Biology Chapter 3: Water and Life

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Questions and Answers

What characteristic of water allows ice to float on its surface?

Ice is made of a less dense material than water.

Ice has a higher molecular weight than liquid water.

Ice is formed under higher pressure than liquid water.

Water is less dense as a solid than as a liquid. (correct)

What happens to water molecules as water cools down?

They begin to form more hydrogen bonds. (correct)

Hydrogen bonds break more frequently.

They become ionically bonded to each other.

They move faster due to lower energy.

Why is floating ice significant for aquatic life?

It allows ponds, lakes, and oceans to completely freeze.

It traps warm water in a layer below the ice.

It insulates the liquid water below, providing a habitat. (correct)

It prevents water from evaporating.

Which of the following accurately defines a solvent in a solution?

The dissolving agent of a solution. Signup and view all the answers

What interaction occurs when table salt (NaCl) is mixed with water?

Spheres of hydration form around the ions. Signup and view all the answers

What is the molarity of a solution if 2 moles of sodium chloride are dissolved in 1 liter of water?

2 M Signup and view all the answers

What is the molecular mass of sodium chloride (NaCl) based on its components?

58 Signup and view all the answers

Which of the following describes a characteristic of nonpolar molecules in relation to water?

They do not dissolve in water. Signup and view all the answers

What role does water play for hydrophilic substances?

It serves as a solvent. Signup and view all the answers

How is molarity defined in scientific terms?

Moles of solute per liter of solution. Signup and view all the answers

What is the pH of pure water?

7 Signup and view all the answers

Which substance is classified as a base?

NaOH Signup and view all the answers

How does an acid generally affect the concentration of OH- in a solution?

Decreases it Signup and view all the answers

What is the effect of buffers in biological fluids?

Minimize changes in pH Signup and view all the answers

What is the formula for calculating pH based on hydrogen ion concentration?

pH = -log [H+] Signup and view all the answers

Urine has a higher concentration of H+ compared to water. What is this relationship?

Urine is 10 times more acidic than water. Signup and view all the answers

Which component of the buffer system can donate hydrogen ions to lower pH?

Carbonic acid Signup and view all the answers

Which statement is true regarding the dissociation of water?

H+ concentration in water is 10-7 M. Signup and view all the answers

What property of water allows it to moderate temperature effectively?

High specific heat Signup and view all the answers

Which of the following best explains why water is known as a versatile solvent?

It can dissolve a wide range of substances due to its polarity. Signup and view all the answers

What is the phenomenon called where water molecules cling to the walls of a plant's vessels?

Adhesion Signup and view all the answers

How does water’s expansion upon freezing impact aquatic life?

It insulates the liquid water below, enabling life to exist even in frozen conditions. Signup and view all the answers

What is responsible for the high surface tension of water?

Hydrogen bonds Signup and view all the answers

What does a pH value of 7 indicate about a solution?

The solution is neutral. Signup and view all the answers

Why is evaporative cooling an important property of water?

It helps regulate temperature in living organisms. Signup and view all the answers

What type of bond forms between the oxygen atom of one water molecule and a hydrogen atom of another?

Hydrogen bond Signup and view all the answers

In the context of buffers, what role do they play in biological systems?

They resist changes in pH upon the addition of acids or bases. Signup and view all the answers

What defines the concept of molarity?

The concentration of solute in relation to volume of solvent. Signup and view all the answers

Study Notes

Water's Unique Properties

Water covers approximately three-quarters of Earth's surface, predominantly in liquid form.
It’s the only common substance that exists as a solid (ice), liquid, and gas (water vapor).

Molecular Structure and Bonds

A water molecule consists of one oxygen atom and two hydrogen atoms, linked by polar covalent bonds.
Oxygen's higher electronegativity leads to partial charges within the molecule, creating a polar structure.
Hydrogen bonds form between partially positive hydrogen atoms and the partially negative oxygen atoms in adjacent water molecules.

Emergent Properties of Water

Cohesive Behavior: Water’s high cohesion facilitates upward water movement in plants against gravity via hydrogen bonds.
Temperature Moderation: Water's high specific heat (1 calorie/(g·°C)) allows it to absorb and release significant amounts of heat, regulating temperature changes in the environment.
Expansion Upon Freezing: Ice is less dense than liquid water, allowing it to float. This phenomenon is essential for aquatic life, providing insulation for organisms beneath the ice layer.
Solvent Versatility: Water's polarity enables it to dissolve ionic and nonionic polar substances, making it an effective solvent.

Solutions and Molarity

A solution is a homogeneous mixture; the solvent dissolves the solute.
Molarity (M) represents the concentration of a solution in moles of solute per liter of solution; for example, a 1 M NaCl solution contains 1 mole of sodium chloride in 1 liter of water.
One mole equals Avogadro's number (6.02 x 10²³) of molecules, while molecular mass is the sum of the atomic masses of a molecule's components.

pH Scale and Acidity

The pH scale measures the acidity or basicity of a solution, with water being neutral at pH 7.
Acids increase H+ concentration, while bases increase OH- concentration in a solution. For example, HCl dissociates to increase H+, while NaOH increases OH-.
A tenfold change in H+ concentration represents a change of one pH unit (e.g., urine has a pH of 6, making it ten times more acidic than water).

Buffers

Buffers maintain stable pH levels in biological systems, typically between 6 and 8.
They can absorb excess H+ ions or donate them when needed, helping to minimize changes in acidity or basicity.
Carbonic acid in blood serves as a biological buffer, reacting with water to form bicarbonate and hydrogen ions to regulate pH levels effectively.

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Description

This quiz focuses on the essential role of water in biological systems as explored in Chapter 3. You will learn about water's properties, its significance for life, and the concepts of polarity, hydrogen bonds, molarity, and the pH scale. Mastering these concepts will enhance your understanding of chemistry and biology.