Chapter 2: Small Molecules and the Chemistry of Life

For each of the following bonds, determine: a) whether the bond is polar or nonpolar; b) if polar, which end is δ−; and c) whether the bond is hydrophilic or hydrophobic. C-H C=O O-P C-C

C—H: nonpolar; hydrophobic C=O: polar; δ- at O; hydrophilic O—P: polar; δ− at O; hydrophilic C—C: nonpolar; hydrophobic

Would you expect the elemental composition of Earth's crust to be the same as that of the human body?

The human body has the same elements as Earth's crust but in very different proportions.

Geckos are lizards that are amazing climbers. A gecko can climb up a glass surface and stick to it with a single toe. Professor Kellar Autumn at Lewis and Clark College and his students and collaborators have shown that each toe of a gecko has millions of micrometer-sized hairs, and that each hair splits into hundreds of 200-nanometer tips that provide intimate contact with a surface. Careful measurements show that a million of these tips could easily support the animal, but it has far more. The toes stick well on hydrophilic and hydrophobic surfaces. Bending the hairs allows the gecko to detach. What kind of noncovalent force is involved in gecko sticking?

This is an example of Van der Waals forces, which act over a short distance and do not involve polarity.

Which six elements provide most of the mass of biological organisms? a) C, O, N, H, P, S b) K, O, N, H, P, C c) C, O, Na, H, P, S d) C, O, N, H, F, Mg e) C, O, N, H, P, Mg

a) C, O, N, H, P, S

What is the molecular formula for a water molecule? a) H2O b) HO2 c) H—O—H d) H3O+ + OH- e) None of the above

a) H2O

Which of the following statements about water is not true? a) It releases a large amount of heat when changing from liquid into vapor. b) Its solid form is less dense than its liquid form. c) It is the most effective solvent for polar molecules. d) It is typically the most abundant substance in a living organism. e) It takes part in some important chemical reactions.

a) It releases a large amount of heat when changing from liquid into vapor.

What type of chemical bond connects the two carbon atoms in the molecule shown? H3C-CH3 a) Nonpolar covalent bond b) Asymmetric bond c) Polar covalent bond d) Hydrogen bond e) Double covalent bond

a) Nonpolar covalent bond

In the periodic table, why are hydrogen, lithium, and sodium in the same column? a) They have the same number of unpaired electrons. b) They have different numbers of protons. c) They have the same number of electrons. d) The periodic table is in alphabetical order. e) They have fully filled electron shells.

a) They have the same number of unpaired electrons.

Consider the following statement: Most biochemical reactions take place in aqueous solutions. a) True, because water is the solvent in an aqueous solution and cells are full of water. b) False, because water is the reactant and cannot also be the aqueous solution. c) True, because water is the reactant in the aqueous solution. d) False, because most biochemical reactions love water. e) False because most biochemical reactions involve enzymes and not water.

a) True, because water is the solvent in an aqueous solution and cells are full of water.

Changes in the physical form of water lead to the release or absorption of heat energy. Which of the following statements is true? a) Water absorbs heat from the environment when changing from liquid to gas. b) Water absorbs heat from the environment when changing from liquid to solid. c) Water releases heat to the environment when changing from liquid to gas. d) Water releases heat to the environment when changing from gas to vapor. e) None of the above

a) Water absorbs heat from the environment when changing from liquid to gas.

Which of the following is false? a) Water is acidic. b) Water is a good solvent. c) Water has a high specific heat capacity. d) Water is ubiquitous in living organisms. e) Water is an important habitat for living organisms.

a) Water is acidic.

If carbon dioxide has a molecular weight of approximately 44, then 0.25 moles of carbon dioxide has a) a molecular weight of 11. b) Avogadro's number of molecules. c) a molecular weight of 22. d) approximately 1.5 × 1024 molecules. e) a molecular weight of 88.

a) a molecular weight of 11.

Sweating is a useful cooling device for humans because water a) absorbs a great deal of heat in changing from its liquid state to its gaseous state. b) ionizes readily. c) can exist in three states at temperatures common on Earth. d) is an outstanding solvent. e) absorbs a great deal of heat in changing from its solid state to its liquid state.

a) absorbs a great deal of heat in changing from its liquid state to its gaseous state.

Biological organisms are made of a) atoms, elements, water, other molecules, and ions. b) atoms, water, and other molecules. c) only the elements C, N, P, K, and S. d) only the elements C, N, O, P, K, and S. e) water, other molecules, and cations.

a) atoms, elements, water, other molecules, and ions.

A(n) _______ is an atom that has gained or lost one or more electrons. A(n) _______ bond is created by a(n) _______ attraction between two _______ atoms. a) ion; ionic; electrical; charged b) anion; cation; charged; negative c) cation; ionic; charged; positive d) anion; ionic; electrical; negative e) ionic; van der Waals; electrostatic; charged

a) ion; ionic; electrical; charged

Hydrocarbons are _______ and _______, whereas salts are _______ and _______. a) nonpolar; hydrophobic; polar; hydrophilic b) nonpolar; hydrophilic; polar; hydrophobic c) polar; hydrophilic; nonpolar; hydrophobic d) polar; hydrophobic; nonpolar; hydrophilic e) None of the above

a) nonpolar; hydrophobic; polar; hydrophilic

In the periodic table, when elements are in the same vertical column, they share a similar a) number of valence electrons. b) atomic mass. c) number of neutrons. d) number of unstable isotopes. e) number of protons.

a) number of valence electrons.

Another term for atomic weight is a) relative atomic mass. b) atomic mass. c) atomic number. d) isotopic mass. e) Both a and d

a) relative atomic mass.

A molecule's three-dimensional shape varies by _______ without changing the bond angles or its stability. a) rotating atoms around a covalent bond b) bending a hydrogen bond c) converting a space-filling model to a ball-and-stick model d) converting a space-filling model to a Bohr model e) rotating atoms around an ionic bond

a) rotating atoms around a covalent bond

The _______ in an aqueous solution is water. a) solvent b) solute c) nonpolar solvent d) ion e) reactant

a) solvent

Van der Waals interactions are most similar to a) weak nonpolar interactions. b) product interactions. c) hydrophilic interactions. d) anion interactions. e) reactant interactions.

a) weak nonpolar interactions.

How many electrons occupy the 2s orbital in an oxygen atom? a) 1 b) 2 c) 4 d) 6 e) 8

b) 2

What is the maximum number of electrons contained in a single p orbital? a) 1 b) 2 c) 4 d) 6 e) 8

b) 2

If a tomato puree mixture has a hydrogen concentration of 1 × 10-4 M, it has a pH of a) 3.5. b) 4.0. c) 4.5. d) 5.0. e) 5.5.

b) 4.0.

Given that Avogadro's number is 6.02 × 1023, how many molecules of KCl are there in 10-13 liter of a 1 M KCl solution? a) 6.02 × 1036 b) 6.02 × 1010 c) 6.02 × 10-10 d) 6.02 × 1013 e) 6.02 × 103

b) 6.02 × 1010

_______ capacity is a term used to describe the ability of a solution to prevent large changes in pH with the addition of a base or acid. a) Heat b) Buffering c) Vaporization d) Cohesive e) Freezing

b) Buffering

What is the significance of Avogadro's number? a) It is the total number of molecules found in the world. b) It is the number of molecules in a mole. c) It is the total number of moles of any molecule found in the world. d) It is the number of molecules in 1 kg of a compound. e) None of the above

b) It is the number of molecules in a mole.

Buffers demonstrate which important chemical principle? a) The law of reversibility b) The law of mass action c) The law of compounds d) The law of thermodynamics e) The law of motion

b) The law of mass action

Consider the following statement: In a chemical reaction, the properties of the products are usually similar to the reactants. a) This is true, because redox reactions don't change the properties. b) This is false, because the chemical properties can be significantly altered when chemical partners change. c) This is false, because energy can't be created or destroyed. d) This is false, because a chemical reaction usually changes the mass of the reactants but not their energy. e) This is true, because chemical properties don't change much when chemical partners change.

b) This is false, because the chemical properties can be significantly altered when chemical partners change.

For a covalent bond to be polar, the two atoms that form the bond must have a) similar electronegativities. b) differing electronegativities. c) differing melting points. d) differing numbers of neutrons. e) differing atomic weights.

b) differing electronegativities.

The atomic number of an element a) equals the number of neutrons in an atom. b) equals the number of protons in an atom. c) equals the number of protons minus the number of neutrons. d) equals the number of neutrons plus the number of protons. e) depends on the isotope.

b) equals the number of protons in an atom.

Propane (CH3—CH2—CH3), is considered a nonpolar molecule because it a) forms hydrogen bonds. b) has more attraction to other propane molecules than water. c) is a gas. d) can undergo a chemical reaction with oxygen. e) has more attraction to water than to other propane molecules.

b) has more attraction to other propane molecules than water.

The term hydrophobic is the opposite of a) hydrochloric. b) hydrophilic. c) anisotropic. d) hygroscopic. e) acidophilic.

b) hydrophilic.

Which of the following statements is false? Water has a) the ability to dissolve polar solutes. b) low specific heat capacity. c) the ability to form ice that floats and can insulate the water below. d) the capacity to form hydrogen bonds. e) a rigid crystalline structure below 0°C.

b) low specific heat capacity.

Covalent bond formation depends on the ability of atoms to _______ other atoms. a) donate protons to b) share one or more pairs of electrons with c) share neutrons with d) receive electrons from e) donate electrons to

b) share one or more pairs of electrons with

The molecular weight of acetic acid is 60. How much acetic acid would you need to prepare 10 ml of a 0.001 M (1.0 mM) solution? a) 0.006 g b) 0.6 mg c) 0.0006 g d) 0.06 mg e) 6.0 g

c) 0.0006 g

What is the molarity of 14.5 g of NaCl in 0.5 L of water? a) 0.125 M b) 0.25 M c) 0.5 M d) 0.75 M e) 1 M

c) 0.5 M

Which of the following molecules can be characterized as a weak acid? a) HCl b) HCO3- c) CH3COOH d) NH3 e) None of the above

c) CH3COOH

Which particles determine how an atom interacts with other atoms? a) Protons b) Bosons c) Electrons d) Nuclei e) Neutrons

c) Electrons

What differentiates a strong acid from a weak acid? a) A weak acid accepts H+ ions. b) Ionization of a weak acid is irreversible, whereas ionization of a strong acid is reversible. c) Ionization of a weak acid in water is incomplete, whereas ionization of a strong acid in water is complete. d) A strong acid is more basic than a weak acid. e) None of the above is correct.

c) Ionization of a weak acid in water is incomplete, whereas ionization of a strong acid in water is complete.

Which of the following statements about covalent bonds is not true? a) A covalent bond is stronger than a hydrogen bond. b) A covalent bond can form between atoms of the same element. c) Only a single covalent bond can form between two atoms. d) A covalent bond results from the sharing of electrons by two atoms. e) A covalent bond can form between atoms of different elements.

c) Only a single covalent bond can form between two atoms.

Why is the pH of a 0.1 M solution of acetic acid in water higher than that of a 0.1 M solution of HCl in water? a) HCl is a weaker acid than acetic acid. b) HCl does not fully ionize in water, whereas acetic acid does. c) The acetic acid does not fully ionize in water, whereas HCl does. d) Acetic acid is a better buffer than HCl. e) Acetate (ionized acetic acid) is a strong base.

c) The acetic acid does not fully ionize in water, whereas HCl does.

In which column/group in the periodic table would you expect to find elements with five valence electrons? a) The group that starts with Be b) The group that starts with B c) The group that starts with N d) The group that starts with F e) None of the above

c) The group that starts with N

Which of the following statements about the isotopes of an element is not true? a) They all have the same atomic number. b) They all have the same number of protons. c) They all have the same number of neutrons. d) They all have the same number of electrons. e) They all have identical chemical properties.

c) They all have the same number of neutrons.

Which of the following statements about chemical reactions is false? a) They convert reactants into products. b) They occur when atoms combine or change their bonding partners. c) They may lead to the destruction or creation of energy. d) They may lead to changes in forms of energy. e) They may go to completion.

c) They may lead to the destruction or creation of energy.

_______ is the heaviest isotope of the element whose atomic number is 1. a) Hydrogen b) Deuterium c) Tritium d) Helium e) Titanium

c) Tritium

Why does sodium chloride (NaCl) dissolve in water? a) Sodium and chloride form a polar covalent bond. b) Sodium and chloride can form cations. c) Water is a polar solvent. d) Both a and b e) Both b and c

c) Water is a polar solvent.

Living organisms obey the same laws of _______ and _______ as everything else on our planet. a) biology; chemistry b) mathematics; physics c) chemistry; physics d) biology; physics e) mathematics; chemistry

c) chemistry; physics

Polar molecules a) must form ions in water solution. b) have bonds with an overall negative charge. c) have bonds with an unequal distribution of electric charge. d) have bonds with an overall positive charge. e) have bonds with an equal distribution of electrical charge.

c) have bonds with an unequal distribution of electric charge.

The reactivity of an atom arises from the a) potential energy of the outermost electron shell or valence shell. b) energy difference between the s and p orbitals. c) presence of unpaired electrons in the outermost electron shell or valence shell. d) s-orbital rather than the p-orbital electron shell configuration. e) sum of the potential energies of all electron shells.

c) presence of unpaired electrons in the outermost electron shell or valence shell.

The equation C4H10 + 7 O2 → 4 CO2 + 6 H2O + energy is incorrect because a) two carbon atoms are missing from the products. b) two hydrogen atoms are missing from the products. c) two hydrogen atoms are missing from the reactants. d) two carbons atoms are missing from the reactants. e) Two oxygen atoms are missing in the products.

c) two hydrogen atoms are missing from the reactants.

Water has _______ nonbonding electrons pair(s) and _______ bonding electron pair(s). a) 0; 1 b) 1; 1 c) 1; 2 d) 2; 2 e) 4; 2

d) 2; 2

Carbon atoms can bond _______ hydrogen atoms, and the outer shell of each hydrogen atom then contains _______ electrons. a) 2; 2 b) 2; 4 c) 4; 4 d) 4; 2 e) 8; 2

d) 4; 2

Which of the following is not a way to represent the structure and/or shape of a molecule? a) A Bohr model. b) A space-filling model. c) A ball-and-stick model. d) A polar model. e) A structural formula.

d) A polar model.

Which defines a compound? a) A pure substance with a fixed ratio of elements that cannot form a salt b) A molecule, such as hydrogen gas c) A mixture d) A pure substance with a fixed ratio of two or more elements that are combined through bonds e) A pure substance with a fixed ratio of three or more elements that are combined through bonds

d) A pure substance with a fixed ratio of two or more elements that are combined through bonds

Which of the following best describes the difference between an element and a molecule? a) Elements exist in nature only as parts of molecules. b) Elements always have lower atomic weights than molecules. c) An element is unstable; molecules are stable. d) An element is composed of only one kind of atom; molecules can be composed of more than one kind of atom. e) An element is composed of atoms; a molecule is not.

d) An element is composed of only one kind of atom; molecules can be composed of more than one kind of atom.

Why does a water molecule have a tetrahedral shape? a) Because oxygen bonds to two hydrogen atoms b) Because oxygen contains two sets of unpaired electrons c) Because oxygen contains two sets of paired electrons d) Both a and b

d) Both a and b

Which of the following interactions between atoms is the strongest? a) Hydrogen bonds b) Hydrophobic interactions c) van der Waals forces d) Covalent bonds e) Ionic attraction

d) Covalent bonds

Which of the following properties of water contributes most to the ability of fish in lakes to survive very cold winters? a) Water forms hydrogen bonds. b) Water has a high heat capacity. c) Frozen water is more dense than liquid water. d) Frozen water is less dense than liquid water. e) Water is cohesive.

d) Frozen water is less dense than liquid water.

Which of the following is false? a) A nitrogen-hydrogen triple bond and a nitrogen-hydrogen single bond share electrons in a similar way. b) Bond angles are fixed and determined by the atoms. c) Covalent bonds are considered polar when there is uneven sharing of electrons. d) In a single carbon-hydrogen bond, the bond length varies between molecules. e) The presence of multiple covalent bonds depends on the number of electrons shared between atoms.

d) In a single carbon-hydrogen bond, the bond length varies between molecules.

Rank the elements carbon (C), hydrogen (H), oxygen (O), and phosphorus (P) in decreasing order of the number of covalent bonds they usually form. a) C > P > N > O > H b) P > C > O > N > H c) P > C > O > H > N d) P > C > N > O > H e) P > O > C > N > H

d) P > C > N > O > H

The pH of pure rainwater is 5.5. Samples of rainwater were collected from two areas. The average in area A was pH 5.3, and the average in area B was pH 5.0. Which of the following statements is false? a) Pure rainwater is more acidic than pure water. b) Rainwater from area A is more acidic than pure rainwater. c) Rainwater from area A has a hydrogen ion concentration of 5 × 10-6 M. d) Rainwater from area B is more basic than that from area A. e) Rainwater from area B has a hydrogen ion concentration of 1 × 10-5 M.

d) Rainwater from area B is more basic than that from area A.

A cation has the opposite charge from a(n) a) hydrophilic. b) nonpolar. c) ionic interaction. d) anion. e) complex ion.

d) anion.

The mass number of an element a) equals the number of neutrons in an atom. b) equals the number of protons in an atom. c) equals the number of electrons in an atom. d) equals the number of neutrons plus the number of protons. e) depends on the relative abundances of its electrons and neutrons.

d) equals the number of neutrons plus the number of protons.

Atoms are generally charged and have mass. This statement is a) true, because all atoms have mass and have protons. b) true, because all atoms have mass and have electrons. c) false, because atoms have mass and have neutrons, which cancel out the charge. d) false, because atoms have mass but also have equal numbers of protons and electrons, which results in no (net) charge. e) Both a and b

d) false, because atoms have mass but also have equal numbers of protons and electrons, which results in no (net) charge.

The reaction HCl → H+ + Cl− in the human stomach is an example of the a) cleavage of a hydrophobic bond. b) formation of a hydrogen bond. c) elevation of the pH of the stomach. d) formation of ions by dissociation of an acid. e) formation of polar covalent bonds.

d) formation of ions by dissociation of an acid.

An aqueous solution with a mixture of a _______ acid and its corresponding _______ is called a(n) _______. a) strong; acid; ionic solution b) buffer; base; acid c) strong; base; molar solution d) weak; base; buffer e) strong; acid; buffer

d) weak; base; buffer

If 1 calorie of energy is needed to raise 1 g of water by 1°C, what is the amount of energy needed to raise 15 g of water by 3°C? a) 3 calories b) 9 calories c) 15 calories d) 30 calories e) 45 calories

e) 45 calories

Isotopic analysis of biological samples can be a useful tool in the study of a) the diets of humans. b) the diets of ancient animals. c) migration patterns of ancient people. d) migration patterns of dinosaurs. e) All of the above

e) All of the above

Covalent bonds a) are polar but not nonpolar bonds. b) may be single, double, or triple bonds and can vary in orientation. c) share one or more electron pairs. d) Both a and b e) Both b and c

e) Both b and c

Which of the following statements about isotopes is false? a) Carbon-13 and heavy oxygen are common elements used in isotope analysis. b) Isotopes have virtually the same chemical reactivity. c) Isotopes vary in the number of neutrons but not protons. d) Isotopes have the same atomic number but not the same atomic weight. e) Deuterium is an isotope of hydrogen containing 1 proton and 2 neutrons.

e) Deuterium is an isotope of hydrogen containing 1 proton and 2 neutrons.

The pH scale is a log scale. This means that a) a solution with pH of 7 is twice as acidic as a solution with pH of 9. b) a solution with pH of 7 is twice as acidic as a solution with pH of 5. c) a solution with pH of 7 is 10 times more acidic than a solution with pH of 9. d) a solution with pH of 7 is 10 times more acidic than a solution with pH of 5. e) a solution with pH of 7 is 100 times more acidic than a solution with pH of 9.

e) a solution with pH of 7 is 100 times more acidic than a solution with pH of 9.

Which general chemical principles can be applied to all chemical reactions? a) The number of atoms in the reactants must match the number of atoms in the products. b) Matter can neither be created nor destroyed. c) Energy can change its form but cannot be destroyed or created. d) Both a and b e) a, b, and c

e) a, b, and c

The electronegativity of an atom is a relative measure of the a) number of electrons in the atom's outermost electron shell. b) affinity an atom has for protons and its ability to capture additional protons. c) number of electrons in an atom. d) difference between the number of atoms and the number of protons. e) affinity an atom has for electrons and its ability to capture additional electrons.

e) affinity an atom has for electrons and its ability to capture additional electrons.

An element that contains 10 protons and 10 electrons is likely to a) form covalent bonds with another element. b) be toxic. c) be radioactive. d) form ionic bonds with another element. e) be chemically inert (stable).

e) be chemically inert (stable).

Solid salt, NaCl, is neutral. When dissolved in water, NaCl a) remains as NaCl (does not dissociate). b) dissociates to form Na+ and Cl- ions that do not interact with water molecules. c) dissociates to form Na- and Cl+. d) does not dissociate, but interacts with water molecules. e) dissociates to form Na+ and Cl- ions that do interact with water molecules.

e) dissociates to form Na+ and Cl- ions that do interact with water molecules.

A helium atom contains a) a very large nucleus by volume. b) two hydrogen molecules. c) electrons that have a mass similar to that of protons. d) two positively charged neutrons. e) two negatively charged electrons.

e) two negatively charged electrons.