Question 1

Which of the following statements best explains why water is an excellent solvent for ionic compounds such as NaCl?

Accepted Answer

Water molecules have partial positive and negative charges that interact with ions, allowing them to dissolve.

Question 2

A carbon atom has an atomic number of 6 and a mass number of 14. How many neutrons does this atom have?

Accepted Answer

$$14 - 6 = 8$$ neutrons

Question 3

Which property of water allows it to moderate temperature changes in organisms and environments?

Accepted Answer

Water's high specific heat due to hydrogen bonding

Question 4

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by the sharing of electron pairs between atoms

Question 5

Why does ice float on liquid water?

Accepted Answer

Ice is less dense than liquid water because its molecules form a crystalline lattice with more open space.

Question 6

Which of the following is true about isotopes of an element?

Accepted Answer

They have the same number of protons but different numbers of neutrons.

Question 7

A sodium atom (Na) has 11 protons and 12 neutrons. What is its mass number?

Accepted Answer

$$11 + 12 = 23$$

Question 8

Which of the following best explains why water molecules are polar?

Accepted Answer

Oxygen is more electronegative than hydrogen, creating partial charges on the molecule.

Question 9

Which of the following is a direct consequence of water's cohesion?

Accepted Answer

Water molecules stick to each other, allowing surface tension.

Question 10

A chlorine atom has 17 protons and 18 neutrons. What is its atomic number and mass number?

Accepted Answer

Atomic number: 17, Mass number: $$17 + 18 = 35$$

Question 11

Which of the following best describes the octet rule?

Accepted Answer

Atoms are stable when their outer shell contains 8 electrons.

Question 12

Which of the following is a property of hydrophobic molecules?

Accepted Answer

They are repelled by water and do not dissolve.

Question 13

Which of the following best explains why carbon is able to form large, complex molecules?

Accepted Answer

Carbon has four valence electrons, allowing it to form up to four covalent bonds.

Question 14

Which of the following best describes the difference between a polar covalent bond and a nonpolar covalent bond?

Accepted Answer

Polar covalent bonds involve unequal sharing of electrons; nonpolar covalent bonds involve equal sharing.

Question 15

If an atom has 8 protons, 8 neutrons, and 8 electrons, what is its atomic mass and atomic number?

Accepted Answer

Atomic mass: $$8 + 8 = 16$$, Atomic number: 8

Question 16

Which of the following scenarios best illustrates adhesion?

Accepted Answer

Water molecules sticking to the sides of a glass tube, causing a meniscus

Question 17

Which of the following is a direct result of water's high heat of vaporization?

Accepted Answer

Water helps organisms maintain a stable internal temperature.

Question 18

Which of the following best explains why salt (NaCl) dissolves in water but oil does not?

Accepted Answer

Salt is hydrophilic and interacts with water's charges, while oil is hydrophobic and does not interact with water.

Question 19

Which of the following statements about valence electrons is correct?

Accepted Answer

Valence electrons are the electrons in the outermost shell and determine chemical reactivity.

Question 20

Which of the following best describes the role of hydrogen bonds in water's properties?

Accepted Answer

Hydrogen bonds allow water to have a high specific heat, surface tension, and act as a solvent.

Atoms, Ions, Molecules, and Water: Foundations of Chemical Evolution in Biology

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