[Chapter 2] Chemistry Comes Alive

Question 1

[2.1] Matter is the stuff of the universe and energy moves matter

Matter: Definition/States of Matter

Answer 1

Matter is anything that occupies space and has mass.

Matter exists in solid, liquid, and gaseous states.

Question 2

[2.1] Matter is the stuff of the universe and energy moves matter

Energy: Definition

Answer 2

Energy is defined as the capacity to do work, or to put matter into motion.

The greater the work done, the more energy is used doing it.

Question 3

[2.1] Matter is the stuff of the universe and energy moves matter

Energy: Kinetic vs Potential

Answer 3

Energy exists in two states, and each can be tranformed to the other

• Kinetic energy is energy in action.
• Potential energy is stored energy (inactive energy that has the potential, or capability, to do work but is not presently doing so)

Question 4

[2.1] Matter is the stuff of the universe and energy moves matter

Forms of Energy: Chemical

Answer 4

Chemical energy is the form stored in the bonds of chemical substances

When chemical reactions occur that rearrange the atoms of the chemicals in a certain way, the potential energy is unleashed and becomes kinetic energy, or energy in action

Example: chemical energy in the form of ATP

Question 5

[2.1] Matter is the stuff of the universe and energy moves matter

Forms of Energy: Electrical

Answer 5

Electrical energy results from the movement of charged particles

Examples:

• Electrical currents are generated when charged particles called ions move along or across cell membranes
• The nervous system uses electrical currents, called nerve impulses, to transmit messages from one part of the body to another
• Electrical currents traveling across the heart stimulate it to contract (beat) and pump blood

Question 6

[2.1] Matter is the stuff of the universe and energy moves matter

Forms of Energy: Mechanical

Answer 6

Mechanical energy is energy directly involved in moving matter

Example: when you ride a bicycle, your legs provide the mechanical energy that moves the pedals

Question 7

[2.1] Matter is the stuff of the universe and energy moves matter

Forms of Energy: Radiant or Electromagnetic Radiation

Answer 7

Radiant energy, or electromagnetic radiation, is energy that travels in waves

These waves, which vary in length, are collectively called the electromagnetic spectrum

They include:

• Visible light
• Infrared waves
• Radio waves
• Ultraviolet rays (cause sunburn, but also stimulate your body to make vitamin D)
• X rays

Question 8

[2.1] Matter is the stuff of the universe and energy moves matter

Energy: Form Conversions

Answer 8

With few exceptions, energy is easily converted from one form to another. For example, the chemical energy (in gasoline) that powers the motor of a speedboat is converted into the mechanical energy of the whirling propeller that makes the boat skim across the water

Energy conversions are quite inefficient. Some of the initial energy supply is always “lost” to the environment as heat. It is not reallly lost because energy cannot be created or destroyed, but that portion given off as heat is at least partly unusable. Example: lightbulb.

All energy conversions in the body liberate heat. This heat helps to maintain our relatively high body temperature, which influences body functioning.

Question 9

[2.2] The properties of an element depend on the structure of its atoms

General

Answer 9

All matter is composed of elements, unique substances that cannot be broken down into simpler substances by ordinary chemical methods.

Four elements - carbon, oxygen, hydrogen, and nitrogen - make up about 96% of body weight

Each element is composed of more or less identical particles called atoms

Every element’s atoms differ from those of all other elements and give the element its unique physical [those we can detect with our senses (such as color and texture) or measure (such as boiling point and freezing point)] and chemical properties [which pertain to the way atoms interact with other atoms (bonding behavior)]

Question 10

[2.2] The properties of an element depend on the structure of its atoms

Structure of Atoms

Answer 10

Atoms are clusters of smaller particles called protons, neutrons, and electrons

The old idea of atomic indivisibility is useful because an atom loses the unique properties of its element when it is split into its subatomic particles

An atom’s subatomic particles differ in mass, electrical charge, and position in the atom

An atom has a central nucleus containing protons and neutrons tightly bound together

Protons bare a positive electrical charge, and neutrons are neutral, so the nucleus is positively charged overall

Protons and neutrons are heavy particles and have approximately the same mass, arbitrarily designated as 1 atomic mass unit (1 amu). Thus the nucleus accounts for nearly the entire mass of the atom (99.9%)

The tiny electrons bear a negative charge equal in strength to the positive charge of the proton. The mass of an electron is usually designated as 0 amu.

All atoms are electrically neutral because the number of protons in an atom is precisely balanced by its number of electrons. For any atom, the number of protons and electrons is always equal

Orbitals are regions around the nucleus in which a given electron or electron pair is likely to be found most of the time

Most of the volume of an atomo is empty space, and nearly all of its mass is concentrated in the central nucleus

Question 11

#9

[2.2] The properties of an element depend on the structure of its atoms

Identifying Elements

Answer 11

All protons are alike, regardless of the atom considered. However, atoms of different elements are composed of different numbers of protons, neutrons, and electrons

The simplest and smallest atom, hydrogen, has 1 proton, 1 electron, and no neutrons.

All we need to know about a particular element are its atomic number, mass number, and atomic weight.

• A = Mass number (# of protons + # of neutrons)
• Z = Atomic Number (# of protons and electrons)
• N = Neutron Number

Mass Number = Z + N

Number of Neutrons = A - Z

Question 12

[2.2] The properties of an element depend on the structure of its atoms

Identifying Elements: Atomic Number

Answer 12

The atomic number of any atom is equal to the number of protons in its nucleus and is written as a subscript to the left of its atomic symbol

The number of protons is always equal to the number of electrons in an atom, so the atomic number indirectly tells us the number of electrons in the atom as well

Electrons determine the chemical behavior of atoms

Question 13

[2.2] The properties of an element depend on the structure of its atoms

Identifying Elements: Mass Number

Answer 13

The mass number of an atom is the sum of the masses of its protons and neutrons. The mass of the electrons is so small that it is ignored.

Recall that protons and neutrons have a mass number of 1 amu

Hydrogen has only one proton in its nucleus, so its atomic and mass numbers are the same: 1

The mass number is usually indicated by a superscript to the left of the atomic symbol

Question 14

[2.2] The properties of an element depend on the structure of its atoms

Identifying Elements: Isotopes

Answer 14

Nearly all known elements have two or more structural variations called isotopes which have the same number of protons (and electrons), but differ in the number of neutrons they contain

Isotopes can also be written with the mass number following the symbol (example: C-14)

Question 15

[2.2] The properties of an element depend on the structure of its atoms

Identifying Elements: Atomic Weight

Answer 15

Atomic weight is an average of the relative weights (mass numbers) of all the isotopes of an element, taking into account their relative abundance in nature

As a rule, the atomic weight of an element is approximately equal to the mass number of its most abundant isotope

Question 16

[2.2] The properties of an element depend on the structure of its atoms

Radioisotopes: Definition

Answer 16

The heavier isotopes of many elements are unstable, and their atoms decompose spontaneously into more stable forms

This process of atomic decay is called radioactivity, and isotopes that exhibit this behavior are called radioisotopes

Question 17

[2.2] The properties of an element depend on the structure of its atoms

Radioisotopes: Explanation

Answer 17

The disintegration of a radioactive nucleus may be compared to a tiny explosion. It occurs when subatomic alpha, beta, or gamma particles/rays are ejected from the atomic nucleus

Why does this happen? The important point to note is that the dense nuclear particles are composed of even smaller particles called quarks that associate in one way to form protons and in another way to form neutrons. Apparently, the “glue” that holds these nuclear particles together is weaker in the heavier isotopes

Question 18

[2.2] The properties of an element depend on the structure of its atoms

Radioisotopes: Uses

Answer 18

Because we can detect radioactivity with scanners, and radioactive isotopes share the same chemistry as their more stable isotopes, radioisotopes are valuable tools for biological research and medicine

Most radioisotopes used in the clinical setting are used for diagnoses, that is, to localize and illuminate damaged or cancerous tissues.

• For example, iodine-131 is used to determine the size and activity of the thyroid gland and to detect thyroid cancer
• PET scans use radioisotopes to probe the workings of molecules deep within our bodies
• Radium-226, cobalt-60, and certain other radioisotopes that decay by gamma emission are used to destroy localized cancer cells

All radioisotopes, regardless of the purpose for which they are used, damage living tissue, and they all gradually lose their radioactive behavior

The time required for a radioisotope to lose one-half of its activity is called its half-life

Question 19

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Molecules and Compounds: Definitions

Answer 19

A combination of two or more atoms held together by chemical bonds is called a molecule. If two or more molecules of the same element combind, the resulting substance is called a molecules of that element.

When two or more different kinds of atoms bind, they form molecules of a compound.

Question 20

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Molecules and Compounds: Molecules of Compounds

Answer 20

Compounds are chemically pure, and all of their molecules are identical

A molecule is the smallest particle of a compound that still has the specific characteristics of the compound

The properties of compounds are usually very different from those of the atoms they contain

Question 21

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures

Answer 21

Mixtures are substances composed of two or more components physically intermixed.

Three basic types:

• Solutions
• Colloids
• Suspensions

Question 22

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures: Solutions (Definition)

Answer 22

Solutions are homogeneous mixtures of componenets that may be gases, liquids, or solids.

Question 23

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures: Solutions (Homogeneous)

Answer 23

Homogeneous means that the mixture has exactly the same composition or makeup throughout - a sample taken from any part of the mixture has the same composition (in terms of the atoms or molecules it contains) as a sample taken from any other part of the mixture.​

Question 24

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures: Solutions (Solvent and Solute)

Answer 24

The substance present in the greatest amount is called the solvent (or dissolved medium). Solvents are usually liquids.

Substances present in smaller amounts (dissolved in the solvent) are called solutes.

Question 25

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures: Solutions (True Solutions)

Answer 25

Water is the body’s chief solvent. Most solutions in the body are true solutions containing gases, liquids, or solids dissolved in water.

Examples of true solutions:

• saline solution [table salt (NaCl) and water]
• a mixture of glucose and water
• mineral water

The solutes of true solutions are minute, usually in the form of individual atoms and molecules. Consequently, they are not visible to the naked eye, do not settle out, and do not scatter light.

Question 26

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures: Solutions (Concentrations in Percent)

We describe true solutions in terms of their concentration, which may be indicated in various ways.

Answer 26

Solutions in lab are often described in terms of the percent (parts per 100 parts) of the solute in the total solution. This designation always refers to the solute percentage, and unless otherwise noted, water is assumed to be the solvent.

Question 27

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures: Solutions (Concentrations in Molarity)

We describe true solutions in terms of their concentration, which may be indicated in various ways.

Answer 27

Another way to express the concentraion of a solution is in terms of its molarity, or moles per liter, indicated by M.

A mole of any element or compound is equal to its atomic weight or molecular weight (sum of the atomic weights) in grams.

Example: Glucose is C₆H₁₂O₆, to compute the molecular weight of glucose, you would look up the atomic weight of each of its atoms in the periodic table and compute its molecular weight as follows:

C (6 x 12.011) = 72.066

H (12 x 1.008) = 12.096

O (6 x 15.999) = 95.994

Sum is = 180.156

Then, to make a one-molar solution of glucose, you would weigh out 180.156 grams (g) called a gram molecular weight, of glucose and add enough water to make 1 liter (L) of solution.

In short, a one-molar solution (abbreviated 1.0M) of a chemical substance is one gram molecular weight of the substance (or one gram atomic weight in the case of elemental substacnes) in 1 L (1000 milliliters) of solution.

The beauty of using the mole as the basis of preparing solutions is its precision. One mole of any substance always contains exactly the same number of solute particles, that is, 6.02 x 10²³. This number is called Avogadro’s number.

Question 28

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures: Colloids

Answer 28

Colloids, also called emulsions, are heterogeneous mixtures, which means that their composition is dissimilar in different areas of the mixture.

The solute particles do not settle out. They scatter light.

Some colloids have the ability to undergo sol-gel transformations, to change reversibly from a fluid (sol) to a more solid (gel) state.

Examples:

• Jello
• Cytosol, the semifluid material in living cells

Question 29

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Mixtures: Suspensions

Answer 29

Suspensions are heterogenous mixtures with large, often visible solutes that tend to settle out.

Examples:

• A mixture of sand and water
• Blood

Question 30

[2.3] Atoms bound together form molecules; different molecules can make mixtures

Distinguishing Mixtures from Compounds

Answer 30

Mixtures differ from compounds in several important ways:

• No chemical bonding occurs between the components of a mixture. The properties of atoms and molecules are not changed when they become part of a mixture. They are only physically intermixed.
• Depending on the mixture, its components can be separated by physical means - straining, filtering, evaporation, and so on. Compounds, by contrast, can be separated into their constituent atoms only by chemical means (breaking bonds).
• Some mixtures are homogenous, whereas others are heterogeneous. All compounds are homogeneous.

Question 31

[2.4] The three types of chemical bonds are ionic, covalent, and hydrogen

Definition of Chemical Bond

Answer 31

A chemical bond is an energy relationship between the electrons of the reacting atoms.

Question 32

[2.4] The three types of chemical bonds are ionic, covalent, and hydrogen

The Role of Electrons in Chemical Bonding: Electron Shells/Orbitals

Answer 32

Electrons occupy regions of space called electron shells that consecutively surround the atomic nucleus.

Each electron shell contains one or more orbitals. Recall that orbitals are regions around the nucleus in which a given electron is likely to be found most of the time.

Question 33

[2.4] The three types of chemical bonds are ionic, covalent, and hydrogen

The Role of Electrons in Chemical Bonding: Electron Energy Level

Answer 33

Each electron shell represents a different energy level. Each electron is a particle with a certain amount of potential energy. The terms electron shell and energy level are used interchangeably.

The attraction between the positively charged nucleus and negatively charged electrons is greatest when electrons are closest to the nucleus and falls off with increasing distance.

This statement explains why electrons farthest from the nucleus

1. have the greatest potential energy (it takes more energy for them to overcome the nuclear attraction and reach the more distant energy levels)
2. are most likely to interact chemically with other atoms (they are the least tightly held by their own nucleus and the most easily influenced by other atoms and molecules)

Question 34

[2.4] The three types of chemical bonds are ionic, covalent, and hydrogen

Types of Chemical Bonds: Ions (Definitions)

Answer 34

Electrons can be transferred from one atom to another, and when this happens, the precise balance of + and - charges is lost so that charged particles called ions are formed

An ionic bond is a chemical bond between atoms formed by the transfer of one or more elctrons from one atom to the other

• the atom that gains one or more electrons is the electron acceptor. It acquires a net negative charge and is called an anion
• the atom that loses electrons is the electron donor. It acquires a net positive charge and is called an anion.

Because opposite charges attract, these ions tend to stay close together, resulting in an ionic bond

Ionic bonds are commonly formed between atoms with 1 or 2 valence shell electrons (the metallic elements, such as Na, Ca, and K) and atoms with 7 valence shell electrons (such as Cl, F, and I).

Question 35

[2.4] The three types of chemical bonds are ionic, covalent, and hydrogen

Types of Chemical Bonds: Ions (Salts)

Answer 35

Most ionic compounds fall in the chemical category called salts.

In the dry state, salts such as sodium chloride do not exist as individual molecules. Instead, they form crystals, large arrays of cations and anions held together by ionic bonds.

Question 36

[2.4] The three types of chemical bonds are ionic, covalent, and hydrogen

Types of Chemical Bonds: Covalent Bonds (General)

Answer 36

The shared electrons orbit and “belong to” the whole molecule, ensuring the stability of each atom.

Single, double, and triple bonds exist.

• In general, small atoms with 6 or 7 valence shell electrons are electron-hungry and attract electrons very strongly, a capability called electronegativity
• On the other hand, most atoms with only one or two valence shell electrons tend to be electropositive

Question 37

[2.4] The three types of chemical bonds are ionic, covalent, and hydrogen

Types of Chemical Bonds: Covalent Bonds (Polarity)

Answer 37

Nonpolar molecules are electrically balanced because they do no have separate + and - poles of charge (the electrons are shared equally between the atoms of the molecule for the most part)

A molecule’s shape helps determine what other molecules or atoms it can interact with. It may also result in unequal electron pair sharing, creating a polar molecule, especially in nonsymmetrical molecules containing atoms with different electron-attracting abilities

Example: Water

Because electrons are negatively charged, the oxygen end of the molecule is slightly more negative (the cahrge is indicated with a delta and a minus as δ^-) and the hydrogen end slightly more positive (indicated by δ⁺).

Because water has two poles of charge, it is a polar molecule, or dipole.

Question 38

[2.4] The three types of chemical bonds are ionic, covalent, and hydrogen

Types of Chemical Bonds: Hydrogen Bonds

Answer 38

Hydrogen bonds form when a hydrogen atom, already covalently linked to one electronegative atom (usually nitrogen or oxygen), is attracted by another electron-hungry atom, so that a “bridge” forms between them.

Hydrogen bonding is common between dipoles such as water molecules because the slightly negative oxygen atoms of one molecule attract the slightly positive hydrogen atoms of other molecules.

Hydrogen bonding is responsible for the tendency of water molecules to cling together and form films, referred to as surface tension.

Although hydrogen bonds are too weak to bind atoms together to form molecules, they are important intramolecular bonds (literally, bonds within molecules), which hold parts of a single large molecule in a specific three-dimensional shape.

Question 39

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Chemical Equations

Answer 39

We can write chemical reactions in symbolic form as chemical equations

In equations, a number written as a subscript indicates that the atoms are joined by chemical bonds. A number written as a prefix denotes the number of unjoined atoms or molecules.

A chemical equation contains the following information:

• The reactants: the number and kinds of interacting substances
• The products: the chemical composition of the result of the reaction
• The relative proportions: balanced equations indicate the relative proportion of each reactant and product

The equation may be read in terms of molecules or moles. Using moles is more practical because it is impossible to measure out one atom or one molecule of anything!

Question 40

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Types of Chemical Reactions

Answer 40

Synthesis reactions are the basis of constructive, or anabolic, activities.

A decomposition reaction occurs when a moleceule is broken down into smaller molecules or its constituent atoms. Decomposition reactions underlie all degradative, or catabolic, processes in body cells.

Exchange, or displacement, reactions involve both synthesis and decomposition. Bonds aer both made and broken.

Question 41

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Types of Chemical Reactions: Oxidation-Reduction Reactions

Answer 41

Oxidation-reduction reactions are called redox reactions for short.

They are the basis of all reactions in which food fuels are broken down for energy (that is, in which ATP is produced).

They are also a special type of exchange reaction because electrons are exchanged between the reactants.

The reactant losing the electrons is the electron donor and is said to be oxidized. The reactant taking up the transferred electrons is the electron acceptor and is said to become reduced.

Redox reactions also occur when ionic compounds are formed; Ex. NaCl. However, not all oxidation-reduction reactions involve complete transfer of electrons - some simply change the pattern of electron sharing in covalent bonds.

Example: oxidation-reduction reaction of glucose: Glucose is oxidized to carbon dioxide as it loses hydrogen atoms, and oxygen is reduced to water as it accepts the hydrogen atoms.

Question 42

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Energy Flow in Chemical Reactions

Answer 42

Because all chemical bonds represent stored chemical energy, all chemical reactions ultimately result in net absorptionor release of energy.

Reactions that release energy are exergonic reactions. These reactions yield products with less energy than the initial reactants, along with energy that can be harvested for other uses. With a few exceptions, catabolic and oxidative reactions are exergonic.

The products of energy-absorbing, or endergonic, reactions contain more potential energy in their chemical bonds than did the reactants. Anabolic reactions are typically endergonic reactions.

Question 43

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Reversibility of Chemical Reactions

Answer 43

All chemical reactions are theoretically reversible.

Reversibility is indicated by a double arrow. When the arrows differ in length, the longer arrow indicates the major direction in which the reaction proceeds.

When the arrows are of equal length, neither the forward reaction nor the reverse reaction is dominant. Such a chemical reaction is said to be in a state of chemical equilibrium. Once chemical equilibrium is reached, there is no further net change in the amounts of reactants and products unless more of either are added to the mix. Product molecules are still formed and broken down, but the balance established when equilibrium was reached (such as greater numbers of product molecules) remains unchanged.

All chemical reactions are reversible, but many biological reactions show so little tendency to go in the reverse direction that they are irreversible for all practical purposes.

Chemical reactions that release energy will not go in the opposite direction unless energy is put back into the system. Furthermore, if a product of a reaction is continuously removed from the reaction site, it is unavailable to take part in the reverse reaction.

Question 44

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Factors Influencing Rate of Chemical Reactions

Answer 44

For atoms and molecules to react chemically in the first place, they must collide with enough force to overcome the repulsion between their electrons.

Question 45

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Factors Influencing Rate of Chemical Reactions: Temperature

Answer 45

Temperature: increasing the temperature of a substance increases the kinetic energy of its particles and the force of their collisions. For this reason, chemical reactions proceed more quickly at higher temperatures.

Question 46

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Factors Influencing Rate of Chemical Reactions: Concentration

Answer 46

Concentration: chemical reactions progress most rapidly when the reacting particles are present in high numbers, because the chance of successful collisions is greater.

As the concentration of the reactants declines, the reaction slows. Chemical equilibrium eventually occurs unless additional reactants are added or products are removed from the reaction site.

Question 47

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Factors Influencing Rate of Chemical Reactions: Particle Size

Answer 47

Particle size: smaller particles move faster than larger ones (at the same temperature) and tend to collide more frequently and more forcefully.

Hence, the smaller the reacting particles, the faster a chemical reaction goes at a given temperature and concentration.

Question 48

[2.5] Chemical reacitons occur when electrons are shared, gained, or lost

Factors Influencing Rate of Chemical Reactions: Catalysts

Answer 48

Catalysts: are substances that increase the rate of chemical reactions without themselves becoming chemically changed or part of the product.

Biological catalysts are called enzymes.

Question 49

[2.6] Inorganic compounds include water, salts, and many acids and bases

Water

Answer 49

Water makes up to 60-80% of the volume of most living cells.

Question 50

[2.6] Inorganic compounds include water, salts, and many acids and bases

Water: High Heat Capacity

Answer 50

High heat capacity: wter has a high heat capacity. In other words, it absorbs and releases large amounts of heat before changing appreciably in temperature itself.

This property of water prevents sudden changes in temperature caused by external factors, such as sun or wind exposure, or by internal conditions that release heat rapidly, such as vigorous muscle activity. As part of blood, water redistributes heat among body tissues, ensuring temperature homeostasis.

Question 51

[2.6] Inorganic compounds include water, salts, and many acids and bases

Water: High Heat of Vaporization

Answer 51

High heat of vaporization: when water evaporates, or vaporizes, it changes from a liquid to a gas (water vapor). This transformation requires that large amounts of heat be absorbed to break the hydrogen bonds that hold water molecules together.

This property is extremely beneficial when we sweat. As perspiration (mostly water) evaporates from our skin, large amounts of heat are removed from the body, providing efficient cooling.

Question 52

[2.6] Inorganic compounds include water, salts, and many acids and bases

Water: Polar Solvent Properties

Answer 52

Polar solvent properties:

Water is often called the universal solvent.

Biological molecules do not react chemically unless they are in solution, and virtually all chemical reactions occurring in the body depend on water’s solvent properties.

Because water molecules are polar, they orient themselves with their slightly negative ends toward the positive ends of the solutes, and vice versa, first attracting the solute molecules, and then surrounding them. This polarity of water explains why ionic compounds and other small reactive molecules (such as acids and bases) dissociate in water, their ions separating from each other and becoming evenly scattered in the water, forming true solutions.

Water also forms layers of water molecules, called hydration layers, around large charged molecules such as proteins, shielding them from the effects of other charged substances in the civinity and preventing them from settling out of solution. Such protein-water mixtures are biological colloids.

Water is the body’s major transport medium because it is such an excellent solvent.

Question 53

[2.6] Inorganic compounds include water, salts, and many acids and bases

Water: Reactivity

Answer 53

Reactivity: water is an important reactant in many chemical reactions. Example: hydrolysis reactions.

Question 54

[2.6] Inorganic compounds include water, salts, and many acids and bases

Water: Cushioning

Answer 54

Cushioning: by forming a resilient cushion around certain body organs, water helps protect them from physical trauma.

Question 55

[2.6] Inorganic compounds include water, salts, and many acids and bases

Salts

Answer 55

A salt is an ionic compound containing cations other than H⁺ and anions other than the hydroxyl ion (OH^-).

When salts are dissolved in water, they dissociate into their component ions.

All ions are electrolytes, substances that conduct an electrical current in solution.

Note that groups of atoms that bear an overall charge are called polyatomic ions.

Salts commonly found in the body include NaCl, CaCO₃ (calcium carbonate), and KCl (potassium chloride).

Question 56

[2.6] Inorganic compounds include water, salts, and many acids and bases

Acids and Bases

Answer 56

Like salts, acids and bases are electrolytes. They ionize and dissociate in water and can then conduct an electrical current.

Question 57

[2.6] Inorganic compounds include water, salts, and many acids and bases

Acids and Bases: Acids

Answer 57

Acids have a sour taste, can react with (dissolve) many metals.

An acid is a substance that releases hydrogen ions (H⁺) in detectable amounts. Because a hydrogen ion is just a hydrogen nucleus, or “naked” proton, acids are also defined as proton donors.

When acids dissolve in water, they release hydrogen ions (protons) and anions. It is the concentration of protons that determines the acidity of a solution. The anions have little or no effect on acidity.

Question 58

[2.6] Inorganic compounds include water, salts, and many acids and bases

Acids and Bases: Bases

Answer 58

Bases have a bitter taste, feel slippery

Bases are proton acceptors - that is, they take up hydrogen ions (H⁺) in detectable amounts.

Common bases include the hydroxides. Like acids, hydroxides dissociate when dissolved in water, but in this case hydroxyl ions (OH^-) and cations are liberated.

Common bases in the body:

• Bicarbonate ion (HCO₃^-) (abundant in blood)
• Ammonia (NH₃) (waste product)

Question 59

[2.6] Inorganic compounds include water, salts, and many acids and bases

Acids and Bases: pH: Acid-Base Concentration

Answer 59

The more hydrogen ions in a solution, the more acidic the solution is. Conversely, the greater the concentration of hydroxyl ions (the lower the concentration of H⁺), the more basic, or alkaline, the solution becomes.

The relative concentration of hydrogen ions in various body fluids is measured in concentration units called pH units.

The pH scale that resulted is based on the concentration of hydrogen ions in a solution, expressed in terms of moles per liter, or molarity. The pH scale runs from 0 to 14 and is logarithmic. In other words, each successive change of one pH unit represents a tenfold change in hydrogen ion concentration. The pH of a solution is thus defined as the negative logarithm of the hydrogen ion concentration [H⁺] in moles per liter, or -log[H⁺​].

• At a pH of 7 (at which [H⁺​] is 10^-7 M), the solution is neutral - neither acidic nor basic. The number of hydrogen ions exactly equals the number of hydroxyl ions (pH = pOH). Absolutely pure (distilled) water has a pH of 7.
• Solutions with a pH below 7 are acidic - the hydrogen ions outnumber the hydroxyl ions. The lower the pH, the more acidic the solution. A solution with a pH of 6 has ten times as many hydrogen ions as a solution with a pH of 7.
• Solutions with a pH higher than 7 are alkaline, and the relative concentration of hydrogen ions decreases by a factor of 10 with each higher pH unit.

Question 60

[2.6] Inorganic compounds include water, salts, and many acids and bases

Acids and Bases: Neutralization

Answer 60

When acids and bases are mixed, they react with each other in displacement reactions to form water and a salt.

This type of reaction is called a neutralization reaction, because the joining of H⁺ and OH^- to form water neutralizes the solution. Although the salt produced is written in molecular form (ex. NaCl); remember that it actually exists as dissociated sodium and chloride ions when dissolved in water.

Question 61

[2.6] Inorganic compounds include water, salts, and many acids and bases

Acids and Bases: Buffers

Answer 61

Buffers resist abrupt and large swings in the pH of body fluids by releasing hydrogen ions (acting as acids) when the pH begins to rise and by binding hydrogen ions (acting as bases) when the pH drops.

The acidity of a solution reflects only the free hydrogen ions, not those still bound to anions. Acids that dissociate completely and irreversibly in water are called strong acids, because they can dramatically change the pH of a solution. Acids that do not dissociate completely are called weak acids.

Remember that bases are proton acceptors. Thus, strong bases are those, like hydroxides, that dissociate easily in water and quickly tie up H⁺. A weak base accepts relatively few protons.

Example of a buffer system: carbonic acid-bicarbonate system (refer to page 41)