Biology Chapter 3: Water and Life Quiz

Questions and Answers

What are the components of a water molecule?

Oxygen (O) is in the center and hydrogen (H) is on either side.

What is a polar molecule and why is water considered polar?

A polar molecule has an unequal distribution of charges. Water is considered polar because oxygen is more electronegative than hydrogen, attracting electrons more strongly.

How are the charged regions of each water molecule represented?

The oxygen region has a partial negative charge (-) and each hydrogen has a partial positive charge (+).

Explain hydrogen bonding and how many bonds can one water molecule form.

Hydrogen bonding occurs when the slightly positive hydrogen of one molecule is attracted to the slightly negative oxygen of another. A water molecule can form 4 hydrogen bonds. Signup and view all the answers

What is the difference between cohesion and adhesion?

Cohesion is the attraction between water molecules, while adhesion is the attraction between water molecules and other substances. Signup and view all the answers

What is demonstrated when you see beads of water on a waxed car hood?

Adhesion. Signup and view all the answers

Which property allows a water strider to walk on water?

Water's high surface tension. Signup and view all the answers

Define calorie in relation to water.

A calorie is the amount of heat needed to raise the temperature of 1g of water by 1ºC. Signup and view all the answers

What does it mean that water has high specific heat?

It means a large amount of heat must be absorbed or lost for 1g of water to change its temperature by 1°C. Signup and view all the answers

How does hydrogen bonding contribute to water's high specific heat?

Heat is used to break hydrogen bonds before the temperature of water can increase significantly. Signup and view all the answers

How does water’s high specific heat help moderate temperature?

It allows bodies of water to absorb and store heat, moderating temperatures in surrounding areas. Signup and view all the answers

What is evaporation?

Evaporation is the transformation of a liquid into a gas. Signup and view all the answers

What is the heat of vaporization?

It is the quantity of heat a liquid must absorb for 1g to be converted from liquid to gas. Signup and view all the answers

Why is the fact that ice floats important for aquatic life?

If ice sank, bodies of water would freeze solid, making life beneath the surface impossible. Signup and view all the answers

Why does ice float on water?

Ice is less dense than liquid water due to the arrangement of hydrogen bonds. Signup and view all the answers

What is the definition of solvent?

A solvent is the dissolving agent of a solution. Signup and view all the answers

What is a solution?

A liquid that is a completely homogeneous mixture of two or more substances. Signup and view all the answers

What is a solute?

A solute is the substance dissolved by the solvent. Signup and view all the answers

In a mixture of coffee and sugar, which is the solvent and which is the solute?

Coffee is the solvent and sugar is the solute. Signup and view all the answers

Why is water such a fine solvent?

Water's polarity allows it to dissolve ionic compounds and many polar molecules. Signup and view all the answers

Distinguish between hydrophobic and hydrophilic substances.

Hydrophilic substances have an affinity for water; hydrophobic substances repel water. Signup and view all the answers

Why do olive oil and water not mix?

Oil molecules are hydrophobic and cannot form hydrogen bonds with water. Signup and view all the answers

The molecular formula of sucrose is __________.

C12H22O11 Signup and view all the answers

How do you prepare a 1-molar solution of sucrose?

Add 342 g of sucrose to water to make it 1 liter. Signup and view all the answers

Can you prepare 1 liter of a 0.5-molar glucose solution?

Yes, add 90 g of glucose to water to bring it to a volume of 1 liter. Signup and view all the answers

Define molarity.

Molarity is the number of moles of solute per liter of solution. Signup and view all the answers

What two ions form when water dissociates?

Hydronium (H3O+) and hydroxide ions (OH-). Signup and view all the answers

What is the concentration of each ion in pure water at 25°C?

10^-7 M. Signup and view all the answers

Why does water have a pH of 7?

Water has equal concentrations of H+ and OH- ions, resulting in a neutral pH. Signup and view all the answers

What is the product of H+ and OH- concentrations in pure water?

10^-14. Signup and view all the answers

Define acid.

An acid is a substance that increases the hydrogen ion concentration of a solution. Signup and view all the answers

Define base.

A base is a substance that reduces the hydrogen ion concentration of a solution. Signup and view all the answers

How many times more acidic is a pH of 3 compared to a pH of 5?

100 times more acidic. Signup and view all the answers

How many times more basic is a pH of 12 compared to a pH of 8?

10,000 times more basic. Signup and view all the answers

What is the difference in H+ concentration between a pH of 8 and a pH of 12?

The H+ concentration of a pH 12 is 10,000 times lower than that of a pH of 8. Signup and view all the answers

Label the pH scale from 1 to 14.

Neutral is at pH 7, acidity increases from 7 to 0, and basicity increases from 7 to 14. Signup and view all the answers

How do buffers moderate pH changes?

Buffers minimize changes in H+ and OH- concentrations by accepting or donating hydrogen ions. Signup and view all the answers

What buffering system is present in the blood?

Carbonic acid and bicarbonate act as pH regulators in the blood. Signup and view all the answers

What are the sources of acid precipitation?

Burning fossil fuels releases CO2 and other oxides that react with water, altering pH. Signup and view all the answers

How do CO2 emissions impact marine life?

CO2 leads to ocean acidification, affecting calcification in marine organisms. Signup and view all the answers

Study Notes

Water Molecules and Polarity

Water molecules consist of an oxygen atom (O) in the center and two hydrogen atoms (H) on either side, forming a bent shape.
Water is a polar molecule due to the unequal sharing of electrons, with oxygen being more electronegative, resulting in partial negative (δ-) and partial positive (δ+) charges.

Hydrogen Bonding

Hydrogen bonds form between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another, allowing water molecules to hold together.
One water molecule can form up to four hydrogen bonds, contributing to water's unique properties.

Cohesion vs. Adhesion

Cohesion refers to the attraction among water molecules due to hydrogen bonding, while adhesion is the attraction between water and other substances.
The beading of water on a waxed car hood demonstrates adhesion, as water molecules cling to each other to form droplets.

Surface Tension

Water's high surface tension enables insects like water striders to walk on water due to the ordered arrangement of molecules at the surface.

Caloric Properties

A calorie is the amount of heat required to raise 1g of water by 1ºC and vice versa, equivalent to 4.184 Joules.
Water has a high specific heat (1 cal/g °C), meaning it can absorb significant amounts of heat with minimal temperature changes.

Temperature Regulation

Water's high specific heat aids in moderating environmental temperatures, preventing drastic temperature fluctuations in coastal areas and supporting life.

Evaporation and Heat of Vaporization

Evaporation is the process where liquid turns into gas, helping organisms regulate temperatures (e.g., cooling through sweat).
The heat of vaporization is the energy necessary for liquid water to become gas, influencing the severity of steam burns.

Ice Properties

Ice floats because it is less dense than liquid water, a result of its hydrogen bonding structure.
This floating behavior insulates bodies of water, preventing them from freezing solid and allowing life to thrive beneath the surface.

Solutions and Solubility

Water is known as a solvent, capable of dissolving various solutes due to its polarity.
Hydrophilic substances attract water and are soluble, while hydrophobic substances repel water and do not dissolve (e.g., oil).

Molarity and Ion Concentration

Molarity is the concentration of solute in a solution, expressed as moles of solute per liter of solution.
Water dissociates into hydronium (H3O+) and hydroxide ions (OH-), with a neutral pH of 7 indicating equal concentrations of both ions (10^-7 M).

pH Scale and Buffers

The pH scale reflects the concentration of hydrogen ions, with each unit change representing a tenfold change in acidity or basicity.
Buffers maintain stable pH in solutions by absorbing or releasing H+ ions, essential for biological systems.

Carbon Dioxide and Blood pH Regulation

Carbonic acid forms from the reaction of CO2 and water, dissociating to help regulate blood pH through equilibrium with bicarbonate and hydrogen ions.

Acid Precipitation and CO2 Effects

Human activities, particularly the burning of fossil fuels, contribute to acid precipitation, altering the pH and temperature of water bodies.
Increased CO2 levels lead to ocean acidification, harming marine life due to decreased carbonate concentrations essential for shell formation.

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Test your knowledge on the essential properties of water and its role in life processes with this flashcard quiz. Explore molecular structure, polarity, and the significance of water in biological systems.