Water and its Solutions

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Water and its Solutions
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Important Characteristics of WATER
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1. ICE FLOATS

• Ice is less dense as a solid than as a liquid.
• Below 4 degrees, the volume begins to expand and
  the density decreases
• This property allows aquatic life (fish) to
  survive the winter
• This property also causes pipes to break during
  freezing, and sidewalks to crack

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2. Bent Shape

• Water is not linear because of the two lone pairs
  of electrons on the oxygen.

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3. Polar bonds

• H and O share electrons but not equally.
• The electrons stay closer to the oxygen giving it
  a partial negative charge.
• The hydrogen has a partial positive charge

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4. Hydrogen bonds

• A hydrogen on one water is attracted to an oxygen
  on another water
• This is a type of intermolecular bonding.

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5. High Surface Tension

• Water is resistant to having its surface broken
• This is the reason water forms drops
• Surface tension is the force needed to overcome
  the intermolecular attractions and spread the
  liquid out
• This property allows small animals to walk on
  water

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6. Capillary Action

• Capillarity is the rising of liquid in a narrow
  tube
• This results from the competition between the
  forces within the liquid and from the liquid to
  the tube
• This is the reason water is absorbed by a paper
  towel

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7. High Specific Heat

• Specific Heat is the amount of heat, in joules,
  needed to raise the temperature of 1 gram of
  substance by 1 degree Celsius.
• Water has a high specific heat which means it
  must absorb or release a lot of heat to change
  the temperature just one degree.

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• This property is the reason why it takes a long
  time to heat the pool but it also takes a long
  time for it to cool.

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8. High Heat of Vaporization

• Heat of vaporization is the amount of heat needed
  to change the liquid to a gas.
• This happens when you sweat.

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9. Super solvent

• Many things can dissolve in water mainly because
  of its polar nature

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Water can dissolve ionic substances.

• Ionic compounds are formed when elements gain or
  lose electrons. There are positive ions and
  negative ions.
• When mixed in water, the ions undergo
  dissociation. The partly positive hydrogens
  surround the negative ions. The partly negative
  oxygen surround the positive ions.

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Water can dissolve polar covalent substances.

• Polar covalent substances are simply separated
  from each other in water. They do not dissociate
  into charged particles.

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Like dissolves like

• Water does not dissolve nonpolar covalent
  molecules.
• They are too unlike

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Solutions
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• A SOLUTION is a homogeneous mixture. It is the
  same throughout.

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• A solute is the substance being dissolved
• A solvent is the substance that dissolves the
  solute

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KOOL-AID

• What is the solute?
• What is the solvent?

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• More of a solid solute (like sugar) can be
  dissolved by
• Increasing the temperature of the solvent
• Heat up the water and more sugar will dissolve!

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Why do I use hot water when making coffee or tea?
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Temperature

• Temperature has a significant effect on
  solubility for most solid solutes.

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• More of a gas solute (like CO2 in your soda) can
  be dissolved by
• Decreasing the temperature of solvent
• Colder temperatures make more gas dissolve
• Increasing the pressure will also make more gas
  dissolve.
• That is why the lid is tight on your soda.

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How can I have a soda with lots of carbonation?
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Lose Pressure, lose Gas

• The higher the pressure, the more soluble the
  gas. (When the soda is opened, there is less
  pressure and the CO2 is now less soluble.)

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Heat it up, lose Gas

• The higher the temperature, the less soluble the
  gas. (Soda fizzes more when it is warm because
  the CO2 is not as soluble.)

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• Pressure does not affect the solubility of a
  solid

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Solutions

• Solutes can be made to dissolve faster in a
  solvent by
• Using a small particle size-crush it up
• Mixing-stir it up
• Increasing the temperature of the solvent- heat
  it up

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Solubility

• Solubility is the amount of solute that dissolves
  in a given quantity of a solvent at a given
  temperature

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Concentrated vs. Dilute

• A solution with a high concentration of solute is
  Concentrated
• A solution with a low concentration of solute is
  Dilute
• Do not use the words weak or strong. Those
  words refer to acids/bases (next chapter!)

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Unsaturated Solution

• If the amount of solute dissolved is less than
  the maximum that could be dissolved, the solution
  is unsaturated.
• You could still add more sugar and it would mix
  into the water

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Saturated Solution

• A solution that holds the maximum amount of
  solute per amount of solution under given
  conditions is saturated.
• If you add more sugar, it will just sit on the
  bottom of the cup. It will not mix in.

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Supersaturated Solution

• A solution that contains more dissolved solute
  than the usual maximum amount is a supersaturated
  solution.
• It cannot hold it permanently and may release it
  at any time. It is unstable.

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Freezing Point Depression

• A solution always has a lower freezing point than
  a pure solvent
• A solution of water and ?? (salt, sugar, ect.)
  will freeze at a temperature less than 0 degrees.
• Why do you add ice to ice cream to freeze it???

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Boiling Point Elevation

• The boiling point of a solution is higher than
  the boiling point of a pure solvent.
• Water and ?? (salt, ect) will boil higher than
  100 degrees.
• Why do you add salt to water before making
  macaroni?

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