Water Chemistry

Organic Versus Inorganic Organic compounds are those generally derived from living organisms (sugar, protein, etc) Inorganic compounds are those generally derived from non-living sources (Ex: water) Both are important to life

Properties of Water

Points to ponder How does water rise from the roots of a redwood tree to the very top? How do insects walk on water? Why does ice float rather than sink? Why do people become seriously ill, or die, if they go without liquid for a week or so? How would life in a lake be affected if ice sank and lakes froze from the bottom up?

Water is the most important inorganic molecule to living things. Water makes up 50 to 95% of all living things. It covers 3/4 of the Earth's surface

Water is polar,unevenly charged. –The oxygen atom has a partial negative charge –The hydrogen atoms have a partial positive charge. –This is important because the charges make water a very effective solvent. (AKA the “Universal Solvent”) (AKA the “Universal Solvent”)

Polarity of Water O HH - + +

Hydrogen Bonds Polar water molecules act like magnets and attract each other Hydrogen Bonds –The attraction of the Hydrogen end (+) of one molecule for the Oxygen end (-) of another water molecule. They are strong bonds that form between molecules (CO 2, H 2 O, …)

Adhesion This property of water allows water to "adhere" to other substances, such as paper. –Plants use this property to get water from the roots to the leaves this is called capillary movement.

Cohesion This is water molecules "cohering" to each other. This occurs through hydrogen bonds. "cohering"

Cohesion This property is why water takes so long to heat up and cool down (a watched pot never boils) This is important so the cells can stay at a even temperature even in a variable environment. This also accounts for the surface tension of water

Cohesion = Surface Tension

Solutions & Suspensions Water is usually part of a mixture. Because so many things dissolve in water, it is called the Universal Solvent There are two types of mixtures: –Solutions –Suspensions

Properties of Solutions Ionic compounds disperse as ions in water (+ions & -ions spread out among polar water molecules) Solutions are evenly distributed mixtures SOLUTE –Substance that is being dissolved SOLVENT –Dissolving Substance for the solute

Ionic Solutions Na+ ions will be attracted to WHAT END of the water molecule?

Why did we add salt to make our slushies ? When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt. This makes the ice colder than it was before, which is how your slushy freezes. Salt also raises the boiling point of water, making things like pasta cook slightly faster.

Suspensions Substances that don’t dissolve but separate into tiny pieces. Water keeps the pieces suspended so they don’t settle out. Blood & Cytoplasm are suspensions

Points to ponder Revisited How does water rise from the roots of a redwood tree to the very top? How do insects walk on water? Why does ice float rather than sink? Why do people become seriously ill, or die, if they go without liquid for a week or so? How would life in a lake be affected if ice sank and lakes froze from the bottom up?

Additional Water Information Water freezes at 0°C (32°F) and boils at 100°C (212°F). 1 gallon of water weighs about 8 pounds. Water is unique in that it is the only natural substance that is found in all three states -- liquid, solid (ice), and gas (steam) -- at the temperatures normally found on Earth Water is unique in that it is the only natural substance that is found in all three states -- liquid, solid (ice), and gas (steam) -- at the temperatures normally found on Earth “Hard water” contains a lot of dissolved minerals like calcium and magnesium and makes soap less sudsy.