Ch 3: Water and Life
A molecule that has all nonpolar covalent bonds would be __________. (Concept 3.2) hydrophilic hydrophobic acidic basic (alkaline)
hydrophobic (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.)
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? (Concept 3.2) 92 g 9.2 g 0.92 g 0.092 g
0.092 g This would produce a 0.002 M or a 2 mM solution.
About _____ molecules in a glass of water are dissociated.
1 in 500,000,000
A pH of 6 is how many times more acidic than a pH of 9? 3 30 100 300 1,000
1,000 (A pH of 6 is 10 times more acidic than 7, which is 10 times more acidic than 8, which is 10 times more acidic than 9. 10 x 10 x 10 = 1,000.)
What is the hydrogen ion (H+) concentration of a solution of pH 8? 10-6 M 8 x 10-6 M 10-8 M 8 M
10-8 M
A solution at pH 6 contains __________ than the same amount of solution at pH 8. (Concept 3.3) 2 times more H+ 4 times more H+ 100 times more H+ 4 times less H+
100 times more H+ (Each pH unit change represents a tenfold difference in the hydrogen ion concentration; thus 10 × 10 = 100.)
If the molecular mass of a carbon atom is 12, the mass of a hydrogen atom is 1, and the mass of an oxygen atom is 16 daltons, how many molecules does one mole of table sugar (sucrose; C12H22O11) contain? 6.02 x 1023/342 6.02 x 1023 (6.02 x 1023)(342) 45 342
6.02 x 1023 (In fact, this is the number of molecules in one mole of any substance.)
Select the statement that best describes a buffer.
A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added.
Select the statement that best describes a buffer. A buffer stabilizes the pH of a solution by preventing acids or bases from dissociating. A buffer prevents the pH of a solution from changing when an acid or base is added. A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added. A buffer causes acidic solutions to become alkaline, and alkaline solutions to become acidic. Buffered solutions are always neutral, with a pH of 7.
A buffer resists change in pH by accepting hydrogen ions when acids are added to the solution and donating hydrogen ions when bases are added. (In this fashion, buffers minimize the change in the pH of a solution.)
Which of the following effects can occur because of the high surface tension of water? A raft spider can walk across the surface of a small pond. Organisms can resist temperature changes, although they give off heat due to chemical reactions. Sweat can evaporate from the skin, helping to keep people from overheating. Lakes cannot freeze solid in winter, despite low temperatures.
A raft spider can walk across the surface of a small pond.
Which of the following dissociations is that of an acid? (Concept 3.3) NaOH → Na+ + OH- H2O → H+ + OH- NH3 + H+ → NH4+ HF → H+ + F-
HF → H+ + F- (Hydrofluoric acid (HF) dissociates into a hydrogen ion and a fluoride ion.)
What do cohesion, surface tension, and adhesion have in common with reference to water? (Concept 3.2) All are properties related to hydrogen bonding. All have to do with ionic interactions. All are results of the structure of the hydrogen atom. All are produced by covalent bonding.
All are properties related to hydrogen bonding. ( The extraordinary qualities of water are emergent properties resulting from hydrogen bonding.)
Cells are surrounded by water, and cells themselves consist of about 70-95% water. Which of the following occurs as a result? (Concept 3.1) -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. -All of the listed responses are correct.
All of the listed responses are correct. (All of the listed responses result from the extraordinary characteristics of water.)
How does the polarity of water contribute to its ability to dissolve so many substances? (Concept 3.2) -Natural water has a pH of approximately 5.6, which is slightly acidic. Acids can dissolve more substances than bases can. -Because it is polar, water forms ionic bonds with the ions in substances such as NaCl (salt). -Water's polarity allows it to form covalent bonds with many substances -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.
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. (Polar water molecules surround the individual ions or charged molecules, separating and shielding the ions or molecules from one another.)
A substance that minimizes changes in the concentration of H+ and OH- in a solution is a __________. (Concept 3.3) NaCl hydrophobic molecule strong acid Buffer
Buffer (Buffers are substances that minimize changes in the concentration of hydrogen ions and hydroxide ions in a solution; therefore, buffers maintain a relatively constant pH.)
If the pH of a solution is decreased from 9 to 8, it means that the concentration of _____. H+ has increased tenfold (10X) compared to what it was at pH 9 OH- has increased tenfold (10X) compared to what it was at pH 9 H+ has decreased to one-tenth (1/10) what it was at pH 9 H+ has doubled compared to what it was at pH 9
H+ has increased tenfold (10X) compared to what it was at pH 9
Which of these is the correct equation for the dissociation of water?
H2O + H2O <==> H3O+ + OH-
Which of the following accurately relates the emergent properties of water to the effects of global warming in the Arctic? (Concept 3.2) -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. -Although it is feared that sea ice around Alaska and northern Canada may be greatly reduced by atmospheric warming, the high specific heat of water has so far buffered these sea ice communities from significant impacts. -An increase in water temperature due to global warming will cause the sea ice formed in the Arctic to be denser and less buoyant. -Although a significant increase of air temperature has occurred in the Arctic over the past 50 years, the specific heat of water has thus far buffered against any significant increases in the Arctic ocean temperatures.
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. (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. )
Which of the following occurs because molecules of water are farther apart in ice than in liquid water? (Concept 3.2) Ice vaporizes before liquid water does. Ice floats. Ice is denser than liquid water. Ice expands when it melts.
Ice floats. (Because water molecules in ice are farther apart than in liquid water, ice is less dense, and therefore, it floats.)
Why are cell membranes composed primarily of hydrophobic molecules? (Concept 3.2) -In order to maintain a proper pH, cell membranes must be hydrophobic. -In order to perform their function of separating the aqueous solutions outside of cells from the aqueous solutions inside of cells, cell membranes cannot be soluble in water. -Cell membranes must be hydrophobic in order to allow polar and charged molecules to enter and leave the cell. -Cell membranes must be composed of polar molecules in order to interact with the aqueous solutions inside of cells.
In order to perform their function of separating the aqueous solutions outside of cells from the aqueous solutions inside of cells, cell membranes cannot be soluble in water. (If cell membranes were hydrophilic, they would break down and dissolve in the presence of water, rendering them useless as a barrier.)
Why is the increasing amount of carbon dioxide being taken up by the oceans a cause for concern? (Concept 3.3) -More carbon dioxide causes an increase in carbonic acid (H2CO3), which leads to a decrease in the concentration of carbonate ion (CO32-). -There is no cause for concern. Carbonic acid (H2CO3) is an excellent buffer and will help keep the pH of seawater constant. -More carbon dioxide causes an increase in carbonic acid (H2CO3), which leads to an increase in the concentration of carbonate ion (CO32-). -The buffering action of carbonic acid (H2CO3) causes the pH of seawater to rise.
More carbon dioxide causes an increase in carbonic acid (H2CO3), which leads to a decrease in the concentration of carbonate ion (CO32-). (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.)
Why does ice float in liquid water? The high surface tension of liquid water keeps the ice on top. The crystalline lattice of ice causes it to be denser than liquid water. Stable hydrogen bonds keep water molecules of ice farther apart than water molecules of liquid water. The ionic bonds between the molecules in ice prevent the ice from sinking.
Stable hydrogen bonds keep water molecules of ice farther apart than water molecules of liquid water.
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? (Concept 3.2) -Living organisms would have to be much smaller. -Organisms would be able to live in a much wider range of temperatures. -Warm-blooded organisms would require less insulation such as fur or feathers. -Systems for temperature regulation would have to be much more efficient.
Systems for temperature regulation would have to be much more efficient. (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.)
If water were NOT a polar molecule, how would the effects of global warming differ from those currently observed or predicted to occur in the future? (Concept 3.2) -If water molecules were nonpolar, then water vapor would be less effective as a greenhouse gas and the effects of global warming would be less extreme. -The effects would be worse because a loss of the polar molecular structure would lead to a greater amount of heat absorbed by water molecules and, thus, an increase in its specific heat. -If water were nonpolar, the effects on global warming would be only slightly worse because there are other polar molecules that can moderate climate as water does. -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.
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. (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.)
An acid is __________. (Concept 3.3) a material that resists changes in the pH of a solution any compound with a pH a compound that donates hydrogen ions to a solution any compound that accepts hydrogen ions
a compound that donates hydrogen ions to a solution (An acid donates hydrogen ions to a solution.)
Water has __________ than other liquids such as ethanol , reflecting its capacity to absorb large amounts of heat. (Concept 3.2) lower specific heat a lower capacity for forming hydrogen bonds a higher boiling point a lower heat of vaporization
a higher boiling point (More heat is needed to vaporize 1 g of water than most other liquids.)
Sodas typically contain sugar, flavorings, coloring agents, and carbon dioxide dissolved in water. The best term to describe this mixture would be _____. an aqueous solvent a solute a solvent an aqueous solution a suspension
an aqueous solution (For solutions where water is the solvent, the term "aqueous solution" is used.)
Many of water's emergent properties, such as its cohesion, its high specific heat, and its high heat of vaporization, result from the fact that water molecules _____. are extremely large tend to repel each other are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively are very small are in constant motion
are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively
Many of water's emergent properties, such as its cohesion, its high specific heat, and its high heat of vaporization, result from the fact that water molecules _____. are extremely large are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively are in constant motion tend to repel each other are very small
are attracted to each other by partial negative and positive charges on the oxygen and hydrogen atoms, respectively (The formation of hydrogen bonds between the positive and negative regions of different water molecules accounts for most of water's unique properties.)
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 __________. (Concept 3.2) -both caused by water's ability to form covalent bonds with hydrophobic substances -due to water's partial charges and low molecular mass, respectively -both caused by water's partial charges -both caused by water's two electron shells
both caused by water's partial charges (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 __________. (Concept 3.2) cohesion specific heat surface tension hydration shells
cohesion (Cohesion is a consequence of hydrogen bonding between water molecules.)
Which action would involve the greatest transfer of heat? (Concept 3.2) cooling 10 g of water from 80°C to 40°C changing the temperature of 1 g of water from 10°C to 90°C evaporating 1 g of water at 25°C condensing 5 g of steam to liquid water
condensing 5 g of steam to liquid water (This would release about 2,900 calories (580 calories/gram × 5 grams).)
The transfer of a hydrogen atom from one water molecule to another is referred to as
dissociation.
The tendency of an atom to pull electrons toward itself is referred to as its _____. ionic potential covalency tonicity polarity electronegativity
electronegativity
Each water molecule is joined to _____ other water molecules by ____ bonds. two ... polar covalent three ... ionic two ... hydrogen four ... hydrogen four ... polar covalent
four ... hydrogen
Sweating has a cooling effect because of water's high __________. (Concept 3.2) surface tension heat of vaporization buffering capacity specific heat
heat of vaporization (Water's high heat of vaporization results in evaporative cooling because when water evaporates, the surface on which it rests cools down.)
Because organisms are made primarily of water, they resist rapid temperature changes. This useful quality is based on water's _____. cohesion lower density in the solid phase ability to form colloids buffering activity high specific heat
high specific heat (Water has a high specific heat, meaning that a relatively large amount of heat must be added or removed in order to get the temperature of the water to change significantly.)
Which type of bond must be broken for water to vaporize? ionic bonds hydrogen bonds both polar covalent bonds and hydrogen bonds polar covalent bonds
hydrogen bonds
Water molecules have a polarity, which allows them to be electrically attracted to other water molecules and other polar molecules by weak chemical bonds known as _____. nonpolar covalent bonds ionic bonds hydrogen bonds Van der Waals interactions polar covalent bonds
hydrogen bonds (The polarity of a water molecule allows the oxygen of one water molecule to bond weakly to the hydrogen of another water molecule)
What are nonpolar molecules that cluster away from water molecules called? (Concept 3.2) ionic hydrophilic hydrophobic None of the listed responses is correct.
hydrophobic (Substances that are nonionic and nonpolar repel water.)
A water molecule that loses a hydrogen ion is referred to as a A water molecule that gains a hydrogen becomes a
hydroxide ion. hydronium ion.
Adding acid tends to __________ of a solution. (Concept 3.3) decrease the hydrogen ion concentration and lower the pH increase the hydrogen ion concentration and lower the pH increase the hydrogen ion concentration and raise the pH decrease the hydrogen ion concentration and raise the pH
increase the hydrogen ion concentration and lower the pH (Because pH is a negative log, its value is inversely proportional to the hydrogen ion concentration.)
The absorption of human-generated CO2 by the oceans __________. (Concept 3.3) -increases the oceans' acidity and pH -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 -increases the oceanic concentration of carbonic acid -reduces the carbonate ion concentration in the oceans and threatens calcifying organisms in marine ecosystems
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 (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.)
An acid is a substance that _____.
increases the hydrogen ion concentration of an aqueous solution (As an acid dissociates, it donates a hydrogen ion to the solution)
An acid is a substance that _____. forms covalent bonds with other substances contains hydrogen reduces the hydrogen ion concentration of a solution is a versatile solvent increases the hydrogen ion concentration of an aqueous solution
increases the hydrogen ion concentration of an aqueous solution (As an acid dissociates, it donates a hydrogen ion to the solution.)
The amount of energy that must be absorbed or lost to raise or lower the temperature of 1 g of liquid water by 1°C _____. depends on the initial temperature of the water sample is 1 kilocalorie is 1,000 kilocalories is 1 calorie is 1,000 joules is 1,000 calories
is 1 calorie (The specific heat of liquid water is 1 cal/g/°C.)
The tendency of water molecules to stay close to each other as a result of hydrogen bonding __________. (Concept 3.2) -provides the surface tension that allows small animals to move across a water surface -helps to keep water moving through the vessels in a tree trunk -is called cohesion -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
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 (All of the choices reflect results of the cohesiveness of water molecules.)
Adding a base tends to __________ of a solution. (Concept 3.3) increase the hydrogen ion concentration and lower the pH lower the hydrogen ion concentration and lower the pH lower the hydrogen ion concentration and increase the pH increase the hydrogen ion concentration and increase the pH
lower the hydrogen ion concentration and increase the pH (A substance that reduces the hydrogen ion concentration is a base. Reducing the hydrogen ion concentration increases the pH.)
A solution contains 0.0000001 (10-7) moles of hydroxyl ions [OH-] per liter. Which of the following best describes this solution?
neutral
concentration of 10-12 M? What is the pH of a solution with a hydroxyl ion (OH-) concentration of 10-12 M? pH 12 pH 10 pH 4 pH 2
pH 2
The unequal sharing of electrons within a water molecule makes the water molecule _____. have a low surface tension polar change easily from a liquid to gaseous form ionic hydrophobic
polar
Water is a very versatile solvent because water molecules are __________. (Concept 3.2) hydrophobic polar nonpolar ionic
polar (Because molecules of polar solvents have a positive and a negative pole, polar solvents are excellent solvents for ions and for other polar materials.)
Based on your knowledge of the polarity of water molecules, the solute molecule depicted in the center of 4 water molecules, is most likely _____. positively charged nonpolar negatively charged without charge
positively charged
The reason that coastal climates are more moderate than inland climates primarily water's high __________. (Concept 3.2) surface tension specific heat adhesion heat of vaporization
specific heat (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.)
Sucrose has a molecular mass of 342 daltons. To make a 2-molar (2 M) solution of sucrose, __________. (Concept 3.2) -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 0.5 L -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 -stir 342 g of sucrose in water to dissolve the sugar, and then add enough water to bring the total volume of the solution to 1 L -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 2 L
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 (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.)
Rank, from low to high, the pH of blood, stomach acid, and urine.
stomach acid, urine, blood
Most acid precipitation results from the combination of _____ with water in the atmosphere, forming strong acids that fall with rain or snow. ammonium buffers sulfur oxides and nitrogen oxides ozone carbon dioxide
sulfur oxides and nitrogen oxides (These compounds react with water in the atmosphere to form sulfuric acid and nitric acid.)
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? (Concept 3.2) its polarity surface tension adhesion None of the listed responses is correct.
surface tension (Water has a greater surface tension, a measure of how difficult it is to break the surface of a liquid, than most other liquids.)
A glass of grapefruit juice, at pH 3, contains __________ H+ as a glass of tomato juice, at pH 4. (Concept 3.3) one-tenth as much half as much twice as much ten times as much
ten times as much (The pH scale is a base-10 logarithmic scale. The change from any pH value to the next smaller value represents a tenfold increase in the hydrogen ion concentration.)
Water is a polar molecule. What does this statement mean? (Concept 3.1) -that water molecules are linear, like a pole -that the atoms in water have equal electronegativities -that atoms in the molecule have partial charges as a result of unequal sharing of electrons in a covalent bond -that water is one of the many hydrophobic molecules
that atoms in the molecule have partial charges as a result of unequal sharing of electrons in a covalent bond (In the case of water, the oxygen is slightly negative and the hydrogen atoms are slightly positive.)
Adhesion is best described as which of the following? (Concept 3.2) -the clinging of one substance to another substance -a property of water that helps moderate Earth's temperature -the process that contributes to the transport of water and dissolved nutrients in plants by causing water molecules to tug on other water molecules -the process by which a crystalline lattice forms
the clinging of one substance to another substance (Adhesion is the attraction of one substance to another.)
The partial negative charge in a molecule of water occurs because _____. the oxygen atom has two pairs of electrons in its valence shell that are not neutralized by hydrogen atoms the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus the oxygen atom donates an electron to each of the hydrogen atoms one of the hydrogen atoms donates an electron to the oxygen atom
the electrons shared between the oxygen and hydrogen atoms spend more time around the oxygen atom nucleus than around the hydrogen atom nucleus
The amount of heat required to convert 1 g of any substance from the liquid to the gaseous state is defined as __________. (Concept 3.2) the specific heat of that substance 1 calorie the heat of vaporization of that substance surface tension
the heat of vaporization of that substance (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.)
In a group of water molecules, hydrogen bonds form between which of the following? (Concept 3.1) -the oxygen atoms in different water molecules -two hydrogen atoms in different water molecules -the hydrogen atoms in a single water molecule -the oxygen atom in one water molecule and a hydrogen atom in another water molecule
the oxygen atom in one water molecule and a hydrogen atom in another water molecule (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.)
The amount of heat required to change the temperature of 1 g of any substance by 1°C is defined as __________. (Concept 3.2) 1 kilocalorie 1 calorie the heat of vaporization of that substance the specific heat of that substance
the specific heat of that substance (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 partial charges on a water molecule occur because of __________. (Concept 3.1) -covalent bonding -the achievement of a stable configuration by one atom of a bond but not by the other partner -widespread ionization -the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule
the unequal sharing of electrons between the hydrogen and the oxygen atoms of a water molecule (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.)
