Its About Water notes
schmied/reid©2007 all rights reserved
Part One (new 2007)Why life would not exist on Earth as we know it without good ole H2O.
• Water has a wide spread between its boiling point (evaporation/condensation) and freezing point (melting/freezing). These "bracket" living systems on Earth. If the difference were smaller between the two, all life on Earth would be affected.• Water is a Polar Molecule. H2O has a weak positive charge on one side (Hydrogen side) of the molecule, and a weak negative charge (Oxygen side) of the molecule. This gives the water molecule unique abilities... and allows it to hold together (cohesiveness) and also to hold on to other substances (adhesiveness).
• Cohesion = when like molecules stick together (water to water)
• Adhesion = when unlike molecules stick together (water to root etc)
• Water is less dense as a solid than as a liquid. Thus ice floats. If it didn't all bodies of water might eventually freeze from the bottom up!
• Most living things are mainly made of water.
Part Two: Make up of Water Molecules:
• Chemistry
Go to Periodic table in your planner Review 114 elements, 88 naturally occuring
- All other elements want to be Noble! (Have all electron shells filled)
(Outer shell only one important for making molecules because inner shells get filled in first!)
Cohesion in chemistry is the intermolecular attraction between like-molecules. Cohesion explains phenomena such as surface tension. Cohesion is produced by the intermolecular forces. Capillary action for example described in the Cohesion-tension theory related to botany is considered a mix of cohesion and adhesion.
Adhesion is the molecular attraction exerted between bodies in contact, often not similar. It is of particular interest to engineers who wish to stick things together and to biologists to understand the workings of cells.
Properties of Water Demos
•Bend water - Show water has an electric charge. Bending a water column provides visual evidence to this idea!
•Surface search - Look at the surface of the water column in beakers, flasks, graduated cylinders. Describe and draw what you see. Label where the water is showing cohesion, adhesion. Tell what it is called...
•Water Drop - Slowly drop water drops out of a dropping pipet. Describe and draw the water as it looks before dropping off and while free falling. Label where the water is showing cohesion and adhesion.
•Cork drop - Place a cork in the exact center of a water column so that it will stay in the exact center. Describe and draw what happened when you did this.... why? Find a way to make it stay in the exact center. Describe and draw what this looks like. Label where adhesion and cohesion occur.
•Needle float - Carefully place a needle on the surface of the water. Draw and describe what you see. Is this cohesion, or adhesion
•Capillary Tube - Draw what happens when you put and hollow glass tube into water.... is this cohesion, or adhesion, or both? Take tubes out of water and describe again!
•Water down a rope - Describe how water can travel down a wet string long distances... is this cohesion or adhesion or both?
•Put money in completely filled glasses fitted together. Fill one glass completely full. Fill the other and place index card on top. Flip glass, place on top of first full glass and carefully pull out card. Show how you can put a dime, penney, nickel, or quarter into the sealed glasses without spilling all the water out. Why can you do this?
Show how to read a Graduated Cylinder...... eye level with meniscus, read the bottom...... tell why the bottom of the meniscus is best to read using precision, accuracy, and error in explanation.
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