Solutions and Solubility

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Solutions and Solubility
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Solubility

• What does it mean to dissolve?

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Compounds

• Compounds are two or more elements chemically
  joined (held together by chemical bonds)
• There is a fixed ratio of components
• Properties of compound are different from those
  of the components
• Compounds can be separated only by chemical means

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Mixtures

• Mixtures are two or more substances (elements or
  compounds or both) that do not combine chemically
  during the mixing.
• There is a variable proportion of components
• Properties of each component remain the same as
  before mixing
• Parts can be separated by physical means

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More Mixture types

• Alloy mixture of 2 or more metals melted
  together having new and different properties,
  examples bronze, brass, pewter
• Steel is an alloy of iron and carbon.
• Amalgam mixture containing mercury

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• Solvent the substance that is doing the
  dissolving. It is present in the greatest amount.
  
• Solute the substance that is being dissolved
• Solution the solute and the solvent together.
  It is a homogeneous mixture of two or more
  substances.
• Which of these is
• the solvent?

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Solubility

• When the solute particles are evenly distributed
  throughout the solvent, we say that the solute
  has dissolved.

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Solubility

• Chalk and talc do not have solubility values.
• These substances are insoluble in water because
  they do not dissolve in water.

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Solubility

• A solution is saturated if it contains as much
  solute as the solvent can dissolve.
• Any solute added in excess of the substances
  solubility will not dissolve.

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• A supersaturated solution means there is more
  dissolved solute than the maximum solubility.

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• Concentration - a measure of the exact amount of
  solute dissolved in a given amount of solvent.
• Concentration units - similar to density units
• g of solute
• 100 mL of solvent
• or simply g/100mL

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Concentrations may be expressed as

• unsaturated able to hold more solute
• saturated holding exactly the max solute
  possible

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• To calculate concentration EXACTLY use this
  formula
• C mass of solute
• volume of solvent x 100

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Solubility

• Solubility is a measure of how much substance
  (solute) will dissolve at a certain temperature,
  in a certain amount of water or other liquid
  (solvent)

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For Example

• 12g of sugar will dissolve in 100mL of water at
  room temperature. If you heat the water up to
  80C, then 30g of sugar will dissolve. If you
  increase the volume of water to 200mL, then twice
  as much sugar will dissolve as before.
• When expressing the solubility of something you
  must give the amount of water used as well as the
  temperature.

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Solubility is a Characteristic Property

• Solubility changes with temperature so the best
  way to show the solubility of a substance is on a
  graph

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Solubility Rules

• Solid solutes
• Dissolve faster AND more in hotter solvents
• Dissolve faster if stirred or crushed up
•  

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Solubility Rules

• Like Dissolves Like
• Polar molecules dissolve polar molecules (a
  polar molecule has a negative pole on one side
  and a positive one on the other). The charged
  particles attract one another and molecular
  motion spreads the solute evenly through the
  solvent

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Solubility Rules

• Non polar molecules dissolve non-polar molecules
  without charges being involved. A different kind
  of attractive force works on non-polar molecules.

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Solubility Rules

• Gaseous solutes
• Dissolve faster AND more in colder solvents
• Come out of solution when stirred or shaken
• Like Dissolves Like

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Solubility of Gases in Liquids

• When you drink carbonated soda, the fizz comes
  from dissolved carbon dioxide gas (CO2).
• The solubility of gases in liquids increases with
  pressure.

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Liquid Solutes

• Oil and vinegar salad dressing separates because
  oil is not soluble in water.
• Liquids that are not soluble in water may be
  soluble in other solvents.

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Water as a solvent

• Water is often called the universal solvent.
• Water is a good solvent because of the way the
  H2O molecule is shaped.

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Water as a solvent

• A water molecule has a negative end (pole) and a
  positive end.
• A molecule (like water) with a charge separation
  is called a polar molecule.

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Water as a solvent

• Water dissolves sodium chloride (salt) to form a
  solution of sodium () and chlorine (-) ions.

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Water as a solvent

• In general, like dissolves like
• water dissolves polar substances
• non-polar solvents dissolve non-polar substances

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Solutions

• solution - a liquid homogeneous mixture
  containing a dissolved substance
• solvent - substance that dissolves the solute.
  The component in largest concentration.
• solute - substance being dissolved. The component
  in smallest concentration
• aqueous - solvent is water
• tincture - solvent is alcohol

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More on Solutions

• Dilute solutions small amount of solute compared
  to amount of solvent
• Concentrated solution contains more solute than
  a dilute solution
• Saturated solution when solvent cannot hold any
  more solute at a given temperature