Section 2 Water and Solutions Chapter 2 Section 2 Water and Solutions Grade 10 Biology Fall 2010

Bell Ringer http://www.youtube.com/watch?v=orW7CEwcAW8 List some common acids and bases Why do you think water is such an essential compound?

Objectives Analyze the properties of water Describe how water dissolves substances Distinguish between acids and bases

Water in Living Things 70 percent of your body is made of water About two-thirds of the molecules in your body are water molecules Water is the medium in which most cellular events take place

Storage of Energy Water absorbs heat more slowly and retains this energy longer than many other substances do Many organisms release excess heat through water evaporation Ex. Sweating In organisms, the ability to control temp. enables cells to maintain a constant internal temp. when the external temp. changes Homeostasis

Cohesion and Adhesion Hydrogen bonds between molecules cause the cohesion of liquid water Cohesion: an attraction between substances of the same kind Molecules at the surface of water are linked together by hydrogen bonds This attraction between water molecules causes a condition known as surface tension

Cohesion and Adhesion Water molecules are attracted to similarly polar substances Adhesion: an attraction between different substances Adhesion powers process called capillary action

Cohesion and Adhesion

Aqueous Solutions Solution: a mixture in which one or more substances are evenly distributed in another substance Many important substances in the body have been dissolved in blood or other aqueous fluids Because these substances can dissolve in water, they can more easily move within and between cells

Polarity The polarity of water enables many substances to dissolve in water Water is a polar substance

Polarity Ionic compounds and polar molecules dissolve best in water Why? When dissolved in water ions become surrounded by polar water molecules Ions are attracted to the ends of water molecules with the opposite charge, solution is mixture of water molecules and ions Similar attraction results with polar molecules Ions or molecules become evenly distributed in water

Polarity Non-polar molecules do not dissolve well in water Why? When non-polar substances are placed in water, the water molecules are more attracted to themselves than the non-polar molecules Result is the non-polar molecules are shoved together

Acids Acids: compounds that form hydrogen ions when dissolved in water When an acid is added to water, the concentration of hydrogen ions in the solution is increased above that of pure water Hydrogen ion = H+ Acidic compounds have a pH value less than 7

Bases Base: compounds that reduce the concentration of hydrogen ions in a solution Many bases form hydroxide ions when dissolved in water Hydroxide ion = OH- Basic compounds have a pH value greater than 7

pH pH scale: based on the concentration of hydrogen ions in solution All solutions have a pH value between 0 and 14 Each whole number represents a factor of 10 A solution with a pH value of 5, has 10 times as many hydrogen ions as one with a pH value of 6

Review T/F Non-polar molecules dissolve very easily in water. T/F Cohesion and adhesion of water molecules help a plant move water from its roots to its leaves. T/F When a base is added to water, the concentration of hydrogen ions increases. T/F A substance has a pH value of 11 therefore it is basic.

Answer F: Non-polar molecules dissolve very easily in water. T: Cohesion and adhesion of water molecules help a plant move water from its roots to its leaves. F: When a base is added to water, the concentration of hydrogen ions increases. T: A substance has a pH value of 11 therefore it is basic.