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Water, Polar molecules, and an Intro to Solutions. Review of bond types. Review of bond types. Review of bond types. Polar Molecules. If a molecule contains polar covalent bonds, the entire molecule may have a positive end and a negative end.

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polar molecules
Polar Molecules
  • If a molecule contains polar covalent bonds, the entire molecule may have a positive end and a negative end.
  • This would then be classified as a polar molecule.
polar molecules1
Polar molecules
  • Not all molecules that contain polar covalent bonds are polar molecules.
  • This can be due to the shape of the molecule.
intermolecular forces
Intermolecular Forces
  • Van der Waals forces
    • Dipole dipole – attractive force between polar molecules
    • London dispersion force – attractive force between all molecules
slide10

Hydrogen bonds

  • A strong dipole-dipole force between a positive hydrogen atom of one molecule, and a highly electronegative atom (N, O, F) in another molecule.
water essential for life
Water: Essential for Life
  • 70% of the earth is covered in water yet only 3 % of it is fresh water and only 1 % of this is water is in a liquid state.
  • Canada has the most abundant supply of fresh water in the world but this doesn’t mean that we shouldn’t learn how to conserve water.
slide12

The water cycle is one method of natural purification. Energy from the sun causes water to evaporate, dissolved contaminants are left behind as it rises. When the water condenses it returns to earth as precipitation.

physical properties of water
Physical properties of water
  • Pure water is colourless, odourless, and tasteless.
  • Whether or not an object sinks or floats relates to its density compared to water.
    • Pure water density = 1.0 g / mL
slide15

Water is unique in the fact that its density decreases when it becomes a solid, this is what causes ice to float.

  • This in turn acts a blanket which prevents the water underneath from freezing and killing all life.
slide16

Heat capacity is a measure of how much heat it takes to heat one gram of a substance 1 ° C.

  • Water requires 4.18 J of heat to increase the temperature of 1 gram 1 ° C.
chemical properties of water
Chemical Properties of Water
  • Water is a polar molecule that consists of oxygen and hydrogen molecules. The oxygen has a larger electronegativity and so it creates a partial – charge as it draws hydrogen’s electrons closer to it.
  • Draw this
slide18

The large difference in charge allows for Hydrogen bonding to occur between molecules.

  • This provides water with its unique surface tension, high boiling point and ice that is less dense.
slide19

The polarity of water also allows water to dissolve other polar molecules.

      • Like dissolves Like– polar dissolves polar and non-polar dissolves non-polar
slide20

Ionic substances dissociate into charged ions when dissolved in water form electrolytic solutions – conduct electricity

  • Draw this
slide21

Substances that stay electronically neutral when dissolved in water are called nonelectrolytes.

  • Ex glucose
what s in polluted water
What’s in Polluted Water?
  • As the amount of human activity increases the amount of contaminants found in nearby water also increase. Contaminants are classified into three types.
1 physical contaminants
1. Physical Contaminants
  • Objects that do not dissolve in water.
    • Ex – oil, plastic, tree branches, leaves, peat, silt.
2 biological contaminants
2. Biological Contaminants
  • Biological contaminants include bacteria and viruses which may make the water unsafe to consume.
3 chemical contaminants
3. Chemical Contaminants
  • Chemicals that are soluble in water.
    • Ex – metal ions, pesticides, fertilizers.
  • These are not visible but can lead to visible effects such as an algae bloom
solutions
Solutions
  • Most substances contain water because it is so good at dissolving other substances.
  • AKA the “Universal Solvent”
    • Technically it is not universal because water does not dissolve non-polar substances. Only non-polar can dissolve non-polar.
  • All aqueous solutions use water as the solvent and are transparent.
slide28

A solution is a homogeneous mixtureof substances composed of at least onesoluteand one solvent that are uniform throughout the sample. This can be in a liquid or gas state.

slide29

Solute – A substance that is dissolved in a solvent

  • Solvent – The medium in which a solute is dissolved.
properties of aqueous solutions
Properties of Aqueous Solutions
  • Compounds can be classified as either electrolytes or non-electrolytes.
  • Electrolytes – solutes that form aqueous solutions that conduct electricity.
slide32

Most molecular compounds are nonelectrolytes, except for acids.

  • Solutions can also be classified as acids, bases, or neutral. These will be covered more in the next unit.
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