Properties of water and PH Scale

What are the properties of water?

Cohesive Behavior, Ability to Moderate Temperature, Expansion upon Freezing, Versatility of a Solvent, and Dissociation of Water molecules

What is the importance of water?

Supports all life, cells are about 70-95% water, waters properties and importance are due to its polar and and ability to form Hydrogen bonds

Polarity of Water

One side of a water molecule is slightly negative and the other side is slightly positive.

Oxygen

Negative dipole

Hydrogen

Positive dipole

Cohesion

Water sticking to itself

Adhesion

Water sticking to something else. Needs to be polar (nonmetal and nonmetal) or ionic (nonmetal and metal)

Hydrogen Bonds

Make up water, and are the reason why water has a high specific heat

Specific Heat

Waters resistance to heating or cooling

Capillary Action

Ability of water to move upwards against gravity (caused by cohesion and adhesion)

Example of Capillary Action

Water flowing up roots in a tree, paper towel soaking up liquid, water climbing up straw, etc.

Surface Tension

Inability to break surface of a liquid (An molecular film that covers water, resisting external forces and minimizing surface area)

Example of Surface Tension and Adhesion

Jesus strider walking on water

How does water moderate temperature?

Absorbing/releasing heat/energy into air

Heat

Form of energy (Common units: Celsius, Farenheit, Joules, etc.)

Temperature

Average kinetic energy of molecules (how warm/hot)

Why is waters specific heat so high?

Because of the hydrogen bonds. More energy is used to break these hydrogen bonds.

Examples of how specific heat affects life

1) Aquatic organisms can survive outside temperature changes because water heats + cools slowly

2) Organisms such as humans who are made mostly of water can survive temperature changes

Heat of evaporation

Amount of energy it takes to change something from a liquid to gas. Water has a high heat of vaporization

Why is the heat of vaporization so high for water?

To evaporate water, it needs to break the Hydrogen Bonds which takes a lot of energy. They're easy to break, but there are so many.

Examples of evaporative cooling

• Dog panting

• Human sweating

Freezing point of water

0 Celsius

What happens at 0 degrees?

Each water molecule becomes hydrogen bonded to four others creating a crystal lattice.

Which is less dense, ice or water?

Ice because of water expansion

Importance of expansion upon freezing

Aquatic organisms can survive winter temperatures.

Solution

A homogenous mixture. Homogenous meaning a mixture that looks the same throughout. All the parts are evenly mixed, and you can't see the different substances.

Solvent

Liquid doing the dissolving

Example of solvent

Water (Universal Solvent)

Solute

Solid being dissolved

Aqeous Solution

A solution in which water is the solvent

Why is water a good solvent?

It is polar. The negative dipole of oxygen is attracted to the positive dipole. It can separate substances, allowing them to dissolve easily.

Hydrophilic Substance

Things that are dissolved by water easily. (Water-loving, polar or ionic substance)

Example of Hydrophilic Substance

Salt, sugar

Hydrophobic Substance

Things that are not dissolved by water. (water-hating). Non-polar

Examples of Hydrophobic Substance

Oils, waxes

Why do most chemical reactions occur in water?

Molecules tend to bump into each other and react with one another. Water helps keep the dissolved substances spread out so these collisions can happen more easily.

3 ions

Hydrogen Plus (proton)

OH-

Hydroxide

What happens when you separate molecule?

It forms of a hydrogen plus (proton) and hydroxide ion

Hydroxide and Hydrogen cause what:

Water pH

What is pH determined by?

Hydrogen ions (Hydrogen plus, proton)

Acid

Proton donor (donates hydrogen plus ions)

Acids have:

Higher hydrogen plus (protons) concentrations then OH- (hydroxide concentrations)

Base

Proton acceptor

Base have:

Higher OH- (hydroxide) concentrations than Hydrogen plus (proton) concentrations

What pH range is acid?

Less than 7

What is neutral?

7 pH

When you go to the right on the pH scale, what happens?

Protons (hydrogen plus) goes down, OH- (hydroxide goes up)

When you go to the left on the pH scale, what happens?

Protons (hydrogen plus) go up, OH- (hydroxide goes down)

A change of one on the pH scale is how many times a change in H+ and OH- concentrations?

10 times

Heat of fusion

Amount of energy to change a solid to a liquid