Chapter 3

Chemistry of Life

Content Objectives Write these down!

I will be able to identify:

• What makes water a unique substance.

• How the presence of various substances dissolved in water affect the properties of water.

Adapted from Holt Biology 2008

Chapter 3 Section 2: Water & Solutions

Key Vocabulary Terms

Adapted from Holt Biology 2008

Cohesion

The force that holds molecules of a single material together.

The attraction of particles of the same substance.

Adapted from Holt Biology 2008

Adhesion

The attractive force between two bodies of

different substances that are in contact with each

other.

Adapted from Holt Biology 2008

Solution

A homogeneous mixture throughout which two or

more substances are uniformly dispersed.

Adapted from Holt Biology 2008

Acid

Any compound that increases the number of hydronium ions when dissolved in water; acids turn blue litmus paper red and react with bases

and some metals to form salts.

Adapted from Holt Biology 2008

Base

Any compound that increases the number of hydroxide ions when dissolved in water; bases

turn red litmus paper blue and react with acids to form salts.

Adapted from Holt Biology 2008

pH

A value that is used to express the acidity or alkalinity (basicity) of a system; each whole

number on the scale indicates a tenfold change in acidity; a pH of 7 is neutral, a pH of less than 7 is

acidic, and a pH of greater than 7 is basic.

Adapted from Holt Biology 2008

Buffer

A solution made from a weak acid and its

conjugate base that neutralizes small amounts of acids or bases added to

it.

Adapted from Holt Biology 2008

Chapter 3 Section 2: Water & Solutions

Supplementary Words

Adapted from Holt Biology 2008

Hydronium Ions

The solution in which the solvent is water where an ion with fewer electrons

than protons forms, giving it a positive charge (

H3O+), Oxygen forms 3 bonds picking up an additional Hydrogen

proton.

Adapted from Holt Biology 2008

Hydroxide Ions

Hydroxide is a polyatomic ion consisting of oxygen

and hydrogen: OH− It has a charge of −1. Hydroxide is one of the simplest of

the polyatomic ions.

Adapted from Holt Biology 2008

Hydrochloric Acid HCl

Hydrochloric acid is a solution of hydrogen chloride (HCl) in water, that is a highly corrosive, strong mineral acid with many industrial uses. It

is found naturally in gastric acid.

Adapted from Holt Biology 2008

Sodium Hydroxide NaOH

Sodium hydroxide (NaOH), also known as lye

and caustic soda, is a caustic metallic base.

Adapted from Holt Biology 2008

Chapter 3 Section 2:

Water & Solutions

Notes

Section 2: Water and Solutions

Properties of Water

Solutions

Properties of Water

Unique properties make water an important substance for life.

Properties of Water

Unique properties result from hydrogen bonds.

Properties of Water

When water freezes, the crystal structure formed due to

hydrogen bonding makes ice less dense than liquid water.

Properties of Water, continued

Water can absorb a large amount of heat without changing temperature. This property can help organisms maintain a

constant internal temperature.

Properties of Water, continued

The attraction of particles of the same substance, such as water, is called

cohesion. Cohesion keeps water from evaporating easily; thus, water is a

liquid at ordinary temperatures.

Properties of Water, continued

Water molecules also stick to other polar molecules. This attraction between particles of different substances is called adhesion.

Think, Share, Write #1

What are some unique properties of water?

Think, Share, Write #1 • What are some unique properties of water?

1. Cohesion 2. Surface Tension 3. Adhesion 4. Imbibition: The

process of soaking into a hydrophilic substance. Water being taken into a sponge, into a seed, into paper towels.

5. High Specific Heat

6. High Heat of Vaporization

7. Freezing and Expansion of Water

8. Versatile Solvent

Solutions

A solution is a mixture in which ions or molecules of one or more

substances are evenly distributed in another substance.

solvent

A solvent is the substance that dissolves the solute to make a solution.

solute

A solute is a substance that dissolves in a solution.

Solutions

Many substances are transported throughout living things as solutions of water. Dissolved substances can

move more easily within and between cells.

Solutions

Water dissolves many ionic and polar substances but does not dissolve

nonpolar substances.

Adapted from Holt Biology 2008

YOUR TURN

With a partner, read the Chapter 3 Section 2 Active Reading – Water and Solutions

1st - Take turns reading the questions aloud to each other, alternating questions.

2nd - Take turns reading the selection aloud to each other, alternating sentences or paragraphs.

Adapted from Holt Biology 2008 Adapted from Holt Biology 2008

YOUR TURN

As you read discuss the content.

Reread and discuss each question. Write down the best answer to the question using full descriptive sentences.

• Be prepared to share with the class.

Adapted from Holt Biology 2008

2

Solutions, continued

Some water molecules break apart to form hydronium and hydroxide

ions.

Acids and Bases

Solutions, continued

In pure water, hydronium and hydroxide ions are present in equal

numbers.

Acids and Bases

Solutions, continued

Acids and bases are compounds that change the balance of the hydronium

& hydroxide ions.

Acids and

Bases

Solutions, continued

Acids are compounds that form extra hydronium ions when dissolved in

water.

Acids and Bases

Solutions, continued

Bases are compounds that form extra hydroxide ions when dissolved in

water.

Acids and Bases

Solutions, continued

When acids and bases are mixed, the extra hydronium and hydroxide ions

react to form water.

Acids and Bases

Solutions, continued

pH (potential of Hydrogen) is a measure of how acidic or basic a

solution is.

pH and Buffers

Solutions, continued

Each one-point increase in pH represents a 10-fold decrease in

hydronium ion concentration.

pH and Buffers

Solutions, continued

Pure water has a pH of 7

Acidic solutions have a pH below 7

Basic solutions have a pH above 7

pH and Buffers

Solutions, continued

The pH of solutions in living things must be stable.

pH and Buffers

Solutions, continued

For a stable pH to be maintained, the solutions in living things

contain buffers.

pH and Buffers

Solutions, continued

A buffer is a substance that reacts to prevent pH changes in a

solution.

pH and Buffers

Think, Share, Write #2

What is pH?

Think, Share, Write #2

What is pH?

pH is a measure of how acidic or basic a solution