Water Lab Olympics

Water's History:  (must be read aloud with a deep announcer-style voice)... When life on Earth was beginning between 3 and 4 billion years ago, water provided a medium in which other molecules could interact.  Life as we know it could not have evolved without these interactions.  Today, 3/4 of Earth's surface is covered by water.  Every cell in your body contains water.  In most cells there is an abundance of it; about 2/3 of the molecules in your body are water molecules. 

Water heats more slowly than most other substances.  It also retains its temperature longer than other substances when its surrounding environment cools - it store heat well.  This keeps the temperature of areas surrounding large water bodies more stable throughout the changing seasons.  Many organisms dispose of excess heat through water evaporation.  For example, humans cool down by sweating.

Water molecules readily form special bonds, called hydrogen bonds, with one another, so water clings to itself in an attraction called cohesion. (vocab word) It is because of cohesion that water is a liquid and not a gas at room temperature.  Hydrogen bonds link many individual water molecules together at the water's surface, like a crowd of people linked by holding hands.  Surface tension (vocab word) forms across the surface of water because of the cohesive attraction between individual water molecules.  The attraction of water to a substance other than water is called adhesion. (vocab word) Water adheres to any substance that it can form hydrogen bonds with (the substance is thus called hydrophilic (vocab word), "water loving").  Polarized molecules (that have a separation of + and - charges) will also form hydrogen bonds and are hydrophilic.  Hydrophilic substances will mix with water; such as, water and vinegar mix together because vinegar is polar and therefore hydrophilic.  That is why some things get "wet" and others, such as waxy substances, that are composed of non-polar molecules, do not (these substances are called hydrophobic (vocab word), "water hating").  The feathers on a duck are coated with a special non-polar waxy substance so the water forms droplets that roll, literally, right off the duck's back. Hydrophobic substances do not mix with water. 

The adhesion of water to substances with surface charges causes capillary action (vocab word).  Capillary action and cohesion are responsible for the upward movement of water.  For example, in plants, water moves upward from the roots, travels through the vascular system and, finally, exits through the leaves.  Adhesion is also responsible for the meniscus present in liquids that are measured in a graduated cylinder.

Procedure: 

1. Vocab:  List and define all vocab words from the reading.  Underline the vocab word.  There are six.

2.  Read the directions for each event and place all responses in notebook:

Event #1: Demonstrate the adhesion/cohesion property of water, as well as surface tension.

1.  Fill a glass with water and float a dry needle on the surface.  You may need to use forceps/tweezers to aid in the success of this event.  Don't get too frustrated by this...if you haven't had success after 5 tries, stop, write that down and explain why the needle kept breaking the surface.

    a.  Record the time it took you to complete this task. 

    b.  After making close observations (if you have a magnifying glass, use it)  write down 3 observations about the floating needle.

    c.  Why does it help to have the needle be dry?

    d.  Which part of the activity demonstrated adhesion?  Why?  Which part of the activity demonstrated cohesion?  Why?

2. Obtain a clean, dry penny; set on table.  Slowly drop water on its surface until the water spills over. 

    a.  Record how many drops of water you added? 

    b. What did the water look like on the penny before it spilled over?

    c.  Why were you able to get so many drops of water on the penny?  Think about the vocab words.

    d.  Why did the water eventually spill over?  (in other words, why couldn't an endless supply of water drops be added to the penny?)

Event #2: Slip-n-slide: Demonstrate the hydrophobic properties of oil.

1.  Mix one cup water and one tablespoon oil together in a dry, clean glass.  Stir with a utensil.  Let the mixture sit for about 2 minutes.

    a.  Do the water and oil combine?     

    b.  Is oil hydrophilic or hydrophobic?  How do you know?

Event #3: Demonstrate the hydrophilic properties of detergent:  Detergent is composed of fatty acids in association with positively charged ions (cations) such as Na+ and K+.  These associations, called "soaps of fatty acids," are polar. 

1.   Mix one cup water and one tablespoon detergent (laundry, dish or hand soap).  Stir with a utensil.  Let the mixture sit for about 2 minutes. 

    a.  Do the water and detergent combine?  

    b.  Is detergent hydrophilic or hydrophobic?  How do you know?

Event #4:  Demonstrate the dissolving abilities of hydrophilic vs. hydrophobic substances.

1.  Add 1 tablespoon of oil to a small dry, clean glass.  Pour a pinch  of salt or sugar.  Mix for one minute with a toothpick  Let sit for a few minutes:  stir the contents again for 30 seconds before observing.

    a.  Does the salt or sugar dissolve in the oil?

    b.  Is oil polar or non-polar? 

    c.  Is oil hydrophilic or hydrophobic? 

2.  Add 1 tablespoon of water to a small dry, clean glass.  Pour in one pinch of salt or sugar.  Mix for one minute with a toothpick. Let sit for a few minutes:  stir the contents again for 30 seconds before observing.

    a.  Does the salt or sugar dissolve in the water?

    b.  Is water polar or non-polar? 

    c.  Is water hydrophilic or hydrophobic? 

    d.  What generalizations can be made about polar/non-polar substances and whether they are hydrophilic or hydrophobic?