Question 1

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

Accepted Answer

Because oxygen is more electronegative than hydrogen, creating partial charges and an asymmetrical (bent) shape.

Question 2

Which type of bond is responsible for holding the two strands of DNA together?

Accepted Answer

Hydrogen bonds

Question 3

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

Accepted Answer

$$4$$

Question 4

Why does ice float on liquid water?

Accepted Answer

Hydrogen bonds in ice form a stable lattice that spaces molecules farther apart, making ice less dense.

Question 5

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

Accepted Answer

A polar molecule like ammonia (NH$$_3)$$

Question 6

What is the main reason water has a high specific heat capacity?

Accepted Answer

Hydrogen bonds between water molecules absorb heat when they break and release heat when they form.

Question 7

Which of the following best describes a hydrogen bond?

Accepted Answer

A weak attraction between a partially positive hydrogen atom and a partially negative atom like oxygen or nitrogen.

Question 8

If the pH of a solution changes from 7 to 5, how does the hydrogen ion concentration change?

Accepted Answer

It increases by 100 times.

Question 9

Which property of water allows a water strider to walk on the surface of a pond?

Accepted Answer

Cohesion due to hydrogen bonding

Question 10

Which of the following statements about hydrogen bonds is TRUE?

Accepted Answer

Hydrogen bonds are weak individually but strong in large numbers.

Question 11

A buffer is important in biological systems because it:

Accepted Answer

Maintains a relatively constant pH by accepting or donating H$$^+$$ ions.

Question 12

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

Accepted Answer

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

Question 13

Which of the following is a consequence of water’s high heat of vaporization for living organisms?

Accepted Answer

Evaporative cooling helps organisms maintain stable internal temperatures.

Question 14

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

Accepted Answer

They do not form hydrogen bonds with water and are excluded from aqueous solutions.

Question 15

Which of the following is TRUE about the pH scale?

Accepted Answer

A solution with pH 5 has a higher concentration of H$$^+$$ than a solution with pH 7.

Question 16

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

Accepted Answer

They help stabilize the secondary and tertiary structures of proteins.

Question 17

A molecule has the following properties: symmetrical shape, nonpolar covalent bonds, and is hydrophobic. Which molecule is this most likely to be?

Accepted Answer

Methane (CH$$_4)$$

Question 18

Which of the following statements about acids and bases is correct?

Accepted Answer

Acids donate hydrogen ions (H$$^+) $$and decrease pH.

Question 19

Which emergent property of water is most directly responsible for capillary action in plants?

Accepted Answer

Adhesion

Question 20

If a solution has a pH of 2, what is the hydrogen ion concentration $$[H^+]$$?

Accepted Answer

$$1 	imes 10$$^{-2}$$ M

Water: Structure, Properties, and Biological Importance

Study Guide - Practice Questions