lesson 3: cohesion, adhesion & surface tension

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Lesson 3: Cohesion, adhesion & surface tension Objective: 1. Describe cohesion, adhesion and surface tension 2. Understand how and why plants utilize them.

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Lesson 3: Cohesion, adhesion & surface tension. Objective: Describe cohesion, adhesion and surface tension Understand how and why plants utilize them. How many drops of water fit on a penny?. Part A Rinse a penny in tap water and dry completely Place the penny on a paper towel - PowerPoint PPT Presentation

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Page 1: Lesson 3:   Cohesion, adhesion & surface tension

Lesson 3: Cohesion, adhesion & surface tension

Objective:1. Describe cohesion, adhesion and surface

tension2. Understand how and why plants utilize

them.

Page 2: Lesson 3:   Cohesion, adhesion & surface tension

How many drops of water fit on a penny?

Part A1. Rinse a penny in tap water and dry completely2. Place the penny on a paper towel3. Use a dropper to place DROPS of WATER on the penny

(one at a time) until ANY amount of water runs over the edge of the penny.

4. Record the number of drops for the trial in the table.

Trial #1 Trial #2 Trial #3 Trial #4 Average

Page 3: Lesson 3:   Cohesion, adhesion & surface tension

Part B

1. Clean the penny. Rinse the penny in tap water and dry completely. Try to remove as much residue as possible – WITHOUT soap.

2. With tweezers, dip the penny into the testing liquid. Let extra liquid drip off the penny into the beaker.

3. Place the penny on a dry paper towel. Place drops of WATER on the penny (one at a time) until ANY amount of water runs over the edge.

Page 4: Lesson 3:   Cohesion, adhesion & surface tension

ReviewIonic BondingIonic bonds form when electrons are transferred from one atom to another. Example: salt NaCl

Covalent BondingCovalent bonds result when two atoms share electrons so each atom has octet of electrons in the outer shell. Ex. Chlorine Cl2

Page 5: Lesson 3:   Cohesion, adhesion & surface tension

Polar and Nonpolar bonds* ONLY covalent bonds can be polar/ nonpolar

PolarPolar covalent bonds: the sharing of electrons is unequal.•  In a water molecule, each hydrogen atom has a partial

positive charge and the oxygen atom has a partial negative charges.

NonpolarNonpolar covalent bonds: sharing of electrons is equal. • They do not interact with polar molecules.• Example Oil and ethane

Page 6: Lesson 3:   Cohesion, adhesion & surface tension

What will happen when two water molecules bump into each other?

• When the oxygen atoms of 2 different water molecules come together, they repel.

• When the hydrogen atoms of 2 different water molecules come together, they repel.

• When an oxygen atom and a hydrogen atom from two different water molecules come together, they attract

Page 7: Lesson 3:   Cohesion, adhesion & surface tension

Adhesion and Cohesion

• The attraction between two like molecules is cohesion.

• The attraction between two unlike molecules is adhesion.

• Adhesion and cohesion are intermolecular forces between two molecules.

Page 8: Lesson 3:   Cohesion, adhesion & surface tension

Surface tension• Adhesion between water and glass leads to

capillary rise in a glass tube. Water and glass have a smaller attractive force compared to water’s attraction of water.

The cohesive force of water molecules is responsible for the phenomenon of surface tension. Water molecules have a strong mutual attraction for one another, enabling them to hold together strongly.

Page 9: Lesson 3:   Cohesion, adhesion & surface tension

Capillary action in plants

Capillary action in plants is a good example of adhesion and cohesion.

The inner surface of the xylem (the cell wall of a plant) contains positive and negative charges to which water forms hydrogen bonds. This is called adhesion.

As water creeps up the sides of the xylem (adhesion) the water molecules in the middle connect to other water molecules because of cohesion.

The water moves up as the water molecules at the top of the xylem enter the leaves and evaporate (move out of the stomata in the leaf). When a water molecule leaves the leaf, the molecule behind it moves up causing a general movement of the water up the tree.