Deck 2: Water and Carbon: the Chemical Basis of Life

Question 1

An atom has four electrons in its valence shell. What types of covalent bonds is it capable of forming?

A) single and double only
B) four single bonds only
C) single, double, or triple
D) two double bonds only

Answer 1

C

Question 2

You need to write down information about a molecule that gives the most accurate picture of the relative sizes of the atoms involved and their relationship in space. Which representation would work best?

A) space- filling model
B) structural formula
C) molecular formula
D) ball- and- stick model

Answer 2

A

Question 3

If an atom has a charge of - 2, which of the following must be true?

A) It has two more protons than neutrons.
B) It has two more neutrons than electrons.
C) It has two more electrons than protons.
D) It has two more protons than electrons.

Answer 3

C

Question 4

The structural formula for a certain molecule includes a group symbolized - O. The dash next to the oxygen atom means that a single bond exists to another atom, such as a carbon. Based on the valence of oxygen and the number of bonds it normally forms, what is the charge on the oxygen atom in this case?

A) +1
B) - 1
C) +2
D) - 2

Question 5

You need to write down information about a molecule, but need to indicate only which atoms it contains and how many of each. Which representation would work best?

A) ball- and- stick model
B) space- filling model
C) molecular formula
D) structural formula

Question 6

How many electrons are involved in a double covalent bond?

A) one
B) two
C) three
D) four

Question 7

When the atoms involved in a covalent bond have the same electronegativity, what type of bond results?

A) an ionic bond
B) a nonpolar covalent bond
C) a polar covalent bond
D) a hydrogen bond

Question 8

Nitrogen N) normally forms only three covalent bonds because it has a valence of five. However, ammonium has four covalent bonds, each to a different hydrogen H) atom H has a valence of one). Make a sketch of this molecule. Count the number of electrons in your sketch. Compare this number to the number of valence electrons in one N and four H's. What is the charge on this molecule most likely to be?

A) +1
B) - 1
C) +2
D) - 2

Question 9

What holds electrons in a covalent bond?

A) The electron sharing that occurs makes the atoms involved smaller and more compact.
B) An increase in potential energy, caused by electrical repulsion of the electrons in the bond, holds the electrons.
C) The negative charges on the electrons are attracted by the positive charges on both nuclei.
D) It is the fact that two electrons are paired in the same orbital.

Question 10

If an atom has a charge of +1, which of the following must be true?

A) It has the same number of protons as electrons.
B) It has one more proton than it has electrons.
C) It has one more electron than it has protons.
D) It has two more protons than neutrons.

Question 11

The difference between a polar covalent bond and an ionic bond is that electrons are shared unequally in a polar covalent bond, but are completely transferred i.e., not shared) in an ionic bond.

Question 12

When one of the atoms involved in a covalent bond has a much higher electronegativity than the other atom, what type of bond results?

A) a polar covalent bond
B) a nonpolar covalent bond
C) a double bond
D) a hydrogen bond

Question 13

An atom has six electrons in its valence shell. How many single covalent bonds would you expect it to form in most circumstances?

A) one
B) two
C) three
D) six

Question 14

If an atom is electrically neutral, which of the following must be true?

A) It has the same number of neutrons as electrons.
B) It has the same number of protons as electrons.
C) It has at least one more electron than it has protons.
D) It has the same number of protons as neutrons.

Question 15

When are atoms most stable?

A) when all electrons are paired
B) when they have the fewest possible valence electrons
C) when all of the electron orbitals in the valence shell are filled
D) when they have the maximum number of unpaired electrons

Question 16

How many electrons are involved in a single covalent bond?

A) one
B) two
C) three
D) four

Question 17

How many electrons are involved in a triple covalent bond?

A) two
B) three
C) six
D) nine

Question 18

There are four elements that make up 95% of all matter found in organisms. Which of the following is not one of these?

A) oxygen
B) hydrogen
C) calcium
D) nitrogen

Question 19

Why is water capable of forming hydrogen bonds?

A) It is highly polar.
B) The oxygen atom carries a partial negative charge.
C) The hydrogen atoms carry partial positive charges.
D) All of the above apply.

Question 20

How can you determine the approximate mass of an atom in atomic mass units?

A) Add up the number of protons and electrons.
B) Take the number of protons minus the number of electrons.
C) Add up the number of protons, electrons, and neutrons.
D) Add up the number of protons and neutrons.

Question 21

Water molecules are able to form hydrogen bonds with which of the following?

A) compounds that have nonpolar covalent bonds
B) compounds that have polar covalent bonds
C) methane gas CH₄) molecules
D) oxygen gas O₂) molecules
E) compounds that are not soluble in water

Question 22

While water has many exceptional and useful properties, which is the rarest property among compounds?

A) Water is a solvent.
B) Water has surface tension.
C) Water has a high heat capacity.
D) Solid water is less dense than liquid water.

Question 23

Which reaction is most spontaneous?

A) a reaction that is slightly exothermic and leads to a huge increase in entropy
B) a reaction that is slightly endothermic and leads to a huge decrease in entropy
C) a reaction that is highly exothermic and leads to a huge decrease in entropy
D) a reaction that is slightly exothermic and leads to a slight increase in entropy

Question 24

Why is water such a good solvent?

A) It can participate in hydrogen bonds.
B) Most polar and charged substances dissolve in it.
C) It is highly polar.
D) All of the above apply.

Question 25

Ice melts spontaneously at room temperature, even though the process is endothermic. How is this possible?

A) There is a large increase in entropy.
B) OH is small, so melting still obeys the second law of thermodynamics.
C) The Gibbs free- energy relationship does not apply to phase changes such as melting.
D) There is an increase in free energy when ice melts.

Question 26

Why are some reactions exothermic?

A) The products have higher entropy are more disordered) than the reactants.
B) They are spontaneous.
C) The products have lower potential energy than the reactants.
D) They are nonspontaneous.

Question 27

A pH of 7 is neutral due to the dissociation of water molecules in pure water. How many molecules of water have broken down into a hydroxide ion and a hydronium ion at pH 7?

A) 1 in 1 million
B) 1 in 10 million
C) 1 in 100 million
D) 1 in 1 billion

Question 28

The cities of Portland, Oregon, and Minneapolis, Minnesota, are at about the same latitude, but Minneapolis has much hotter summers and much colder winters than Portland. Why? Portland is near the Pacific Ocean; Minneapolis is near a number of large lakes.)

A) The ocean is so large that it has a highly moderating influence on temperature.
B) Minneapolis is much windier, due to its location in the middle of a continent.
C) They are not at exactly the same latitude.
D) Freshwater is more likely to freeze than saltwater.

Question 29

Which statement best summarizes the essence of chemical evolution?

A) Entropy increased.
B) Instead of being radiated back to space, energy in the form of sunlight or heat was retained in the oceans and atmosphere.
C) An increasing number of exothermic reactions occurred.
D) Energy in the form of sunlight or heat was transformed into chemical energy.

Question 30

Consider the following reaction at equilibrium: CO₂ + H₂O -H₂CO₃. What would be the effect of adding additional H₂CO₃?

A) Nothing would happen, because the reactants and products are in equilibrium.
B) The amounts of CO₂ and H₂O would decrease.
C) It would drive the equilibrium dynamics to the right.
D) It would drive the equilibrium dynamics to the left.

Question 31

In a single molecule of water, two hydrogen atoms are bonded to a single oxygen atom by what type of bond or interaction?

A) nonpolar covalent bonds
B) ionic bonds
C) van der Waals interaction
D) polar covalent bonds
E) hydrogen bonds

Question 32

A solution with a pH of 5 has how many more protons in it than a solution with a pH of 7?

A) 5 times
B) 10 times
C) 100 times
D) 1,000 times

Question 33

Why do chemical reactions tend to speed up when the reactants are heated?

A) The reactants have greater energy.
B) The reactants collide more often.
C) The reactants move faster.
D) All of the above apply.

Question 34

Which of the following unique properties of water is responsible for explaining how water can move from the roots of plants to their leaves against gravity?

A) Water can dissociate into H⁺ and OH^- .
B) Water is cohesive.
C) Water is an excellent solvent.
D) Water is denser as a liquid than a solid.
E) Water spontaneously dissociates into hydrogen ions and hydroxide ions.

Question 35

Which of the following is a violation of the first law of thermodynamics?

A) All of the energy in the universe today was present when the Big Bang occurred.
B) A hydrogen bomb can destroy a large city with only a few pounds of explosive material.
C) The amount of energy stored in a plant's cell as sugars after undergoing photosynthesis is less than the amount of sunlight it absorbed.
D) The universe will eventually die, and it will have no energy left in it.

Question 36

Why do chemical reactions tend to speed up when the concentration of the reactants is increased?

A) The reactants have greater energy.
B) The reactants move faster.
C) The reactants collide more often.
D) All of the above apply.

Question 37

In the Gibbs free- energy relationship, why is the T term necessary?

A) The free- energy change caused by a change in electrical charge is a function of temperature.
B) The free- energy change caused by a change in potential energy is a function of temperature.
C) The free- energy change caused by a change in entropy is a function of temperature.

Question 38

What does it mean to say a system has a AG equal to zero?

A) The system is perfectly ordered no entropy).
B) The total amount of potential energy in the system is zero.
C) The system is at equilibrium.
D) The system does not release or absorb heat.

Question 39

Which of the following effects is produced by the high surface tension of water?

A) Water flows upward from the roots to the leaves in plants.
B) Lakes don't freeze solid in winter despite low temperatures.
C) A water strider can walk across the surface of a small pond.
D) Evaporation of sweat from the skin helps to keep people from overheating.
E) Organisms resist temperature changes, although they give off heat due to chemical reactions.

Question 40

The slight negative charge at one end of one water molecule is attracted to the slight positive charge of another water molecule. What is this attraction called?

A) a van der Waals interaction
B) a covalent bond
C) a hydrophilic bond
D) a hydrogen bond
E) an ionic bond

Question 41

Experiments by Stanley Miller in the 1950s demonstrated that the first organic molecules on Earth

A) were catalysts composed of simple amino acids and most likely formed in an extraterrestrial environment and were deposited on Earth via asteroids.
B) most likely formed in an extraterrestrial environment and were deposited on Earth via asteroids.
C) were nucleic acids such as RNA and DNA.
D) could have formed abiotically in a reducing atmosphere containing hydrogen, methane, ammonia, and water vapour.
E) were simple carbohydrates like glucose.

Question 42

Why would the spontaneous formation of formaldehyde and hydrogen cyanide not take place on Earth today as much as on the prebiotic Earth?

A) Atmospheric conditions on Earth, such as the presence of oxygen, have changed.
B) The sun has changed its output.
C) Microorganisms break these down immediately.

Question 43

During chemical evolution, which of the following occurred in the molecules involved?

A) Entropy decreased while potential energy increased.
B) Entropy stayed constant while potential energy increased.
C) Entropy increased while potential energy increased.

Question 44

How many times can humans be sure the switch from nonlife to life has happened in the universe?

A) four times
B) once
C) twice
D) 42 times

Question 45

Which of the following tends to make chemical reactions spontaneous?

A) The reactants have lower potential energy than the products.
B) The temperature is low.
C) The reactants are more ordered than the products.
D) The pressure is low.

Question 46

You've been asked to analyze a reaction that took place at 300°K. AH was - 150 and AS was +0.4. Is the reaction endothermic or exothermic?

A) exothermic
B) endothermic
C) You cannot tell unless you know the potential energy of the reactants and products.
D) You cannot tell unless you know the amount of disorder in the reactants and products.

Question 47

Carbon is an important element for biology because

A) carbon is so rare, organisms conserve it highly.
B) of the variety of carbon skeletons and functional groups that can be built on them.
C) it has very high electronegativity and forms highly stable bonds.
D) it has the ability to form six covalent bonds.

Question 48

The first chemicals that provided potential energy on Earth may have been formaldehyde and hydrogen cyanide. While these were produced by sunlight- driven reactions, they also occur around deep- sea vents. If the first organisms on Earth evolved around these vents, the first life on Earth was

A) photosynthetic and obtained energy from the sun.
B) herbivorous and obtained energy from plants.
C) chemosynthetic and obtained energy from chemicals.
D) carnivorous and obtained energy from animals.

Question 49

Which of the following models is described by the idea that dissolved gases came in contact with minerals lining the walls of deep- sea vents and formed more complex organic molecules?

A) the atmospheric model
B) the surface metabolism model
C) the extraterrestrial model
D) the prebiotic soup model

Question 50

Consider the experiment that Stanley Miller did to simulate chemical evolution. Recall that a glass flask held the reduced gases NH₃, CH₄, and H₂ and that the gases were exposed to electrical sparks. What is the null hypothesis in the experiment?

A) Chemical evolution does not occur.
B) Chemical evolution requires the presence of reduced molecules.
C) Chemical evolution occurs only on Earth.
D) Chemical evolution requires a source of kinetic energy.
E) Chemical evolution requires continuous heating.

Question 51

Why is carbon so important in biology?

A) It is a common element on Earth.
B) It has very little electronegativity, making it a good electron donor.
C) It forms up to four covalent bonds.
D) It bonds to only a few other elements.

Question 52

Many scientific probes sent to other parts of the solar system are looking for signs of something so far known to exist only on Earth, namely

A) carbon.
B) life.
C) nitrogen.
D) gold.

Question 53

Chemical evolution refers to which of the following?

A) Water condensed to form the first oceans.
B) Earth's crust solidified, even as massive bombardment from outer space continued.
C) Small molecules reacted to form larger, more complex molecules.
D) Large molecules tended to break apart because of the intense sunlight and heat from volcanoes.