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2-2 Properties of Water
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2-2 Properties of Water
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The Water Molecule
The Water Molecule
Water is the single most abundant compound on earth – 75% of the earth is covered in water.
Water is the most abundant compound in living things – about 70% by mass in living things.
Like all molecules, a water molecule is neutral.
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The Water Molecule
Water is a polar molecule
A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms.
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The Water Molecule
Hydrogen Bonds
Because of their partial positive and negative charges, polar molecules can attract each other.
This is a type of Van der Waals force.
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The Water Molecule
Hydrogen bonds are not as strong as covalent or ionic bonds
Water’s ability to form multiple hydrogen bonds is responsible for many of its special properties.
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The Water Molecule
Hydrogen bonds form between water molecules.
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The Water Molecule
Cohesion is an attraction between molecules of the same substance.
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The Water Molecule
Water's cohesion causes molecules on the surface of water to be drawn inward, which is why drops of water form beads on a smooth surface.
Cohesion also explains why
some insects and spiders
can walk on a pond's
surface.
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The Water Molecule
Adhesion is an attraction between molecules of different substances.
Capillary action only occurs when the adhesive forces are stronger than the cohesive forces.
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The Water Molecule
Adhesion between water and glass causes water to rise in a narrow tube against the force of gravity.
This effect is called capillary action.
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The Water Molecule
Capillary action is one of the forces that draw water out of the roots of a plant and up into its stems and leaves.
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The Properties of Water
• Water expands when it freezes – causing erosion, weathering and formation of soil
• Water is less dense when frozen – allowing ice to float on the top of lakes and ponds so that living things are still able to survive underneath.
• Water resists temperature changes – aiding in homeostasis
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Solutions and Suspensions
Solutions and Suspensions
A mixture is a material composed of two or more elements or compounds that are physically mixed but not chemically combined.
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Solutions and Suspensions
Two types of mixtures can be made with water
• solutions
• suspensions
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Solutions and Suspensions
Solutions
All the components of a solution are evenly distributed throughout the solution.
In a salt–water solution, table salt is the solute—the substance that is dissolved.
Water is the solvent—the substance in which the solute dissolves.
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Solutions and Suspensions
When a crystal of table salt is placed in warm water, sodium and chloride ions are attracted to the polar water molecules.
Na+
Na+
Cl -
Cl -
WaterWater
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Solutions and Suspensions
Ions break away from the crystal and are surrounded by water molecules.
Na+
Na+
Cl -
Cl -
WaterWater
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Solutions and Suspensions
The ions gradually become dispersed in the water, forming a solution.
Na+
Na+
Cl -
Cl -
WaterWater
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Solutions and Suspensions
Water's polarity gives it the ability to dissolve both ionic compounds and other polar molecules, such as sugar.
Water is the greatest solvent on Earth.
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Solutions and Suspensions
Suspensions
Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out.
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Solutions and Suspensions
The movement of water molecules keeps the small particles suspended.
Such mixtures of water and nondissolved material are known as suspensions.
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Solutions and Suspensions
Some of the most important biological fluids are both solutions and suspensions.
The blood that circulates through your body is mostly water, which contains many dissolved compounds.
Blood also contains cells and other undissolved particles that remain in suspension as the blood moves through the body.
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