Biology Chapter 3: The Role of Water
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Questions and Answers

What charge does the oxygen atom in a water molecule carry?

  • Partial negative charge (correct)
  • Positive charge
  • Partial positive charge
  • Neutral charge

Which physical states can water exist in simultaneously in the natural environment?

  • Solid, liquid, and gas (correct)
  • Solid and liquid only
  • Liquid and gas only
  • Gas and solid only

Which property of water is mainly responsible for the movement of water in plants?

  • Versatility as a solvent
  • Cohesive behavior (correct)
  • Temperature moderation
  • Expansion upon freezing

How strong are hydrogen bonds in liquid water compared to covalent bonds?

<p>About one-twentieth as strong as covalent bonds (D)</p> Signup and view all the answers

What happens to water when it freezes?

<p>It expands and becomes less dense (D)</p> Signup and view all the answers

What is the role of hydrogen bonds in water?

<p>They hold water molecules together, allowing for properties like cohesion (D)</p> Signup and view all the answers

Why is water referred to as a versatile solvent?

<p>It can dissolve a wide range of substances due to its polarity (C)</p> Signup and view all the answers

Which of the following statements about the structure of water is true?

<p>It has a V-shaped structure with polar covalent bonds (D)</p> Signup and view all the answers

What role does adhesion play in the movement of water in plants?

<p>It helps water molecules cling to the walls of the vessels. (D)</p> Signup and view all the answers

How does water's high surface tension affect certain animals?

<p>It enables them to walk on the surface without breaking it. (D)</p> Signup and view all the answers

Which statement best describes the relationship between heat and temperature?

<p>Heat measures total kinetic energy while temperature measures average kinetic energy. (A)</p> Signup and view all the answers

What is the definition of heat in the context of matter?

<p>The total quantity of thermal energy within a substance. (A)</p> Signup and view all the answers

At what temperature does water boil at sea level in degrees Celsius?

<p>100°C (D)</p> Signup and view all the answers

What is the primary consequence of water's high specific heat?

<p>It moderates temperature changes in the environment. (A)</p> Signup and view all the answers

Which best defines a calorie in the context of heat energy?

<p>The heat required to raise the temperature of 1 g of water by 1°C. (D)</p> Signup and view all the answers

Which characteristic of water contributes to its ability to absorb and release large amounts of heat?

<p>The presence of hydrogen bonds. (D)</p> Signup and view all the answers

What happens to the temperature of an ice cube when it absorbs heat from a warmer object?

<p>The temperature of the ice cube increases while cooling the other object. (C)</p> Signup and view all the answers

What is the equivalent of one joule in terms of calories?

<p>0.239 cal (C)</p> Signup and view all the answers

What is the primary reason water has a high heat of vaporization?

<p>Hydrogen bonds must be broken (B)</p> Signup and view all the answers

What is the phenomenon that explains why evaporating liquids cool their remaining surface?

<p>Evaporative cooling (C)</p> Signup and view all the answers

Why do oceans and lakes not freeze solid in winter?

<p>Ice layers insulate the water below (B)</p> Signup and view all the answers

At what temperature does water begin to freeze and form a crystalline network?

<p>0°C (D)</p> Signup and view all the answers

What characteristic of water allows it to dissolve many substances effectively?

<p>The polarity of water molecules (A)</p> Signup and view all the answers

Which of the following statements best describes why ice floats on water?

<p>Ice is less dense than water at 4°C (C)</p> Signup and view all the answers

What defines a liquid that is a completely homogeneous mixture of two or more substances?

<p>A solution (B)</p> Signup and view all the answers

Why is water not considered a universal solvent?

<p>Not all substances can dissolve in it (D)</p> Signup and view all the answers

What happens to water molecules as they begin to freeze?

<p>They form a crystalline structure (D)</p> Signup and view all the answers

What impact does evaporative cooling have on temperature regulation in organisms?

<p>It helps maintain optimal temperatures for biochemical processes (D)</p> Signup and view all the answers

What effect does adding hydrochloric acid to water have on the hydrogen ion concentration?

<p>It increases the hydrogen ion concentration. (A)</p> Signup and view all the answers

Which statement correctly describes the pH of a neutral solution at 25°C?

<p>pH is equal to 7. (B)</p> Signup and view all the answers

How do bases typically reduce hydrogen ion concentration in a solution?

<p>By either accepting hydrogen ions or producing hydroxide ions. (D)</p> Signup and view all the answers

What is indicated by the double arrows in the reaction involving ammonia?

<p>The reaction can shift in both directions. (A)</p> Signup and view all the answers

Which of the following ions is produced when sodium hydroxide dissociates in water?

<p>OH- (B)</p> Signup and view all the answers

What relationship can be inferred from the equation [H+][OH-]=10^{-14} at 25°C?

<p>Increasing one concentration decreases the other. (C)</p> Signup and view all the answers

Which of the following statements correctly describes a strong acid?

<p>It completely dissociates and increases H+ concentration. (C)</p> Signup and view all the answers

What is the weight in grams of one mole of sucrose?

<p>342 g (D)</p> Signup and view all the answers

If substance A has a molecular weight of 10 daltons, how many grams of substance A contain the same number of molecules as 100 grams of substance B with a molecular weight of 100 daltons?

<p>10 g (A)</p> Signup and view all the answers

How is a one-molar (1 M) solution defined?

<p>1 mole of solute in 1 liter of solvent (C)</p> Signup and view all the answers

What happens to a water molecule during the dissociation process?

<p>It becomes a hydronium ion. (D)</p> Signup and view all the answers

What is the equilibrium concentration of H+ or OH- ions in pure water at 25°C?

<p>$10^{-7}M$ (B)</p> Signup and view all the answers

Which of the following best describes molarity?

<p>Number of moles per liter of solution (D)</p> Signup and view all the answers

The reaction of water dissociation is characterized by what type of process?

<p>Reversible process (C)</p> Signup and view all the answers

What is the role of the hydrogen ion (H+) after it dissociates from a water molecule?

<p>It acts as a proton donor. (A)</p> Signup and view all the answers

Which substance would contain more molecules in 1 gram, sucrose or ethyl alcohol (C2H6O)?

<p>Ethyl alcohol contains more molecules. (D)</p> Signup and view all the answers

The advantage of using a mole as a unit of measure is that it allows for what?

<p>Understanding of molecular behavior (C)</p> Signup and view all the answers

Flashcards

Hydrogen bonds in water

Attractive forces between water molecules, causing water to be cohesive.

Cohesion in water

Water molecules sticking together due to hydrogen bonds.

Adhesion in water

Water molecules sticking to other surfaces.

Surface tension of water

Force needed to stretch or break the water's surface. High due to hydrogen bonds.

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Water's high specific heat

Water absorbs or releases significant heat with little temperature change.

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Heat

Total kinetic energy of molecules in a substance.

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Temperature

Average kinetic energy of molecules; a measure of heat intensity.

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Calorie

Heat energy required to raise the temperature of 1 gram of water by 1°C.

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Water's role in temperature moderation

Water absorbs or releases heat, maintaining relatively stable temperatures in its surroundings.

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Water freezing/boiling point

Water freezes at 0°C and boils at 100°C at sea level.

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Heat of Vaporization of Water

The amount of heat needed to change a unit of water from liquid to gas.

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Evaporative Cooling

Cooling of a surface as the liquid evaporates, leaving cooler molecules behind.

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Water's Density Anomaly

Water is less dense as a solid (ice) than as a liquid, unlike most substances.

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Hydrogen Bonds in Water

Weak attractions between water molecules, crucial for water's unique properties.

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Water as a Solvent

Water dissolves many substances because it can form hydrogen bonds with them.

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Solution

A homogeneous mixture of two or more substances, where one substance (solute) is dissolved in another (solvent).

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Aqueous Solution

A solution in which water is the solvent.

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Ice Floating

Ice is less dense than liquid water, causing it to float.

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Water's Importance to Life

Water's unique properties, including its ability to dissolve substances and ability to float in its frozen form, create an essential environment for life.

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Polarity of Water

Water's uneven distribution of electrical charge, leading to its properties as a solvent and its ability to form hydrogen bonds.

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Mole of a substance

A unit of measurement representing 6.02 x 10^23 molecules of a substance, weighing the same as its molecular weight in grams.

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Molecular Weight (in daltons)

The sum of the weights of all atoms in a molecule

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Molarity

The concentration of a substance in a solution, measured as moles of solute per liter of solution.

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1 M solution

A solution containing 1 mole of solute per liter of solvent.

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Hydrogen ion (H+)

A proton released when a water molecule dissociates.

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Hydroxide ion (OH-)

A negatively charged ion formed when a water molecule loses a hydrogen.

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Hydronium ion (H3O+)

A water molecule with an extra proton.

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Water dissociation

The reversible process where water molecules split into hydrogen ions (H+) and hydroxide ions (OH-).

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Concentration of H+ and OH- in water

At equilibrium, the concentration of H+ and OH- in pure water is 10^-7 M (at 25°C).

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Importance of water dissociation

Changes in the concentrations of hydrogen and hydroxide ions significantly affect the chemistry of living organisms.

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Acid

A substance that increases the concentration of hydrogen ions (H+) in a solution, making it more acidic.

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Base

A substance, that reduces the hydrogen ion concentration in a solution, either by directly accepting H+ ions or indirectly increasing the concentration of hydroxide (OH-) ions, which combine with H+ to form water.

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pH scale

A logarithmic scale used to describe how acidic or basic a solution is, based on the concentration of hydrogen ions (H+).

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Strong Acid/Base

Substances that completely dissociate (break apart) into their ions when dissolved in water.

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Weak Acid/Base

Substances that only partially dissociate in water. The reaction between the acid/base and the water is reversible.

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Neutral Solution

A solution where the concentration of hydrogen ions (H+) is equal to the concentration of hydroxide ions (OH-).

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Equilibrium

A state in a reversible chemical reaction where the rate of the forward reaction equals the rate of the reverse reaction, resulting in no net change in the concentrations of the reactants and products.

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Water's Polarity

Water molecules have a slightly negative end (oxygen) and a slightly positive end (hydrogen), due to oxygen's higher electronegativity.

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Hydrogen Bonds

Weak attractions between the positive hydrogen of one water molecule and the negative oxygen of another water molecule.

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Cohesion in Water

Water molecules sticking together due to hydrogen bonds.

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Water's Role in Plant Transport

Cohesion helps water move upwards in plants.

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Water's High Specific Heat

Water can absorb or release large amounts of heat with relatively little temperature change.

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Water's Density Change on Freezing

Water expands when it freezes, making ice less dense than liquid water.

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Water as a Solvent

Water dissolves many substances due to its polarity, allowing life processes to occur.

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Water's Importance for Life

Water is essential for all life on Earth because of its unique properties, including polarity, hydrogen bonding, cohesion, and high specific heat.

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Study Notes

Overview: The Molecule That Supports All of Life

  • Water is essential for life on Earth
  • All organisms are composed primarily of water
  • Water exists in all three states of matter (solid, liquid, and gas)
  • Three-quarters of Earth's surface is covered by water
  • Terrestrial organisms are also reliant on water
  • Cells are 70-95% water
  • Water participates in many life processes

Concept 3.1: Polarity and Hydrogen Bonding

  • Water molecules have a bent, V-shaped structure
  • Water is a polar molecule due to oxygen's higher electronegativity
  • Oxygen has a partial negative charge (δ-)
  • Hydrogen atoms have a partial positive charge (δ+)
  • These partial charges allow water molecules to attract each other through hydrogen bonds
  • Hydrogen bonds are relatively weak compared to covalent bonds
  • Water molecules can form hydrogen bonds with up to four neighbors
  • Hydrogen bonds are constantly forming, breaking, and reforming in liquid water

Concept 3.2: Four Emergent Properties

  • Cohesion: Hydrogen bonding creates cohesion, causing water molecules to stick together
  • Cohesion in Plants: Water transport in plants (from roots to leaves) relies on cohesion
  • Adhesion: Attraction of water molecules to other substances (e.g., the sides of vessels in plants)
  • Surface Tension: Water's resistant to being stretched or broken at its surface due to cohesion
  • Water's Ability to Moderate Temperature: Water absorbs and releases large amounts of heat with little temperature change
  • Heat: A measure of the total amount of kinetic energy in a substance
  • Temperature: A measure of average kinetic energy
  • Specific Heat: The amount of heat required to raise the temperature of 1 gram of a substance by 1°C; water has a much higher specific heat than most substances, helping to moderate temperature fluctuations
  • Heat of Vaporization: The amount of heat needed to turn 1g of water into a gas; water's high heat of vaporization has many important ecological effects
  • Evaporative Cooling: The cooling effect that occurs when water evaporates (water molecules with higher kinetic energy escape)

Concept 3.3: Water's Role as a Solvent

  • Solution: A homogeneous mixture of substances

  • Solvent: The dissolving substance

  • Solute: The substance that dissolves

  • Water as a Solvent: Water is a versatile solvent because of its polarity, allowing it to dissolve many ionic and polar substances.

  • Hydrophilic: Substances that have an affinity for water (water-loving)

  • Hydrophobic: Substances that do not have an affinity for water (water-fearing)

  • pH: A scale that measures the concentration of hydrogen ions (H+) in a solution

  • Acids: Substances that increase H+ concentration (pH less than 7)

  • Bases: Substances that decrease H+ concentration (pH greater than 7)

  • Water's dissociation: H2O ⇌ H+ + OH- (water molecules dissociate into hydrogen and hydroxide ions)

  • Buffers: Substances that resist changes in pH

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Chapter 3: Water and Life Handout PDF

Description

Understand the vital role water plays in supporting life on Earth. This chapter explores the molecular structure of water, its polarity, and the significance of hydrogen bonding. Additionally, learn about the emergent properties of water that are crucial for various biological processes.

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