na2S2O3 needed to make 100ml of
  a 0.250M solution?

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Home work

• Page 475 Practice problems do all odd .

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Separating mixtures

• There are many ways to separate mixtures into
  their components.

filtering
Magnetic separation
distillation
chromatography
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Different ways of separating mixture

• 1 A magnet can be used to separate IRON from
  SAND.
• How it works The magnet sticks to the iron but
  not to the sand.
• 3. Filtering (filtration) can be used to separate
  a solid (or suspension) from a liquid.
• How it works The liquid (and anything dissolved
  in the liquid) passes through holes in the filter
  paper but the solid particles are too big and get
  stuck.
• Example Filtration would be used to separate the
  dirt from some salty water.
• 4. Evaporation can be used to separate a
  dissolved SOLUTE from a SOLUTION
• Example Evaporation would be used to obtain some
  pure salt from salty water.
• How it works When salty water is warmed the
  water evaporates leaving behind crystals of salt.

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• Distillation is a method of separating chemical
  substances based on differences in their
  volatilities in a boiling liquid mixture.
  Example Used to separate crude oil into more
  fractions for specific uses such as transport,
  power generation and heating.
• Chromatography is a physical method of separation
  in which the components to be separated are
  distributed between two phases, one which is the
  stationary (stationary phase) while the other
  (the mobile phase) moves in a definite
  direction..

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Gas Solubility

• Gases can dissolve in liquids Gases may dissolve
  in liquids, for example, carbon dioxide or oxygen
  in water.
• Gas solubility depends on pressure A soda bottle
  can be considered to be saturated since there is
  some soda above the liquid level and some is in
  the liquid itself.In an unopened soda bottle
  there is much higher partial pressure of CO2 in
  the neck of the bottle, above the liquid than
  there is in the air outside the bottle. Due to
  this difference in the pressure the CO2 dissolves
  in the liquid.

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• Gas solubility decreases with increasing
  temperature After the soda bottle is opened the
  soda is allowed to warm, the soda forms fewer
  bubbles and tastes flat.

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Liquids and miscibilities

• Miscible Indicates liquids that will dissolve in
  each other.
• Immiscible Indicates liquids that will not
  dissolve appreciably in each other example oil
  and water.

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Polarity of the solute and solvent

• Polar solvents dissolve polar compounds, and non
  polar solvents dissolve non polar compounds
  example when a sugar cube having polar sucrose
  molecules is dissolved in water a polar solvent.

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• Hydrogen bonding High solubility is expected
  when hydrogen bonds form between solute and
  solvent molecules.
• Two compounds that are both polar or both non
  polar are likely to be miscible.
• Two compounds that can form hydrogen bonds with
  each other are likely to be miscible.

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Solubility principles at work

• Dry cleaners use solubility principles to remove
  stains. Commonly used dry cleaning solvent is
  tetrachloro ethylene C 2Cl4.
• Vitamin C dissolves in water. Some sources of
  vitamin C are,

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• Vitamin A dissolves in oils and fats. Vitamin A
  affects vision because the human body uses it to
  make a pigment called visual purple, one of the
  vital light sensitive molecule in the retina.

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Conductivity in Solutions

• Conductivity is a measure of waters ability to
  conduct electrical current. Measurements of
  conductivity provide a general indication of
  water quality.

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• Electrical conductivity is a measure of a
  material's ability to conduct an electric
  current. When an electrical potential difference
  is placed across a conductor, its movable charges
  flow, giving rise to an electric current. The
  conductivity s is defined as the ratio of the
  current density to the electric field strength

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Electrolytes

• What are electrolytes?
• Electrolytes are substances that become ions in
  solution and acquire the capacity to conduct
  electricity.
• Non electrolyte is a substance that does not
  dissociate into ions and so in solution it is a
  nonconductor of electricity.

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Non electrolyte in solution
Weak electrolyte
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Strong electrolyte
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• Tap water conducts electricity
• You should avoid water when you are using
  electricity. Unlike distilled water that does not
  conduct enough electricity to light a bulb in the
  conductivity apparatus tap water contains various
  ions from dissolved minerals. Water sources like
  water from a well has more concentration of salts
  than the surface water such as lakes and rivers.

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• While swimming in the pool, get out of the pool
  if a thunderstorm strikes. Chlorinated water
  conducts electricity.

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• Dissociation A process in which a compound
  separates into fragments, such as simpler
  molecules,atoms,radicals or ions.
• Hydration The process by which water molecules
  surround each ion as it moves into solution.

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Factors affecting solubility

• TemperatureThe solubility of a given solute in a
  given solvent often depends on temperature. For
  around 95 of solid solutes, the solubility
  increases with temperature, but gaseous solutes
  exhibit more complex behavior. As the temperature
  is raised gases usually become less soluble in
  water, but more soluble in organic solvents.

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• PressureHenrys Law states that the solubility
  of a gas is directly proportional to the pressure
  of that gas, which may be written as pkc
• where k is a constant.
• Polarity "Like dissolves like" This indicates
  that a solute will dissolve best in a solvent
  that has a similar polarity to itself. For
  example, a very polar (hydrophilic) solute such
  as urea is highly soluble in highly polar water,
  less soluble in fairly polar methanol, and
  practically insoluble in non-polar solvents such
  as benzene.

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Colligative properties

• Colligative properties of solutions are
  properties that depend upon the concentration of
  solute molecules or ions, but not upon the
  identity of the solute. Colligative properties
  include
• 1. freezing point depression the difference
  between the freezing point of a pure solvent and
  that of a solution.
• 2. boiling point elevationthe difference between
  the boiling point of a solution and that of the
  pure solvent.
• 3.vapor pressure lowering, and osmotic pressure.

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• The concentration of the solute affects freezing
  and boiling point changes The more particles
  there are the greater the freezing point
  depression and the boiling point elevation. Based
  on the number of moles of solute particles
  produced, 1 mole of sodium chloride is expected
  to be twice as effective dissolved in water as 1
  mol of sucrose,
• C12H22O11(s)H2O-? C12H22O11 (aq)
• NaCl(s)-H2O?Na(aq)Cl-(aq)

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Emulsions

• An emulsion is a mixture of two immiscible
  substances. One substance is dispersed in the
  other Examples of emulsions include butter and
  margarine, espresso, mayonnaise, the
  photo-sensitive side of photographic film, and
  cutting fluid for metal working. In butter and
  margarine, a continuous liquid phase surrounds
  droplets of water (water-in-oil emulsion).
  Emulsification is the process by which emulsions
  are prepared.

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Surfactant

• What is soap? A sodium or potassium salt of a
  long chain fatty acid. If the skin has
  accumulated oil dirt and bacteria then to remove
  this one must first emulsify the oil by scrubbing
  then stabilize it with an emulsifier such as
  soap.
• Only then can the soap and oily dirt emulsion be
  rinsed away from the skin.

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• The soap ion dissolves the oil, forming a tiny
  sphere called a micelle, while the other end on
  the outside of the micelle dissolves in the
  surrounding water. The oil droplet stays
  suspended in the water and can be easily washed
  away. The characteristic property of a surfactant
  is its ability to form a layer between two
  dissimilar phases.

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• Soap forms micelle which is the bubble.A thin
  film of water is coated on both surfaces by soap
  molecules.

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• Hard water destroys soaps surfactant abilities.
• Detergents outperform soaps in hard water.

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Homework

• Page 504
• Term review all
• Test prep all
• Q.9 b
• Q 10 all
• Q.24 and 32 all