Cohesion and Adhesion (David Bird)

Title: Cohesion and Adhesion

Principle(s) Investigated: Cohesion, adhesion, polarity, polar molecules, surface tension, covalent bonds, hydrogen bonds.

Materials:

1) Plastic Pipet

2) Penny

3) Jar of water

4) Paper Towel

Procedure:

Cohesion Penny Game!

Get into groups. You need one penny, a pipet, a paper towel, and a beaker of water. Set the penny (Lincoln up) on the paper towel. Now add drops of water from the pipet, one drop at a time. Try and fit as many drops of water as you can on top of the penny without it spilling over. The team that fits the most drops of water on top of the penny wins.

Enter your values in the Quickwrite

Student prior knowledge: No prior knowledge needed

Questions & Answers:

Q: How is it that a tree that is 10m tall is able to bring water up to its leaves? Remember that trees do not have any muscles

A: The leaves of the tree allow water vapor to leave through pores called stomata. As the water vapor escapes the water molecules pull the water molecules behind it (through cohesion). As the water molecules are pulled up by the escaping water molecules this creates a chain reaction all the way down to the roots. So the tree has to lose water to gain water.

Q: Why does a belly flop hurt? Why is it that you can easily slide your hand into water but if you slap it you can not break the surface?

A: Because of the hydrogen bonds of water a surface tension is created. This is the same principle as cohesion. The water does not want to let go of itself. When you slide your hand into the water you are pushing the hydrogen bonds apart but when you slap the water you are hitting the bonds before they get separated.

Q: how does a gas lantern work when the wick is above the fuel?

A: Because the wick is sitting in the fuel the fuel climbs the wick the same way water climbs a paper towel.

Applications to Everyday Life:

We can see the principles of cohesion and adhesion when we clean up water with a paper towel. The water will climb the paper towel. The water does this because of the adhesion of the water to the paper towel and the cohesion of the water to other water molecules

Water!

Water has many amazing properties that allow life on this earth possible. If water did not have the structure it does we would not exist!

Polar molecule- A molecule having a positive end and a negative end

-When water molecules stick to other water molecules it is called a hydrogen bond.

-Hydrogen Bond = When the positive ends of hydrogen stick to the negative end of oxygen. Hydrogen bonds are very weak.

-Cohesion = Water sticking to water because of the hydrogen bonds

-Cohesion causes surface tension which is the waters surface resisting being broken

Example of surface tension is a belly flop!

How can you run on water?

-Adhesion = water sticking to other molecules other than water

Cohesion Penny Game!

Get into groups. You need one penny, a pipet, a paper towel, and a beaker of water. Set the penny (Lincoln up) on the paper towel. Now add drops of water from the pipet, one drop at a time. Try and fit as many drops of water as you can on top of the penny without it spilling over. The team that fits the most drops of water on top of the penny wins.

The bubble that the water created over the edge of the penny was a good example of cohesion. The water did not want to spill over because the hydrogen bonds where holding the water molecules to each other.

-Water is a polar molecule giving it many important features

-The most important feature of water is that it is less dense in its solid form than its liquid form

-Three states of matter

-Solid

-Liquid

-Gas

-Ice floats because water is more dense than ice

-Ice is 10% less dense than water so only 10% of ice breaches the water

-Since ice floats it is the surface of the ocean that freezes. The sheet of frozen ocean that forms insulates the water underneath which allows organisms to continue thriving under the ice without freezing.

Clouds have mass. They have a weight. That is why they can only float so high. The denser the cloud the lower it will float

High specific heat

-Because the water molecules are attracted to each other in a hydrogen bond it takes a lot of energy to break them apart. The hydrogen bonds need to be broken in order for water to change state...ice-water-steam

-This is referred to as high specific heat

-Water's high specific heat is important for many reasons. Many marine organisms need to maintain a consistent body temperature. Since it takes a large amount of energy to change the temperature of water the ocean's temperature changes subtly.

Water as a solvent

Because of water's polarity it makes a perfect solvent. It pulls ions apart separating them from their ionic bonds. This is why things dissolve in water.