Water & Solutions• Water is a unique molecule necessary

for life.• found in all cells and surrounds all cells

Polarity• an uneven distribution of shared

electrons within the molecule

Hydrogen Bonds• a weak chemical attraction between

polar molecules– the attraction between the positively

charged hydrogen of water and the negative charge that exists on other polar molecules including water itself

– due to water’s polarity

Cohesion and Adhesion• Cohesion

– attraction between molecules of the same substance

• Adhesion– attraction between molecules of different

substances

Water & Solutions

See Figure 5 on textbook page 31

Hydrogen Bonding in Water

Is this cohesion or adhesion?

Surface Tension• property of the surface of a liquid to resist

an external force– the surface can stretch and will not break

easily– caused by cohesion

Water & Solutions

Surface Tension

Capillary Action• process in which water molecules move up

through a narrow tube– the attraction of water to the walls of the tube

and to the other water molecules around it pulls the water up more strongly than gravity pulls it down

– caused by adhesion and cohesion

Water & SolutionsCapillary Action

Density• liquid water has a density of 1 g/mL

Solid form less Dense than Liquid form

• water is rare in that its solid form (ice) is less dense than its liquid form water

Solid form less Dense than Liquid Form

Solid form less Dense than Liquid form

• water is rare in that its solid form (ice) is less dense than its liquid form water– ice floats in water

Universal Solvent• “like dissolves like”• water is able to dissolve ionic compounds and

other polar compounds, but not nonpolar compounds

Universal Solvent• Solution

– mixture of two or more substances in which the solute molecules are evenly distributed in the solvent

• Solute– substance that is dissolved

• Solvent– substance that does the dissolving

Ionic vs. Polar vs. Nonpolar• Ionic

– substances made of oppositely charged ions held together by ionic bonds

• Polar– substances with charged ends held together by

covalent bonds• Nonpolar

– substances with no charges held together by covalent bonds

Water & Ionic SubstancesWhy is water able to dissolve salt?

Water & Ionic SubstancesSalt is ionic (made of charged particles) and water is polar (has charged ends).

Water & Polar SubstancesWhy is water able to dissolve sugar?

Water & Polar SubstancesSugar is polar (has charged ends) and

water is polar (has charged ends).

Water & Nonpolar Substances

Why does vegetable oil separate from water when they are mixed in the same container?

Water & Nonpolar Substances

Why does vegetable oil separate from water when they are mixed in the same container?

Vegetable oil is nonpolar (no charged ends), and water is polar (has charged ends).

Specific Heat• water has a high specific heat

– specific heat – the amount of heat required to raise 1 gram of a substance 1 degree Celsius

• it takes a lot of energy to heat up or cool down water

Water & Solutions• Pure water will ionize in the following

way to create hydrogen, and hydroxide ions.

• because of this, water has a neutral pH

H2O H+ + OH-

water hydrogenion

hydroxideion

Water & Solutions• pH - a system to measure the

concentration of H+ ions in a solution• Acids

– H+ > OH- – pH values < 7

• Bases– H+ < OH- – pH values > 7

• Neutral– H+ = OH- – pH values = 7– pure (distilled) water

Water & Solutions

Water & Solutions• each whole number represents a factor

of 10 on the scale– Ex: A solution with a pH of 5 is 10 times

as many hydrogen ions as one with a pH of 6

– Ex: How much more acidic is a solution with a pH is 2 than one with a pH is 5?• 2 3 = 10 times• 3 4 = 10 times• 4 5 = 10 times• 10x10x10 = 1,000 times more acidic!

Water & Solutions

Water & Solutions• Buffers

– Weak acids or bases that prevent sudden changes in pH in living organisms