Chapter 3: Water and Life

kilocalories (kcal)

1,000 cal, is the quantity of heat required to raise the temperature of 1 kilogram (kg) of water by 1°C. (The "Calories" on food packages)

cohesive behavior, ability to moderate temperature, expansion upon freezing, and versatility as a solvent

4 emergent properties of water

If enough of a base is added to raise the OH- concentration to 10-4 M, it will cause the H+ concentration to drop to 10-10 M.

A base has the opposite effect, increasing OH- concentration but also reducing H+ concentration by the formation of water.

much of the heat is used to disrupt hydrogen bonds before the water molecules can begin moving faster.

A calorie of heat causes a relatively small change in the temperature of water ________________

solution

A liquid that is a completely homogeneous mixture of two or more substances

neutral

A solution in which the H+ and OH- concentrations are equal

base

A substance that reduces the hydrogen ion concentration of a solution

The hydrophobic substance repels water, perhaps helping to keep the ends of the legs from becoming coated with water and breaking through the surface. If the legs were coated with a hydrophilic substance, water would be drawn up them, possibly making it more difficult for the water strider to walk on water.

A water strider (an insect that can walk on water) has legs that are coated with a hydrophobic substance. What might be the benefit? What would happen if the substance were hydrophilic?

CH3COOH ---> CH3COO- + H+ CH3COOH is the acid (the H+ donor) CH3COO- is the base (the H+ acceptor)

Acetic acid (CH3COOH) can be a buffer, similar to carbonic acid. Write the dissociation reaction, identifying the acid, base, H+ acceptor, and H+ donor.

H+ and OH- are very reactive. Changes in their concentrations can drastically affect a cell's proteins and other complex molecules.

Although the dissociation of water is reversible and statistically rare, it is exceedingly important in the chemistry of life.

because of the tendency for H+ to combine with OH- , forming water

An acid not only adds hydrogen ions to a solution, but also removes hydroxide ions

heat

An ice cube cools a drink not by adding coldness to the liquid, but by absorbing thermal energy from the liquid as the ice itself melts. Thermal energy in transfer from one body of matter to another is defined as _______

Hydrophilic

Any substance that has an affinity for water (from the Greek hydro, water, and philos, loving)

kinetic energy

Anything that moves has ___________________, the energy of motion. Atoms and molecules have kinetic energy because they are always moving, although not necessarily in any particular direction.

evaporative cooling

As a liquid evaporates, the surface of the liquid that remains behind cools down (its temperature decreases). This __________________________________ occurs because the "hottest" molecules, those with the greatest kinetic energy, are the most likely to leave as gas.

The hydrogen bonds keep the molecules at "arm's length," far enough apart to make ice about 10% less dense (10% fewer molecules in the same volume) than liquid water at 4°C. When ice absorbs enough heat for its temperature to rise above 0°C, hydrogen bonds between molecules are disrupted. As the crystal collapses, the ice melts and molecules have fewer hydrogen bonds, allowing them to slip closer together.

As the temperature falls from 4°C to 0°C, water begins to freeze because more and more of its molecules are moving too slowly to break hydrogen bonds. At 0°C, the molecules become locked into a crystalline lattice, each water molecule hydrogenbonded to four partners

expanding as it warms and contracting as it cools

At temperatures above 4°C, water behaves like other liquids, __________________________________

The oxygens of the water molecules have regions of partial negative charge that are attracted to sodium cations. The hydrogen regions are partially positively charged and are attracted to chloride anions.

At the surface of each crystal of salt, the sodium and chloride ions are exposed to the solvent. These ions and regions of the water molecules are attracted to each other due to their opposite charges.

Cohesion

Attraction between molecules of the same substance

100,000

Compared with a basic solution at pH 9, the same volume of an acidic solution at pH 4 has _________ times as many hydrogen ions (H+ ).

Hydrogen bonds hold neighboring water molecules together. This cohesion helps chains of water molecules move upward against gravity in water-conducting cells as water evaporates from the leaves. Adhesion between water molecules and the walls of the water-conducting cells also helps counter gravity

Describe how properties of water contribute to the upward movement of water in a tree.

-evaporation of water from the leaves of a plant helps keep the tissues in the leaves from becoming too warm in the sunlight. -Evaporation of sweat from human skin dissipates body heat and helps prevent overheating on a hot day or when excess heat is generated by strenuous activity. High humidity on a hot day increases discomfort because the high concentration of water vapor in the air inhibits the evaporation of sweat from the body.

Evaporative cooling of water contributes to the stability of temperature in lakes and ponds and also provides a mechanism that prevents terrestrial organisms from overheating.

High humidity hampers cooling by suppressing the evaporation of sweat.

Explain the saying "It's not the heat; it's the humidity."

Due to its two polar covalent bonds, a water molecule has four regions of partial charge: two positive regions on the two hydrogens and two negative regions on the oxygen atom. Each of these can bind to a region of opposite partial charge on another water molecule.

Explain why the central water molecule can hydrogen bond to four (rather than three or five) other water molecules.

The pH of the water should decrease from 7 to about 2 the pH of the acetic acid solution will decrease only a small amount, because as a weak acid, it acts (like carbonic acid) as a buffer. CH3COO- accepting the influx of H+ and becoming CH3COOH molecules.

Given a liter of pure water and a liter solution of acetic acid, what would happen to the pH, in general, if you added 0.01 mol of a strong acid to each?

[H+ ] = 0.01 M = 10-2 M, so pH = 2

HCl is a strong acid that dissociates in water: HCl S H+ + Cl- . What is the pH of 0.01 M HCl?

heat is released when hydrogen bonds form

Heat must be absorbed in order to break hydrogen bonds

As water freezes, it expands because water molecules move farther apart in forming ice crystals. When there is water in a crevice of a boulder, expansion due to freezing may crack the boulder

How can the freezing of water crack boulders?

The water adheres to the cat's tongue, this is due to one of water's properties called adhesion.

How do cats drink? Scientists using highspeed video have shown that cats use an interesting technique to drink aqueous substances like water and milk. Four times a second, the cat touches the tip of its tongue to the water and draws a column of water up into its mouth, which then shuts before gravity can pull the water back down. Describe how the properties of water allow cats to drink in this fashion, including how water's molecular structure contributes to the process.

We would measure out 342 g of sucrose 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 sucrose.

How would we make a liter (L) of solution consisting of 1 mol of sucrose dissolved in water?

This oxygen is attracted to a slight positive charge on the lysozyme molecule. This hydrogen is attracted to a slight negative charge on the lysozyme molecule.

Human lysozyme is a protein found in tears and saliva that has antibacterial action. This model shows the lysozyme molecule (purple) in an aqueous environment. Ionic and polar regions on the protein's surface attract the partially charged regions on water molecules.

however, the pH decrease is only from 7.4 to 7.3.

If 0.01 mol of a strong acid is added to a liter of pure water, the pH drops from 7.0 to 2.0. If the same amount of acid is added to a liter of blood

But when the H+ concentration in blood begins to rise (when pH drops), the reaction proceeds to the left, with HCO3 - (the base) removing the hydrogen ions from the solution and forming H2CO3.

If the H+ concentration in blood begins to fall (that is, if pH rises), the reaction proceeds to the right and more carbonic acid dissociates, replenishing hydrogen ions.

the floating ice insulates the liquid water below, preventing it from freezing and allowing life to exist under the frozen surface.

If water did not form hydrogen bonds, what would happen to the shrimp's habitat?

Due to intermolecular hydrogen bonds, water has a high specific heat When water is heated, much of the heat is absorbed in breaking hydrogen bonds before the water molecules increase their motion and the temperature increases. Conversely, when water is cooled, many H bonds are formed, which releases a significant amount of heat. This release of heat can provide some protection against freezing of the plants' leaves, thus protecting the cells from damage.

In agricultural areas, farmers pay close attention to the weather forecast. Right before a predicted overnight freeze, farmers spray water on crops to protect the plants. Use the properties of water to explain how this method works. Be sure to mention why hydrogen bonds are responsible for this phenomenon.

10^-14

In any aqueous solution at 25°C, the product of the H+ and OH- concentrations is constant at ________

Floating ice becomes a barrier that insulates the liquid water below from the colder air. E.g. a type of shrimp called krill

In ice, each molecule is hydrogen-bonded to four neighbors in a three-dimensional crystal. Because the crystal is spacious, ice has fewer molecules than an equal volume of liquid water. In other words, ice is less dense than liquid water.

554 million

In pure water, only one water molecule in every ____________________ is dissociated

-some molecules in cells are so large that they do not dissolve. -Cotton consists of giant molecules of cellulose, a compound with numerous regions of partial positive and partial negative charges that can form hydrogen bonds with water. Water adheres to the cellulose fibers. Thus, a cotton towel does a great job of drying the body, yet it does not dissolve in the washing machine. -Cellulose is also present in the walls of water-conducting cells in a plant; the adhesion of water to these hydrophilic walls helps water move up the plant against gravity.

In some cases, substances can be hydrophilic without actually dissolving.

two regions of partial negative charge

In water, the oxygen of the molecule has ___________________________ (δ-)

mole (mol), 6.02 x 10^23

Just as a dozen always means 12 objects, a ______________ represents an exact number of objects: _______________, which is called Avogadro's number.

In contrast, ammonia is a weak base. The double arrows in the reaction for ammonia indicate that the binding and release of hydrogen ions are reversible reactions, although at equilibrium there will be a fixed ratio of NH4 + to NH3.

Notice that single arrows were used in the reactions for HCl and NaOH. These compounds dissociate completely when mixed with water, so hydrochloric acid is called a strong acid and sodium hydroxide a strong base.

hydrogen ion (H+)

Occasionally, a hydrogen atom participating in a hydrogen bond between two water molecules shifts from one molecule to the other. When this happens, the hydrogen atom leaves its electron behind, and what is actually transferred is a _____________________, a single proton with a charge of 1+.

0.239 cal

One joule equals ____________ cal

One such base is sodium hydroxide (NaOH), which in water dissociates into its ions: NaOH → Na+ + OH-

Other bases reduce the H+ concentration indirectly by dissociating to form hydroxide ions, which combine with hydrogen ions and form water.

Water molecules have a polar arrangement of the oxygen and hydrogen atoms—one side (hydrogen) has a positive electrical charge and the other side (oxygen) had a negative charge. This allows the water molecule to become attracted to many other different types of molecules.

Several emergent properties of water contribute to the suitability of the environment for life. Describe how the ability of water to function as a versatile solvent arises from the structure of water molecules.

basic solutions

Solutions with a higher concentration of OH- than H+

Ammonia (NH3), for instance, acts as a base when the unshared electron pair in nitrogen's valence shell attracts a hydrogen ion from the solution, resulting in an ammonium ion (NH4 + ): NH3 + H+ ⇌ NH4 +

Some bases reduce the H+ concentration directly by accepting hydrogen ions.

hydrophobic

Substances that are nonionic and nonpolar (or otherwise cannot form hydrogen bonds) actually seem to repel water; these substances are said to be_____________________ (from the Greek phobos, fearing)

specific heat

The ____________________ of a substance is defined as the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C

A liter of blood would contain 7.8x10^13 molecules of ghrelin. (1.3x10^-10 moles per liter x 6.02x10^23 molecules per mole)

The concentration of the appetite-regulating hormone ghrelin is about 1.3 x 10^-10 M in the blood of a fasting person. How many molecules of ghrelin are in 1 L of blood?

close to 7

The internal pH of most living cells is

thermal energy

The kinetic energy associated with the random movement of atoms or molecules is called ___________________

a mole of one substance has exactly the same number of molecules as a mole of any other substance. If the molecular mass of substance A is 342 daltons and that of substance B is 10 daltons, then 342 g of A will have the same number of molecules as 10 g of B.

The practical advantage of measuring a quantity of chemicals in moles is that _____________________________

hydronium ion (H3O+ or H+)

The proton binds to the other water molecule, making that molecule a __________________________________.

hydration shell

The sphere of water molecules around each dissolved ion

hydroxide ion (OH-)

The water molecule that lost a proton is now a _____________________________, which has a charge of 1-.

If extremophiles can survive in such intense, hot, and acidic environments on earth, then it can be concluded by astrobiologists that extremophiles could possibly be able to survive on other planets, with similar intense conditions.

This chapter explains how the emergent properties of water contribute to the suitability of the environment for life. Until fairly recently, scientists assumed that other physical requirements for life included a moderate range of temperature, pH, atmospheric pressure, and salinity, as well as low levels of toxic chemicals. That view has changed with the discovery of organisms known as extremophiles, which have been found flourishing in hot, acidic sulfur springs, around hydrothermal vents deep in the ocean, and in soils with high levels of toxic metals. Why would astrobiologists be interested in studying extremophiles? What does the existence of life in such extreme environments say about the possibility of life on other planets?

580

To evaporate 1 g of water at 25°C, about _______ cal of heat is needed—nearly double the amount needed to vaporize a gram of alcohol or ammonia

less

Water is one of the few substances that are __________ dense as a solid than as a liquid

absorbing heat from air that is warmer and releasing the stored heat to air that is cooler.

Water moderates air temperature by _____________________

Cohesion due to hydrogen bonds between water molecules helps hold together the column of water within the cells. Adhesion of the water to cell walls by hydrogen bonds helps resist the downward pull of gravity. Evaporation from leaves pulls water upward from the roots through water-conducting cells.

Water transport in plants. Because of the properties of cohesion and adhesion, the tallest trees can transport water more than 100 m upward—approximately one-quarter the height of the Empire State Building in New York City.

Both global warming and ocean acidification are caused by increasing levels of carbon dioxide in the atmosphere, the result of burning fossil fuels.

What do climate change and ocean acidification have in common?

Electronegativity is the attraction of an atom for the electrons of a covalent bond. Because oxygen is more electronegative than hydrogen, the oxygen atom in H2O pulls electrons toward itself, resulting in a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. Atoms in neighboring water molecules with opposite partial charges are attracted to each other, forming a hydrogen bond.

What is electronegativity, and how does it affect interactions between water molecules?

The covalent bonds of water molecules would not be polar, so no regions of the molecule would carry partial charges and water molecules would not form hydrogen bonds with each other.

What would be the effect on the properties of the water molecule if oxygen and hydrogen had equal electronegativity?

mass

When carrying out experiments, we use ________ to calculate the number of molecules.

1/20

When water is in its liquid form, its hydrogen bonds are very fragile, each only about _______ as strong as a covalent bond.

expands

While other materials contract and become denser when they solidify, water ______________.

surface tension

a measure of how difficult it is to stretch or break the surface of a liquid

acid

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-

buffer

a substance that minimizes changes in the concentrations of H+ and OH- in a solution, allows biological fluids to maintain a relatively constant pH despite the addition of acids or bases.

weak acids

acids that reversibly release and accept back hydrogen ions. An example is carbonic acid (H2CO3)

the swimming pool contains more thermal energy because of its much greater volume.

although the pot of coffee has a much higher temperature than, say, the water in a swimming pool

A large body of water can absorb and store a huge amount of heat from the sun in the daytime and during summer while warming up only a few degrees. At night and during winter, the gradually cooling water can warm the air.

capability of water to moderate air temperatures in coastal areas

ocean acidification

decreasing pH of ocean waters due to absorption of excess atmospheric CO2 from the burning of fossil fuels

solvent

dissolving agent of a solution

each hydrogen has a partial positive charge (δ+)

each hydrogen has a _______________________ (δ+)

A solution of pH 3 is not twice as acidic as a solution of pH 6, but 1,000 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.

each pH unit represents a tenfold difference in H+ and OH- concentrations. It is this mathematical feature that makes the pH scale so compact.

carbonic acid H2CO3

formed when CO2 reacts with water in blood plasma, a buffer

[H+] = 10^-7 and [OH-] = 10^-7

in a neutral solution at 25°C

polar molecule

its overall charge is unevenly distributed

extremophiles

live in extreme environments

pH scale

measurement system used to indicate the concentration of hydrogen ions (H+) in solution; ranges from 0 to 14

4.184 J

one calorie equals ____________ J

2

pH of Gastric juice (in stomach), lemon juice

11.5

pH of Household ammonia

13

pH of Household bleach

7.4

pH of Human blood, tears

8.5

pH of Inside small intestine

10.5

pH of Milk of magnesia

13.7

pH of Oven cleaner

8

pH of Seawater

4

pH of Tomato juice Beer Black coffee

3

pH of Vinegar, wine, cola

1.2

pH of battery acid

7

pH of pure water

5.6

pH of rainwater

6.7

pH of saliva

6

pH of urine

temperature

represents the average kinetic energy of the molecules in a body of matter, regardless of volume whereas the thermal energy of a body of matter reflects the total kinetic energy, and thus depends on the matter's volume.

0.6 calorie per gram and per degree Celsius

specific heat of ethyl alcohol

1 calorie per gram and per degree Celsius

specific heat of water

C12H22O11

table sugar (sucrose)

calorie (cal)

the amount of heat it takes to raise the temperature of 1 g of water by 1°C also the amount of heat that 1 g of water releases when it cools by 1°C

Adhesion

the clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds, countering the downward pull of gravity

Molarity

the number of moles of solute per liter of solution—is the unit of concentration most often used by biologists for aqueous solutions.

heat of vaporization

the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state

aqueous solution

the solute is dissolved in water; water is the solvent.

solute

the substance that is dissolved

molecular mass

the sum of the masses of all the atoms in a molecule

6.02 x 10^23

there are _______________ daltons in 1 g

vaporization

transformation from a liquid to a gas