Question 1

Which of the following best explains why water (H$$_2O) is a $$polar molecule?

Accepted Answer

Water has polar covalent bonds and an asymmetrical (bent) molecular shape.

Question 2

A hydrogen bond forms between which of the following pairs of atoms?

Accepted Answer

A partially positive hydrogen atom and a partially negative oxygen or nitrogen atom.

Question 3

Which property of water allows it to moderate temperature changes near large bodies of water?

Accepted Answer

High specific heat due to hydrogen bonding.

Question 4

Why does ice float on liquid water?

Accepted Answer

Hydrogen bonds in ice form a stable, open lattice that makes ice less dense than liquid water.

Question 5

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

Accepted Answer

Polar covalent bonds share electrons unequally, while nonpolar covalent bonds share electrons equally.

Question 6

A solution has a hydrogen ion concentration of $$[H^+] = 1 	imes 10$$^{-4}$$ M. What is its pH?

Accepted Answer

$$pH = 4$$

Question 7

Which of the following molecules is most likely to dissolve in water?

Accepted Answer

A polar molecule such as glucose.

Question 8

If the pH of a solution changes from 7 to 5, what happens to the hydrogen ion concentration?

Accepted Answer

It increases by 100 times.

Question 9

Which of the following best explains why salt (NaCl) dissolves easily in water?

Accepted Answer

The partial charges on water molecules surround and separate the Na$$^+$$ and Cl$$^-$$ ions.

Question 10

Which emergent property of water is most directly responsible for the ability of some insects to walk on water?

Accepted Answer

Surface tension due to hydrogen bonding.

Question 11

A molecule of carbon dioxide (CO$$_2) $$contains polar covalent bonds. Why is the molecule itself nonpolar?

Accepted Answer

CO$$_2 is $$linear and symmetrical, so the bond dipoles cancel each other out.

Question 12

Which of the following statements about hydrogen bonds is correct?

Accepted Answer

Hydrogen bonds are much weaker than covalent bonds but are crucial for the structure of DNA and proteins.

Question 13

A buffer is important in biological systems because it:

Accepted Answer

Resists changes in pH by accepting or donating H$$^+$$ ions.

Question 14

Which of the following best describes the relationship between pH and [H$$^+$$]?

Accepted Answer

$$pH = -\log_{10} [H^+]$$

Question 15

Which of the following scenarios best illustrates the concept of cohesion in water?

Accepted Answer

Water droplets forming beads on a car hood due to water molecules sticking to each other.

Question 16

Which of the following is a real-life consequence of water's high heat of vaporization?

Accepted Answer

Sweating cools the body as water evaporates from the skin.

Question 17

Which of the following best explains why nonpolar molecules are hydrophobic?

Accepted Answer

They cannot form hydrogen bonds with water molecules.

Question 18

A solution has a pH of 2. What is the [H$$^+$$] concentration?

Accepted Answer

$$[H^+] = 1 	imes 10$$^{-2}$$ M

Question 19

Which of the following is NOT a direct result of hydrogen bonding in water?

Accepted Answer

Water's ability to dissolve nonpolar substances.

Question 20

Which of the following best describes the role of hydrogen bonds in the structure of DNA?

Accepted Answer

Hydrogen bonds hold the two strands of the DNA double helix together.

Water and Life: Structure, Properties, and Biological Importance

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