Properties of Water. Water The universal solvent in living things which makes up over 90% of cells and the majority of Earth.

Properties of Water

Water

The universal solvent in living things which makes up over 90% of cells and the majority of

Earth

Why water works well in living things

1. Water is Polar and is really good at dissolving substances

2. Water is needed for all cellular chemistry3. Water molecules adhere to some things4. Water molecules stick together5. Water molecules form surface tension6. Ice floats7. Water has a high specific heat

Some substances adhere to water, others are repelled

• Hydrophilic means water molecules are attracted to this substance– “Water Loving”

• Hydrophobic means water molecules are repelled from this substance– “Water Fearing”

Universal solvent

• Water is a solvent (it dissolves stuff for living things)

• Water can dissociate (break apart) most ionic compounds such as salts.

• Solutes + Solvent = Solutions

Reflection Writing

• Why do we look for water on other planets like Mars?

Water molecules are Polar

• 2 hydrogen + 1 oxygen (H2O)• = delta = slightly

O

H H++

-

Polarity

• Water molecules are polar.

• Polarity: one end of molecule positively (+) charged and other end negatively (-) charged

• Polarity causes hydrogen bonding between water molecules

Hydrogen Bonding• Weak bonds between a

hydrogen of one molecule to an adjacent negative molecule

• Ex: attraction between water molecules.

Drawing of a water molecule indicating the charges.

• Water molecules are attracted to each other.

• Water molecules “stick” together.

Cohesion

Hydrogen Bonds

Cohesion causes Surface Tension

• Surface Tension• Water molecules tend

to stick together, forming a sort of “skin”

• Some animals can use this “skin” as surface on which it can walk.

Water strider spider

Surface Tension

• What properties of water makes a belly flop hurt so bad?

• http://www.youtube.com/watch?v=N8gavevFX-0&feature=fvsr

Adhesion• Water molecules stick to

other molecules (not water)

• Water molecules are attracted to surfaces that have charges (hydrophilic).

• Water molecules are repelled from surfaces that have no charge (hydrophobic).

Capillary action in Plants

Density

• Water becomes less dense (more space between molecules) when it freezes.

DensityHow does DENSITY affect ecosystems?• Ice floats, creating buffer from cold air,

enabling organisms to still survive underneath the frozen surface.

Properties of Water Lab

• What are the properties of water that make it important for life?

• Why do all living cells require water?• Why is water called the universal solvent?

Surfactants

• Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid.

• Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants.

• Why are surfactants used in an automatic dishwasher?

Properties of Water Lab1. Use your Notes & Discussion from powerpoint2. After notes and discussion on the properties of water, write

a hypothesis about how many drops of water you should be able to fit onto a penny

3. Each groups does 5 trials4. Average the results and put them on the class data table5. Copy data from class data table6. Calculate the % error7. Create a bar graph of the data.8. Answer the conclusion questions on your lab sheet

Water Lab

Acids, Bases & pH scale

Acids• Compounds that forms H+ ions

in solution.• pH values below 7.• Acids taste sour • The lower the pH number the

stronger the acid.• Ex. Stomach acid, Vinegar,

Lemon juice.

Bases• Compounds that produces

hydroxide ions (OH-) in solution.

• Also known as alkaline solutions

• pH values above 7.• Bases taste bitter • The higher the pH the

stronger the base.• Ex. Ammonia, soap, bile.

pH scale• Used to indicate the concentration of H+ ions in a

solution.• Ranges from 0 to 14. • At a pH of 7, the concentration of H+ ions and OH-

ions are equal. • Pure water has a pH of 7.• Each step on the pH scale represents a factor of 10.

The following slides have MANY different looking pH scales

• They all say the same thing, just be used to seeing a variety for the class assessments

pH Scale