Chemistry of Water Are you thirsty yet? You will be…

Fun Fact! 75% of the Earth is covered by water The rest is covered by Troy Polamalu

Water Molecules Composed of 2 Hydrogen atoms and 1 oxygen atom covalently bonded (H 2 O) Electrons stay with Oxygen more which leads to polarity Polarity = molecule has a positive (H) end and a negative end (O) Polarity gives water unique properties

Hydrogen Bonding = Negative (Oxygen) pole of a water molecule is attracted to the positive (Hydrogen) pole of another water molecule It is a weak attraction but does give water some cool properties Molecules that are not polar will not experience hydrogen bonding

Thirsty Yet?

Some unique properties of water 1)High Boiling Point = 100 o C (212 o F) 2)Solid form is less dense than liquid form (ice floats in liquid water) 3) Cohesion = water molecules wanting to stay together, keeps water in puddles instead of widespread droplets or molecules 4) Adhesion = water molecules wanting to stay connected to other polar surfaces (glass)

More unique properties of water Capillary action = water rising on its own up through a thin column Combination of adhesion attracting water molecules to the side of the column and cohesion pulling more water up into the column Glass tubes and plant roots are good examples

Make it Happen 1) get a partner 2) get a dish and a capillary tube 3) get some water in the dish 4) add food coloring to water 5) show your teacher capillary action using the tube

Water can be part of mixtures Mixture = a combination of pure substances occupying the same space (physically mixed but not chemically bonded) Ex. Air is a mixture of gases (oxygen, carbon dioxide, nitrogen, etc…) Water can dissolve other substances into it to create a solution Water is the solvent The dissolved substance is the solute Salt water is a good example

Other types of mixtures Suspensions = a solid settles in a liquid, does not dissolve Sand in water Blood is a combination of a solution and a suspension It contains cells (not dissolved) and other dissolved substances like sugar

Polarity of Substances “Like dissolves like” Polar liquids dissolve other polar liquids Polar liquids will not mix with non-polar substances (i.e. – oil & water don’t mix) Substances that repel water = hydrophobic Substances attracted to water = hydrophilic

Is it dry in here?

pH of solutions pH describes the concentration of H+ ions in a solution (acidity) Water has a fairly neutral pH because not many of its molecules lose a hydrogen ion Some solutions have an abundance of H+ ions and are called acids Some solutions have a lack of H+ ions (or abundance of OH-) and are called bases

pH scale Scale extends from 1 to = acid (acidic) 8-14 = base (basic or alkaline) 7 = neutral Buffers = weak acids or bases that can be used to balance out strong changes in pH Our bodies use buffer chemicals to maintain a balanced pH

pH Scale What could you ingest for an upset stomach? Why does it work?

pH Indicators Litmus paper Red = acidic, blue = basic pH paper Different colors correspond to a specific pH Cabbage juice – similar reaction as pH paper

Who wants a drink?