Saturday, November 17, 2012

Adhesion...another water experiment

 As you may remember, we've been studying water... water molecules, hydrogen bonding...etc.  Wednesday, we did more experiments.  First, I gave each pair a clear plastic cup with water in it.  Then I came around with a bucket and they poured the water out...then observed the plastic cup.

What did they observe?  Even though the water was poured out, some stuck to the sides of the cup.  Why didn't it all pour out? 
 Next, each group got a square of wax paper, an eye dropper, and more water in their cup.
 They were to put a few drops of water on the wax paper....
 They were then given a toothpick...
 and instructed to try and move around the drops of water.
What did you observe?  
 We got a variety of answers.  Some said when the water drop moved, the wax paper underneath was dry.
Others said when the drops got together, they made larger drops... some said when a drop got close to another drop, it was attracted to it...
Why????

 We collected the eye droppers and passed out straws.  The next experiment was to put the end of the straw about a centimeter or two into the water... put your finger over the top of the straw, then pull the straw up, but not completely out of the water. 
 They were to observe the SHAPE of the water INSIDE the straw...and draw it. 
 Ahhh, the power of observation!  As I walked around, many had just drawn a straight line for the top of the water in the straw.

"Carefully observe!" I said.

"I am!"

"No, look again."
 "Oh, Mrs. Johnston!  Look!  Is this what I'm suppose to see?"

Some eyes were really looking at the shape!
Ian...for your information...is not napping.  He's carefully looking at the shape of the water.  
 Do you know what the shape was?
 It was concave...

WHY???
At that point, lightbulbs started going off in Room 5.  All the experiments were coming together looking at water in a straw...but the bottom of the straw had to be in the water...and the top of the straw had to have a finger over it.

What happened?  Why was it concave?  Room 5ers accurately talked of hydrogen bonding...between the water in the straw and the water in the cup... adhesion of the water molecules against the side of the cup was like the adhesion of the water molecules on the sides of the straw.  The water in the cup was like it was 'pulling' (attracting...hydrogen bonding) the water from the straw down toward the cup.  Since the water HAD BEEN higher in the straw before we pulled it out a little, the water was adhering (adhesion) to the sides of the straw since it still had water molecules on it....thus, we had a concave shape of the water.

"Water is fun!" I heard....

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