The Chemistry of Water

“If there is magic on this planet, it is contained in water.” --Loren Eiseley

“When the well’s dry; we know the worth of water” --Benjamin Franklin

Water’s polarity results in hydrogen bonding Water is a polar molecule Water is a polar molecule

The charge of the water molecules results in hydrogen bonds

The hydrogen bonding results in Cohesion—water to water Cohesion—water to water Adhesion—water to another substance Adhesion—water to another substance Surface Tension—how difficult it is to break the surface of a liquid Surface Tension—how difficult it is to break the surface of a liquid How do these properties relate to transpiration? How do these properties relate to transpiration?

Water moderates temperatures on earth Heat—TOTAL quantity of kinetic energy in a body of matter Heat—TOTAL quantity of kinetic energy in a body of matter Temperature—AVERAGE kinetic energy of the molecules Temperature—AVERAGE kinetic energy of the molecules Calorie—Amount of heat energy needed to raise 1 g of water 1º Celsius Calorie—Amount of heat energy needed to raise 1 g of water 1º Celsius

Water has a high specific heat Specific heat—amount of energy to cause 1 g of a substance to change its temperature by 1º C. Specific heat—amount of energy to cause 1 g of a substance to change its temperature by 1º C. Water’s specific heat is 1 cal/g/ºC Water’s specific heat is 1 cal/g/ºC The reason water’s specific heat is high is because a large amount of energy must be used to break the hydrogen bonds The reason water’s specific heat is high is because a large amount of energy must be used to break the hydrogen bonds

Areas surrounded by water have moderate temperatures—the water absorbs the heat—without raising the temperature of the water. Areas surrounded by water have moderate temperatures—the water absorbs the heat—without raising the temperature of the water. At night the loss of the heat by water warms the air. At night the loss of the heat by water warms the air. The result—the water itself and the surrounding land have a constant temperature The result—the water itself and the surrounding land have a constant temperature Water has a high specific heat

Water results in evaporative cooling Heat of vaporization—the amount of heat a liquid must absorb for 1 g to be converted from a liquid to a gas Heat of vaporization—the amount of heat a liquid must absorb for 1 g to be converted from a liquid to a gas This helps moderate earth’s climate This helps moderate earth’s climate As a liquid evaporates, the surface of the liquid that remains behind cools down. This is evaporative cooling. As a liquid evaporates, the surface of the liquid that remains behind cools down. This is evaporative cooling.

Stability of temperature in lakes and ponds? Stability of temperature in lakes and ponds? A mechanism that prevents terrestrial organisms from overheating? A mechanism that prevents terrestrial organisms from overheating? How does evaporative cooling result in

Ice Floats Water is at its densest at 4º C. From 4 º C to 0 º C, water expands Water is at its densest at 4º C. From 4 º C to 0 º C, water expands Subsequently, ice floats Subsequently, ice floats How is this an advantage for aquatic organisms? How is this an advantage for aquatic organisms?

Water is the solvent for life Reactions in cells take place in solution Reactions in cells take place in solution Solution—homogeneous mixture made of solute & solvent Solution—homogeneous mixture made of solute & solvent Water dissolves more substances than another other solvent Water dissolves more substances than another other solvent

Water is the solvent for life Because of water’s polarity, all ionic compounds, and polar covalent compounds (such as sugar) will dissolve in water Because of water’s polarity, all ionic compounds, and polar covalent compounds (such as sugar) will dissolve in water Hydrophilic—a substance that has an affinity (love) for water Hydrophilic—a substance that has an affinity (love) for water Hydrophobic—a substance that repels water Hydrophobic—a substance that repels water

Practice Free Response Water is a critical compound for the continuity of life. 70% of the earth’s surface is covered with water that is home to thousands of species. 70% – 90% of a cell’s (organism’s) mass is water. Water is a critical compound for the continuity of life. 70% of the earth’s surface is covered with water that is home to thousands of species. 70% – 90% of a cell’s (organism’s) mass is water. A. Discuss the chemical and molecular structure of the water molecule that uniquely enables it to support life on this planet. A. Discuss the chemical and molecular structure of the water molecule that uniquely enables it to support life on this planet. B. Describe three different contributions that water makes to life on earth. Explain how each contribution is related to the chemical structure of water. B. Describe three different contributions that water makes to life on earth. Explain how each contribution is related to the chemical structure of water.