Chapter 3: Water and Life

Questions in chapter 3 biology is added from the Pearson questions or book.

The partial charges on a water molecule occur because of __________.

Answer: the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule.

A mole of methanol (CH₃OH) weighs 32 g. The number of grams of methanol that are needed to produce 1 L of a 1 millimolar solution is __________.

Answer: 0.032 g


Explanation: In order to solve this problem, convert 1 millimolar to molar units. A millimolar unit is a unit of 1/1,000 molar units. Since we have 1/1,000 molar units, this gives us the decimal 0.001. To calculate the amount of grams needed for this solution, multiply 46 g × 0.001 = 0.032 g.

Adhesion is best described as __________.

Answer: the clinging of one substance to another substance.

Explanation: Adhesion is the attraction of one substance to another. Water transport in plants is aided by the adhesion of the water to cell walls by hydrogen bonds. This helps resist the downward pull of gravity. This is the correct answer.

Water is a polar molecule. This means that __________.

Anwser: the opposite ends of the molecule have opposite electrical charges.

Water moves up a plant because of hydrogen bonds by a process called __________.

Anwser: cohesion and adhesion.

A compound that donates hydrogen ions to a solution is __________.

Answer: an acid.

Explanation: When acids dissolve in water, they donate additional H⁺ to the solution. An acid is a substance that increases the hydrogen ion concentration of a solution. For example, when hydrochloric acid (HCl) is added to water, hydrogen ions dissociate from chloride ions: HCl → H⁺ + Cl–. This source of H⁺ (dissociation of water is the other source) results in an acidic solution—one having more H⁺ than OH^–.

A solution at pH 10 contains __________ than the same amount of solution at pH 8.

Answer: 100 times less H⁺

Explanation: The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration: pH log [H⁺]. For a neutral aqueous solution, [H⁺] is 10–7 M, giving us log 10–7 = –(–7) = 7. Notice that pH declines as H⁺ concentration increases. Remember that each pH unit represents a tenfold difference in H⁺ and OH^–concentrations. It is this mathematical feature that makes the pH scale so compact. A solution of pH 3 is not twice as acidic as a solution of pH 6, but a thousand times (10 × 10 × 10) more acidic. When the pH of a solution changes slightly, the actual concentrations of H⁺ and OH^– in the solution change substantially. Since the difference between pH 10 and pH 8 is “10 × 10,” this pH 10 solution is 100 times more alkaline than the pH 8 solution.

The amount of heat required to change the temperature of 1 g of any substance by one °C is defined as __________.

Answer: the specific heat of that substance.

Explanation: The amount of heat required to change the temperature of 1 g of any substance by one °C is defined as the specific heat of that substance.

The absorption of human-generated CO₂ by the oceans __________.

Anwser: All of the listed responses are correct.

Explanation: The absorption of human-generated CO₂ by the oceans increases the oceanic concentration of carbonic acid because it reacts with water to form carbonic acid, it increases the oceans' acidity and lowers the pH of seawater, reduces the carbonate ion concentration in the oceans and threatens calcifying organisms in marine ecosystems because the absorption of CO₂ by the oceans leads to a decrease in the carbonate ion concentration, which is required for calcification, the production of calcium carbonate (CaCO₃) by many marine organisms, and increases the hydrogen ion concentration in the oceans but decreases the carbonate ion concentration and threatens the livability of the oceans for calcifying organisms. The absorption of CO₂ by the oceans causes an increase in the carbonic acid, and hydrogen ion concentration (lower pH). The extra hydrogen ions bind with the carbonate ion to form bicarbonate. This reduces the amount of carbonate ions available for calcification, the production of calcium carbonate (CaCO₃) by many marine organisms, including reef-building corals and animals that build shells. The absorption of CO₂ by the oceans causes an increase in the carbonic acid, and hydrogen ion concentration (lower pH). The extra hydrogen ions bind with the carbonate ion to form bicarbonate. This reduces the amount of carbonate ions available for calcification, the production of calcium carbonate (CaCO₃) by many marine organisms, including reef-building corals and animals that build shells

Urine, at pH 6, contains __________ H⁺ as household bleach, at pH 13.

Answer: Urine, at pH 6, contains 10,000,000 times as much H⁺ as household bleach, at pH 13.

Explanation: The pH scale compresses the range of H⁺ and OH^– concentrations by employing logarithms. The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration: pH log [H⁺]. For a neutral aqueous solution, [H⁺] is 10–7 M, giving us log 10–7 = –(–7) = 7. Notice that pH declines as H⁺ concentration increases. Remember that each pH unit represents a tenfold difference in H⁺ and OH^– concentrations. It is this mathematical feature that makes the pH scale so compact. A solution of pH 3 is not twice as acidic as a solution of pH 6, but a thousand times (10 × 10 × 10) more acidic. When the pH of a solution changes slightly, the actual concentrations of H⁺ and OH^– in the solution change substantially. Since the difference between pH 6 and pH 13 is “107,” urine is 10,000,000 times more acidic than household bleach.

When the pH of a solution shifts from 3 to 7, the hydrogen ion concentration has changed, and __________.

Answer: it has decreased by 10,000 times.

Explanation: The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration: pH log [H⁺]. For a neutral aqueous solution, [H⁺] is 10^–7 M, giving us log 10^–7 = –(–7) = 7. Notice that pH declines as H⁺ concentration increases. Remember that each pH unit represents a tenfold difference in H⁺ and OH^– concentrations. It is this mathematical feature that makes the pH scale so compact. A solution of pH 3 is not twice as acidic as a solution of pH 6, but a thousand times (10 × 10 × 10) more acidic. Because the pH number is the negative log of the hydrogen ion concentration, a change from a pH of 7 to a pH of 3 increases the hydrogen ion concentration by 10,000 times (7 – 3 = 4; [10 × 10 × 10 × 10] 10⁴ = 10,000).

Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability of sweat to lower body temperature?

Explanation: The absorption of heat by the breaking of hydrogen bonds. What You Need.

A substance that reduces the hydrogen ion concentration of a solution is __________.

Answer: a base.

Explanation: When bases dissolve in water, they donate additional OH⁺ to the solution, thereby increasing the hydroxyl ion concentration of a solution. For example, when sodium (NaOH) is added to water, hydroxyl ions dissociate from sodium ions: NaOH  Na⁺ + OH^– . This source of OH^– (dissociation of water is the other source) results in an alkaline or basic solution—one having more OH^– than H⁺.

Glucose has a molecular mass of 180 daltons. To make a 2-molar (2 M) solution of glucose, __________.

Answer: Stir 360 g of glucose in water to dissolve the sugar, and then add enough water to bring the total volume of the solution up to 1 L

Explnation: If we wanted to make a liter (L) of solution consisting of 1 mol of glucose dissolved in water, we would measure out 180 g of glucose and then gradually add water, while stirring, until the sugar was completely dissolved. We would then add enough water to bring the total volume of the solution up to 1 L. At that point, we would have a 1-molar (1 M) solution of glucose. In this problem we want a 2 M solution. That means that we must double the amount of grams that we weigh out and measure out 360 g of glucose and then gradually bring the total volume of the solution up to 1 L.

 

__________ is an emergent property of water that allows insects like the raft spider to walk on water.

Anwser: Surface tension

Explnation: Surface tension is related to cohesion, a measure of how difficult it is to stretch or break the surface of a liquid. At the interface between water and air is an ordered arrangement of water molecules, hydrogen-bonded to one another and to the water below. This gives water an unusually high surface tension, making it behave as though it were coated with an invisible film. You can observe the surface tension of water by slightly overfilling a drinking glass; the water will stand above the rim. The spider pictured here takes advantage of the surface tension of water to walk across a pond without breaking the surface.

 

Electronegativity is

Answer: the attraction of an atom for the electrons in a covalent bond.

Explanation: Atoms in a molecule attract shared bonding electrons to varying degrees, depending on the element. The more electronegative an atom is, the more strongly it pulls shared electrons toward itself.

A polar covalent bond between two atoms results from

Answer: two atoms that do not have similar electronegativities.

Explanation: When an atom is bonded to a more electronegative atom, the electrons of the bond are not shared equally. This type of bond is called a polar covalent bond. Such bonds vary in their polarity, depending on the relative electronegativity of the two atoms.

Which of the following statements helps to explain why water molecules form hydrogen bonds?

Answer: Attractions form between opposite partial charges.


Explanation: Elements, not molecules, can be electronegative. When a hydrogen atom is covalently bonded to an electronegative atom such as oxygen in water, the hydrogen atom has a partial positive charge and the oxygen atom has a partial negative charge, making water a polar molecule. The hydrogen atom is attracted to a different electronegative atom nearby. This attraction between the partial positive charge on the hydrogen atom and the partial negative charge on an electronegative atom is called a hydrogen bond.

Cells are surrounded by water, with which they are mostly filled. Which of the following occurs as a result?

A variety of nutrient molecules is readily available as dissolved solutes.

Waste products produced by cell metabolism can be easily removed.

The temperature of living things tends to change relatively slowly.


Anwser: All of the listed responses are correct.

Explnation: All of the listed responses result from the extraordinary characteristics of water.

Water is a polar molecule. What does this statement mean?

Answer: That atoms in the molecule have partial charges as a result of unequal sharing of electrons in a covalent bond.

Explanation: In the case of water, the oxygen is slightly negative, and the hydrogen atoms are slightly positive.

The partial charges on a water molecule occur because of __________.

Answer: the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule.


Explanation: Because oxygen is more electronegative than hydrogen, electrons of the polar bond spend more time closer to the oxygen atom, resulting in a slight negative charge on the oxygen atom and slight positive charges on the hydrogen atoms.

In a group of water molecules, hydrogen bonds form between which of the following?

Answer: The oxygen atom in one water molecule and a hydrogen atom in another water molecule.

Explanation: The slightly negatively charged region of an oxygen atom of one water molecule is attracted to the slightly positively charged region of a hydrogen atom of another water molecule.

Which of the following accurately relates the emergent properties of water to the effects of global warming in the Arctic?

Answer: Ice floats because it is less dense than liquid water; floating ice insulates water below and provides a habitat for some species. The significant increase in Arctic air temperature over the past 50 years is causing a reduction in sea ice, compromising these beneficial effects of sea ice.

Explanation: The warming that has occurred in the Arctic has significantly affected the seasonal balance between ice and liquid water to the degree that sea ice communities are in danger.

If water were not a polar molecule, how would the effects of climatic warming differ from those currently observed or predicted to occur in the future?

Answer: The effects would be drastically worse because the loss of the polar nature of water would greatly reduce its specific heat and its ability to moderate temperature.

Explanation: A loss of the polar nature of water would equate to a loss in the ability to form hydrogen bonds. Breaking hydrogen bonds absorbs energy, which accounts for water's high specific heat and its ability to influence and moderate climate.

The tendency of water molecules to stay close to each other as a result of hydrogen bonding __________.

Anwser: is called cohesion, acts to moderate temperature, provides the surface tension that allows small animals to move across a water surface, and helps to keep water moving through the vessels in a tree trunk.

Explanation: All of the choices reflect results of the cohesiveness of water molecules.

What do cohesion, surface tension, and adhesion have in common with reference to water?

Anwser: All are properties related to hydrogen bonding.

Explanation: The extraordinary qualities of water are emergent properties resulting from hydrogen bonding.

The ability of water molecules to form hydrogen bonds with other water molecules and water's ability to dissolve substances that have charges or partial charges are __________.

Anwser: both caused by water's partial charges.

Explanation: Two molecules of water are held together by a hydrogen bond formed between the slight positive charge of the hydrogen and the slight negative charge of the oxygen. Water is a very versatile solvent, a quality traced to the polarity of the water molecule.

The phenomenon responsible for maintaining the upward movement of water through vessels in a tree is __________.

Answer: cohesion.

Explanation: Cohesion is a consequence of hydrogen bonding between water molecules.

Adhesion is best described as which of the following?

Answer: The clinging of one substance to another substance.

Explanation: Adhesion is the attraction of one substance to another.

You can fill a glass of water to just slightly above the rim without the water spilling over the glass. What property of water best explains this phenomenon?

Anwser: Surface tension.

Explanation: Water has a greater surface tension, a measure of how difficult it is to break the surface of a liquid, than most other liquids.

Which action would involve the greatest transfer of heat?

Anwser: Condensing 5 g of steam to liquid water.

Explanation: This would release about 2,900 calories (580 calories/gram × 5 grams).

Imagine that organisms consisted of 70–95% alcohol instead of 70–95% water. Alcohol's specific heat is about half that of water. How would living things be different?

Anwser:Systems for temperature regulation would have to be much more efficient.

Explanation: In order for living things to inhabit a wide range of environments, temperature regulation would need to be more efficient for a fluid with a lower specific heat.

The amount of heat required to change the temperature of 1 g of any substance by 1°C is defined as __________.

Anwser: the specific heat of that substance.

Explnation: The specific heat of a substance is defined as the amount of heat that must be absorbed or lost to change the temperature of 1 g of that substance by 1°C.

The amount of heat required to convert 1 g of any substance from the liquid to the gaseous state is defined as __________.

Anwser: the heat of vaporization of that substance.

Explanation: Heat of vaporization is the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state.

The reason that coastal climates are more moderate than inland climates primarily water's high __________.

Anwser: specific heat


Explanation: Because of its high specific heat, water's temperature will change less when it absorbs or loses a given amount of heat. Thus, the oceans can absorb and store a huge amount of heat and release it later when the temperature of the air has dropped.

Sweating has a cooling effect because of water's high __________.

Answer: heat of vaporization

Explanation: Water's high heat of vaporization results in evaporative cooling because when water evaporates, the surface on which it rests cools down.

Water has __________ than other liquids such as ethanol, reflecting its capacity to absorb large amounts of heat.

Answer: a higher boiling point.

Explanation: More heat is needed to vaporize 1 g of water than most other liquids.

Which of the following occurs because molecules of water are farther apart in ice than in liquid water?

Anwser: Ice floats.

Explnation: Because water molecules in ice are farther apart than in liquid water, ice is less dense, and therefore, it floats.

Water is a very versatile solvent because water molecules are __________.

Anwser: polar.

Explanation: Because molecules of polar solvents have a positive and a negative pole, polar solvents are excellent solvents for ions and for other polar materials.

How does the polarity of water contribute to its ability to dissolve so many substances?

Answer: Because it is polar, water's negatively charged oxygen atoms and positively charged hydrogen atoms are attracted to positively and negatively charged ions and molecules.

Explanation: Polar water molecules surround the individual ions or charged molecules, separating and shielding the ions or molecules from one another.

What are nonpolar molecules that cluster away from water molecules called?

Anwser: Hydrophobic

Explanation: Substances that are nonionic and nonpolar repel water.

A molecule that has all nonpolar covalent bonds would be __________.

Anwser: hydrophobic

Explanation: For example, the hydrophobic behavior of oil molecules results from a prevalence of nonpolar covalent bonds. Nonpolar molecules do not have an affinity for water or other polar molecules.

Why are cell membranes composed primarily of hydrophobic molecules?

Anwser: In order to perform their function of separating the aqueous solutions outside cells from the aqueous solutions inside cells, cell membranes cannot be soluble in water.

Explanation: If cell membranes were hydrophilic, they would break down and dissolve in the presence of water, rendering them useless as a barrier.

Sucrose has a molecular mass of 342 daltons. To make a 2-molar (2 M) solution of sucrose, __________.

Anwser: stir 342 g of sucrose in water to dissolve the sugar, and then add enough water to bring the total volume of the solution up to 0.5 L

Explanation: Or you could stir 684 g of sucrose in water to dissolve the sugar, and then add enough water to bring the total volume of the solution up to 1 L.

A mole of ethyl alcohol weighs 46 g. How many grams of ethyl alcohol are needed to produce 1 L of a 2-millimolar (2 mM) solution?

Anwser: 0.092 g

Explanation: This would produce a 0.002 M or a 2 mM solution.

An acid is __________.

Answer: a compound that donates hydrogen ions to a solution.

Explanation: An acid donates hydrogen ions to a solution.

Adding acid tends to __________ of a solution.

Anwser: increase the hydrogen ion concentration and lower the pH

Explanation: Because pH is a negative log, its value is inversely proportional to the hydrogen ion concentration.

Which of the following dissociations is that of an acid?

Answer: HF → H⁺ + F^–

Explanation: Hydrofluoric acid (HF) dissociates into a hydrogen ion and a fluoride ion.

A glass of grapefruit juice, at pH 3, contains __________ H⁺ as a glass of tomato juice, at pH 4.

Answer: ten times as much.

Explanation: The pH scale is based on powers of 10. The change from any pH value to the next smaller value represents a tenfold increase in the hydrogen ion concentration.

A solution at pH 6 contains __________ than the same amount of solution at pH 8.

Anwser:100 times more H⁺

Explanation: Each pH unit change represents a tenfold difference in the hydrogen ion concentration; thus, 10 × 10 = 100.

Adding a base tends to __________ of a solution.

Answer: lower the hydrogen ion concentration and increase the pH.

Explanation: A substance that reduces the hydrogen ion concentration is a base. Reducing the hydrogen ion concentration increases the pH.

Why is the increasing amount of carbon dioxide being taken up by the oceans a cause for concern?

Anwser: More carbon dioxide causes an increase in carbonic acid (H₂CO₃), which leads to a decrease in the concentration of carbonate ion (CO₃^2–).

Explnation: As seawater becomes more acidic, carbonate ion concentration decreases. The decrease in the availability of carbonate ion makes it more difficult for marine organisms to secrete calcium carbonate shells.

The absorption of human-generated CO₂ by the oceans __________.

Answer: increases the hydrogen ion concentration in the oceans but decreases the carbonate ion concentration and threatens the livability of the oceans for organisms that produce calcium carbonate shells.

Explanation: The absorption of CO₂ by the oceans causes an increase in the carbonic acid and hydrogen ion concentration (lower pH). The extra hydrogen ions bind with the carbonate ion to form bicarbonate. This reduces the amount of carbonate ions available for calcification, the production of calcium carbonate (CaCO₃) by many marine organisms, including reef-building corals and animals that build shells.