AP Bio Chapter 3
An acid is...
a substance that increases the hydrogen ion concentration in a solution. When hydrochloric acid added water, hydrogen ions dissociate from chloride ions: HCl → H+ + Cl−. This produces an acidic solution.
Each pH unit represents...
a tenfold difference in H+ and OH− concentrations. A small change in pH indicates substantial change in H+ and OH− concentrations. A solution of pH3 is not twice as acidic as solution pH6 but a thousand times more acidic.
Because oxygen is more electronegative than hydrogen...
a water molecule is a polar molecule in which opposite ends of the molecule have opposite charges.
A water molecule is shaped like...
a wide V, with two hydrogen atoms joined to an oxygen atom by single polar covalent bonds.
Water has a relatively high heat of vaporization, with...
about 580 cal of heat required to evaporate 1 g of water at room temperature. This is double the amount of heat required to vaporize the same quantity of alcohol or ammonia.
Some bases reduce the H+ concentration directly by...
accepting hydrogen ions. Ammonia (NH3) acts as a base when the nitrogen sun shared electron pair attracts a hydrogen ion from the solution, creating an ammonium ion (NH4+): NH3 + H+ ⇔ NH4+.
Recent studies predict it will drop...
another 0.3-0.5 pH units by 2100.
Living things...
are made of primarily water, so they resist changes in temperature better than they would if composed of a liquid with a lower specific heat.
Each water molecule can form hydrogen bonds with...
as many as four neighbors.
Solutions with more OH− than H+ are...
basic solutions
To maintain cellular pH values at a constant level, biological fluids have...
buffers. Buffers resist changes in the pH of a solution when H+ or OH− is added to the solution. Buffers accept hydrogen ions from solution when they are in excess and donate hydrogen ions when they have been depleted. Buffers typically consist of a weak acid and corresponding base.
Adding certain solutes...
called acids and bases, disrupts the equilibrium and modifies the concentrations of hydrogen and hydroxide ions.
This is of great concern because...
carbonate ions are required for calcification, the production of calcium carbonate (CaCO3) by many marine organisms, including reef-building corals and animals that build shells. The disappearance of coral reef ecosystems would be a tragic loss of biological diversity.
One important buffer in human blood and other biological solutions is...
carbonic acid (H2CO3), formed when CO2 reacts with water in blood plasma. Carbonic acid dissociates to yield a bicarbonate ion (HCO3-) and a hydrogen ion (H+). The chemical equilibrium between carbonic acid and bicarbonate acts as a pH regulator. The equilibrium shifts left or right as other metabolic processes add or remove H+ from the solution. If the H+ concentration in blood begins to fall (that is, if the pH rises), the reaction proceeds to the right and more carbonic acid dissociates, replenishing the hydrogen ions. 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. Most buffers are acid-base pairs.
Hydrophobic molecules are major ingredients of...
cell membranes.
The ratio of ice to water on Earth is changing as a result of...
climate change.
As seawater acidifies, the extra hydrogen ions...
combine with carbonate ions (CO₃²-) to form bicarbonate ions (HCO3-).
Scientists predict that ocean acidification will cause carbonate concentrations in the oceans to...
decrease by 40% by the year 2100.
The pH scale is used to...
describe how acidic or basic a solution is.
A simplified way to view this process is to say that a water molecule...
dissociates into a hydrogen ion and a hydroxide ion: H2O ⇔ H+ + OH−.
Other bases reduce the H+ concentration indirectly by...
dissociating to OH−, which then combines with H+ to form water.
Because hydrogen and hydroxide ions are very reactive, changes in their concentrations can...
drastically affect the chemistry of a cell.
Water is the only common substance in the natural environment that...
exists in all three physical states of matter: solid, liquid, and gas.
Measuring in moles allows scientists to combine substances in...
fixed ratios of molecules.
Once we determine the molecular mass of a molecule such as sucrose, we can use the same number but with the unit...
gram.
At equilibrium, the concentration of water molecules...
greatly exceeds the concentration of H+ and OH−.
Each dissolved ion is surrounded by a sphere of water molecules, a...
hydration shell.
Water's high specific heat is due to...
hydrogen bonding. Heat must be absorbed to break hydrogen bonds, and heat is released when hydrogen bonds form. The investment of 1 calorie of heat causes relatively little change in the temperature of water because much of the energy is used to disrupt hydrogen bonds, not speed up the movement of water molecules.
The heat of vaporization is high because...
hydrogen bonds must be broken before a water molecule can evaporate from the liquid.
The slightly negative regions of one water molecule are attracted to the slightly positive regions of nearby water molecules, forming...
hydrogen bonds.
Substances that have no affinity for water are...
hydrophobic (water-fearing).
Hydrophilic substances are dominated by...
ionic or polar bonds.
When water reaches 0°C...
it becomes locked into a crystalline lattice, with each water molecule bonded to four partners
Water is not a universal solvent, but...
it is very versatile because of the polarity of water molecules.
Water is an effective solvent because...
it readily forms hydrogen bonds with charged and polar covalent molecules. For example, when a crystal of salt (NaCl) is placed in water, the Na+ cations interact with the partial negative charges of the oxygen regions of water molecules. The Cl− anions interact with the partial positive charges of the hydrogen regions of water molecules. Eventually, water dissolves all the ions, resulting in a solution with two solutes: sodium and chloride ions.
Water begins to freeze when...
its molecules are no longer moving vigorously enough to break their hydrogen bonds.
Evaporative cooling moderates temperature in...
lakes and ponds.
At temperatures higher than 4°C, water behaves...
like other liquids, expanding as it warms and contracting as it cools.
Even large molecules...
like proteins, can dissolve in water if they have ionic and polar regions.
The concentration of a material in solution is called its...
molarity.
We know the mass of each atom in a given molecule, so we can calculate its...
molecular mass, which is the sum of the masses of all the atoms in a molecule.
We measure the number of molecules in units called...
moles (mol).
solutions in which the concentrations of OH- and H+ are equal are...
neutral.
Hydrophobic substances are...
nonionic and have nonpolar covalent bonds. Because no regions consistently have partial or full charges, water molecules cannot form hydrogen bonds with hydrophobic molecules. Oils such as vegetable oil are hydrophobic because the dominant bonds, carbon-carbon and carbon-hydrogen, share electrons equally.
Vaporization...
occurs when a molecule moves fast enough to overcome the attraction of other molecules in the liquid.
This weak acid lowers the pH of seawater, a process known as...
ocean acidification.
Water has an unusually high specific heat compared to other substances. Water resists changes in temperature because...
of its high specific heat. In other words, water absorbs or releases a relatively large quantity of heat for each degree of temperature change.
Water has a variety of unusual properties because...
of the attraction between polar water molecules.
Over 800 planets have been found outside our solar system, and there is evidence for the presence of water vapor on...
one or two of them.
The oxygen region of the molecule has a...
partial negative charge (δ-), and the hydrogen regions have a partial positive charge (δ+).
Evaporation of sweat in mammals or evaporation of water from the leaves of plants...
removes excess heat and prevents terrestrial organisms from overheating.
Occasionally, a hydrogen atom participating in a hydrogen bond between two water molecules...
shifts from one molecule to the other. The hydrogen atom leaves its electron behind and is transferred as a single proton—a hydrogen ion (H+). The water molecule that lost the proton is now a hydroxide ion (OH−). The water molecule with the extra proton is now a hydronium ion (H3O+).
Adding an acid to a solution...
shifts the balance between H+ and OH− toward H+ and leads to a decrease in the OH− concentration.
A liquid that is a completely homogeneous mixture of two or more substances is called a...
solution. A sugar cube in a glass of water eventually dissolves to form a uniform solution of sugar and water.
Even in a low-temperature liquid (with low average kinetic energy)...
some molecules move fast enough to evaporate.
As ice starts to melt...
some of the hydrogen bonds break, and water molecules can slip closer together than they can while in the ice state.
The advantage of using a mole as a unit of measure is...
that a mole of one substance has the same number of molecules as a mole of any other substance. If substance A has a molecular weight of 10 daltons and substance B has a molecular weight of 100 daltons, then we know that 10 g of substance A has the same number of molecules as 100 g of substance B. A mole of sucrose contains 6.02 × 1023 molecules and weighs 342 g, while a mole of ethyl alcohol (C2H6O) also contains 6.02 × 1023 molecules but weighs only 46 g because the molecules are smaller.
The chemical processes in the cell can be disrupted by changes in...
the H+ and OH− concentrations away from their normal values, usually near pH 7. The pH of human blood is close to 7.4. A person cannot survive for more than a few minutes if the blood pH drops to 7 or rises to 7.8.
Although there are several ways to measure heat energy, one convenient unit is the calorie (cal). One calorie is...
the amount of heat energy necessary to raise the temperature of 1 gram of water by 1°C. A calorie is released when 1 g of water cools by 1°C.
In many biological processes, the kilocalorie (kcal) is a more convenient unit. One kilocalorie is...
the amount of heat energy necessary to raise the temperature of 1000 g (1 kg) of water by 1°C.
The specific heat of a substance is...
the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C.
The speed of molecular movement varies; temperature is...
the average kinetic energy of molecules.
Adhesion
the clinging of one substance another, also contributes, as water adheres to the walls of the vessels.
Temperature measures...
the intensity of heat in a body of matter due to the average kinetic energy of molecules. As the average speed of molecules increases, a thermometer records an increase in temperature.
The pH of a solution is defined as...
the negative logarithm (base10) of the hydrogen ion concentration. pH=−log[H+]
When carrying out experiments, we use mass to calculate...
the number of molecules.
If any life-forms are found, their study will shed light on...
the process of evolution from an entirely new perspective.
Heat of vaporization is...
the quantity of heat that a liquid must absorb for 1 g of it to be converted from liquid to gas.
The substance that is dissolved is...
the solute.
Some hydrophilic substances do not dissolve because...
their molecules are too large. For example, cotton is hydrophilic because cellulose, its major constituent, has numerous polar covalent bonds. However, its giant cellulose molecules are too large to dissolve in water. Water molecules form hydrogen bonds with the cellulose fibers of cotton. When you dry yourself with a cotton towel, the water is pulled into the towel.
Polar molecules are soluble in water because...
they form hydrogen bonds with water.
Acidification of rivers, lakes, seas, and rain...
threatens the environment.
When water is in its liquid form, its hydrogen bonds are....
very fragile, about one-twentieth as strong as covalent bonds. Hydrogen bonds form, break, and re-form with great frequency. Each hydrogen bond lasts only a few trillionths of a second, but the molecules continuously form new hydrogen bonds with a succession of partners. At any given instant, a substantial percentage of all water molecules are hydrogen-bonded to their neighbors.
Although the dissociation of water is reversible and statistically rare, it is...
very important in the chemistry of life.
Mars, like Earth, has an ice cap at both poles. In 2015, scientists found ...
vidence of water flowing on Mars, and other studies suggested conditions existed that coils have supported microorganismal life. Drilling below the surface may be the next step in the search for signs of life on Mars.
In an aqueous solution...
water is the solvent.
Water is also unusual in that the solid state...
(ice) floats on the liquid state (water). This rare and important property emerges from the chemistry of water.
In a neutral solution...
[H+] = 10−7 M and pH = 7.
solutions with more H+ than OH- are...
acidic
A substance that has an affinity for water is...
hydrophilic (water-loving).
The pH decreases as...
the H+ concentration increases.
Heating a liquid increases...
the average kinetic energy and increases the rate of evaporation.
The dissolving agent is...
the solvent.
Because water is essential to life on Earth, astrobiologists...
(biologists who look for life elsewhere in the universe) seeking extraterrestrial life have concentrated on planets that may have water.
Based on measurements of CO2 levels in air bubbles trapped in ice over thousands of years, scientists calculate that the pH of the oceans is...
0.1 pH units lower now than any time in the past 420,000 years.
Another common energy unit, the joule (J), is equivalent to...
0.239 cal.
By definition, the specific heat of water is...
1 cal per gram per degree Celsius, or 1 cal/g/°C.
A one-molar (1 M) solution has...
1 mole of a substance dissolved in 1 liter of a solvent, typically water.
Ice is about ______ less dense than water at 4°C. Therefore, ice floats on the cool water below.
10%
At equilibrium, the concentration of H+ or OH− is...
10⁻⁷M (at 25°C). There is only one ten-millionth of a mole of hydrogen ions per liter of pure water and an equal number of hydroxide ions.
However, the human stomach has strongly acidic digestive juice with a pH of about...
2.
In pure water, only one water molecule in every ______ is dissociated.
554 million
Most biological fluids have pH values in the range...
6-8.
Because of the way in which Avogadro's number and the unit dalton were originally defined, there are ______ daltons in 1 g.
6.02 x 1023
Water's high specific heat affects Earth as a whole as well as individual organisms.
A large body of water can absorb a large amount of heat from the sun during the daytime in the summer and yet warm only a few degrees. At night and during the winter, the warm water heats the cooler air. Therefore, the oceans and coastal land areas have more stable temperatures than inland areas.
Decreasing pH may alter the delicate balance of conditions for life on Earth.
About 25% of human-generated CO2 is absorbed by the oceans. In spite of the huge volume of water in the oceans, scientists worry that this absorption of so much CO2 will harm marine life and ecosystems. And recent data have shown that such fears are well founded. When CO2 dissolves in seawater, it can react with water (H2O) to form carbonic acid (H2CO3).
The actual number of molecules in a mole is called...
Avogadro's number, 6.02×10²³.
The Molecule That Supports All of Life
Because water is the substance that makes life possible on Earth, astronomers hope to find evidence of water on newly discovered planets orbiting distant stars. Water is the substance that makes life on Earth possible. All organisms are made mostly of water and live in an environment dominated by water.
Cohesion of Water Molecules
Collectively, hydrogen bonds hold water together, a phenomenon called cohesion. Cohesion among water molecules plays a key role in transporting water and dissolved nutrients against gravity in plants. Water molecules move up from the roots to the leaves of a plant through water-conducting vessels. As water molecules evaporate from a leaf, other water molecules from vessels in the leaf replace them. Hydrogen bonds cause water molecules leaving the vessels to tug on molecules farther down. This upward pull is transmitted down to the roots.
Carbonic acid is a weak acid, which reversibly releases and accepts hydrogen ions.
H2CO3 (Carbonic acid) ⇔ HCO3- (Bicarbonate ion) +H+ (Hydrogen ion) Only 1% of its molecules are dissociated at any particular time. Still, that is enough to shift the balance of H+ and OH- from neutrality.
Heat and temperature are related but not identical.
Heat depends in part on the matter's volume, while temperature is the average kinetic energy of molecules, regardless of volume. When two objects of different temperatures come together, heat passes from the warmer object to the cooler object until the two are the same temperature. Molecules in the cooler object speed up at the expense of the kinetic energy of the warmer object. Ice cubes cool a glass of soda by absorbing heat from the soda as the ice melts.
HCl and NaOH dissociate completely when mixed with water.
Hydrochloric acid is a strong acid, and sodium hydroxide is a strong base.
Ice floating on water has important consequences for life.
If ice sank, eventually all ponds, lakes, and even oceans would freeze solid. During the summer, only the upper few centimeters of oceans would thaw. Instead, the surface layer of ice insulates the liquid water below, preventing it from freezing and allowing life to exist under the frozen surface. Ice also provides solid habitat for Arctic animals like polar bears and seals.
The pH Scale
In any aqueous solution at 25°C, the product of the H+ and OH- concentrations is constant at 10-14. Brackets ([H+] and [OH−]) indicate the molar concentration of the enclosed substance. [H+][OH−]=10-14
Global warming is affecting icy environments around the globe.
In northern Alaska and Canada, the average air temperature has risen 2.2°C since 1961. As a result, ice forms later, melts earlier, and covers a smaller area of the Arctic, threatening animals that depend on ice for survival.
Water's high heat of vaporization moderates climate.
Much of the sun's heat absorbed by tropical oceans is used for the evaporation of surface water. As moist tropical air moves to the poles, water vapor condenses to form rain, releasing heat.
Human activities threaten water quality.
The burning of fossil fuels releases gaseous compounds into the atmosphere, which react with water to increase the acidity of the water.
In contrast, ammonia is a relatively weak base.
The double arrows in the reaction for ammonia indicate that the binding and release of hydrogen ions are reversible reactions. At equilibrium, there is a fixed ratio of NH4+ to NH3.
As a liquid evaporates, the surface of the liquid that remains behind cools, a phenomenon called evaporative cooling.
The most energetic molecules are the most likely to evaporate, leaving the lower-kinetic energy molecules behind. It is as if the fastest 100 runners at a college transferred to another school; the average speed of the remaining students would decline.
Although the pH scale is based on [H+], values for [OH−] can be easily calculated from the product relationship.
The pH of a neutral solution is 7.Acidic solutions have pH values less than 7, and basic solutions have pH values greater than 7.
To express this variation more conveniently, the H+ and OH− concentrations are typically expressed with the pH scale.
The pH scale, ranging from 1 tom14, compresses the range of concentrations by employing logarithms.
Evaporative Cooling
The transformation of a molecule from a liquid to a gas is called vaporization, or evaporation.
Floating of Ice on Liquid Water
Water is unusual because it is less dense as a solid than as a cold liquid. Most materials contract as they solidify, but water expands.
Temperature and Heat
Water moderates air temperatures by absorbing heat from warmer air and releasing the stored heat to cooler air.
Water's High Specific Heat
Water stabilizes temperature because it has a high specific heat.
How would we make a liter (L) of solution consisting of 1 mol of sucrose dissolved in water?
We would slowly add water to 342 g (1 mol) of sucrose until the total volume was 1 liter and all the sugar was dissolved.
In a neutral solution at room temperature...
[H+] = 10-7 M and [OH−] = 10-7 M.
Any substance that reduces the hydrogen ion concentration in a solution is...
a base.
Surface tension
a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion. Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface. Water behaves as if covered by an invisible film. Some animals can stand, walk, or run on water without breaking the surface.
Heat is...
a measure of the total quantity of kinetic energy due to molecular motion in a body of matter.
