Day 3: Water

Today we learnt all about water.

We each got to choose a number to explain one of the aspects of Question 10 in the Unit 1 objectives.

Tanya and I answered: Why is a water strider able to walk on the surface of a pond without breaking the surface?

The answer to this question was a water strider is able to walk on the surface of the pond because water has a high surface tension because the molecules have a lot of cohesion. The cohesion is in the attachment of the hydrogen bonds, and the water strider can stand on the strong bond attractions, without breaking it. We learnt additionally to this answer we proposed, that the water strider's legs have a large surface area. The larger the surface area the more spread out the weight is.

The previous first questions were on: Why Coastal areas have milder climates than adjacent inland areas? or Why Ocean temperatures fluctuate much less than air temperatures on land? are very similar. Both of them are to do with molecular motion. Hydrogen bonds have the ability to move and break and reform. This ability causes the temperatures to go up on land when they break. Then down when the bonds reform. Soil also doesn't have any hydrogen bonds so can't regulate temperatures as well as oceans.

The fourth question explained was:   If you slightly overfill a water glass, the water will form a convex surface above the top of the glass. This is because the cohesion between the water molecules pulls them together above the glass because there is no longer any adhesion. It is convex because the angle of bent H2O molecules are 109.5 a large angle. 

The fifth statement to explain was:   If you place a paper towel so that it touches spilled water, the towel will draw in the water. This is because water molecules have a weak inter attraction (cohesion) compared to it’s attraction to another substance (adhesion), this is because of the hydrogen bonds. So the molecules of water adhere to the air pockets in the towel. 

The last statement that was explained to us is: Ice floating on Water. Ice floats on water because when water is liquid there is lots of motion and molecules can keep moving. When it is ice however, there is little motion in a solid and then there are pockets of air. The ice is then less dense and can float on the water. 

After listening to everyone explain their questions, larger groups were formed to answer questions about sweat. We sweat and dogs pant to shed excess heat. We can do this because water has a high heat of vaporization, so we use a lot of energy to vaporize the water molecules into the air. If it is humid however there are already water molecules in the air so it is harder to add ours and get rid of our sweat (in the form of vapor molecules).


We also did an experiment with a penny that should surface tension in water. We then learnt that surfectants (like soap) are substances that can break hydrogen bonds and the surface tension.

Red Cabbage has a pigment molecule called flavin which is an anthocyanin. Very acidic solutions will turn these pigment molecules into a red color. Neutral solutions will turn the pigment a purplish blue. Very basic solutions will turn the pigment a greenish yellow. The color of the juice reacts to the hydrogen and whether or not it donates or accepts a hydrogen ion. Acid rain would affect the growth of cabbage and increase it because more cabbages would become red. But eventually it would affect the development long term because increased exposure to acid rain is harmful to any living thing.