Question 1

Which of the following best explains why water is considered a polar molecule?

Accepted Answer

Water has polar covalent bonds and an asymmetrical shape, resulting in partial charges.

Question 2

A molecule of methane ($$\mathrm{CH_4$}) is $$nonpolar because:

Accepted Answer

Its shape is symmetrical, so any partial charges cancel out.

Question 3

Which emergent property of water is most directly responsible for the ability of trees to transport water from roots to leaves?

Accepted Answer

Cohesion and adhesion due to hydrogen bonding

Question 4

Given the electronegativities: $$\mathrm{H = 2.1}$$, $$\mathrm{O = 3.44}$$, what is the difference in electronegativity between O and H, and what type of bond does this indicate?

Accepted Answer

Difference = $$1.34$$; polar covalent bond

Question 5

Why does ice float on water, and why is this important for aquatic life?

Accepted Answer

Ice is less dense than liquid water because hydrogen bonds form a stable, open structure; this allows aquatic life to survive under the ice.

Question 6

Which of the following statements about hydrogen bonds is TRUE?

Accepted Answer

Hydrogen bonds are formed by the attraction between a partially positive hydrogen and a partially negative atom (like O or N).

Question 7

A solution has a hydrogen ion concentration of $$[\mathrm{H^+}] = 1 	imes 10$$^{-3}$$\ \mathrm{M}. $$What is its pH?

Accepted Answer

$$3$$

Question 8

Which of the following best describes the relationship between pH and hydrogen ion concentration?

Accepted Answer

As pH increases, $$[\mathrm{H^+}]$$ decreases.

Question 9

Which property of water allows it to moderate temperature changes in coastal regions?

Accepted Answer

High specific heat due to hydrogen bonding

Question 10

Which of the following molecules would dissolve most easily in water?

Accepted Answer

A polar molecule like ammonia ($$\mathrm{NH_3$})$$

Question 11

What is the main reason salt ($$\mathrm{NaCl}) $$dissolves in water?

Accepted Answer

Water's partial charges attract and surround the $$\mathrm{Na^+}$$ and $$\mathrm{Cl^-}$$ ions, separating them.

Question 12

Which of the following is NOT an emergent property of water due to hydrogen bonding?

Accepted Answer

Hydrophobicity

Question 13

A protein's structure is stabilized by hydrogen bonds. What would likely happen to the protein if the pH of its environment changed drastically?

Accepted Answer

The protein would denature due to disruption of hydrogen bonds.

Question 14

Which of the following best describes a buffer in biological systems?

Accepted Answer

A buffer resists changes in pH by accepting or donating $$\mathrm{H^+}$$ ions.

Question 15

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

Accepted Answer

Acids donate hydrogen ions ($$\mathrm{H^+}) $$and decrease pH.

Question 16

A solution of pH 3 has how much more $$[\mathrm{H^+}]$$ than a solution of pH 6?

Accepted Answer

1000x more

Question 17

Which of the following best describes the bond between oxygen and hydrogen within a water molecule?

Accepted Answer

A polar covalent bond

Question 18

Which of the following is a real-world example of water's high heat of vaporization?

Accepted Answer

Sweating cools the body as water evaporates from the skin.

Question 19

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

Accepted Answer

They do not form hydrogen bonds and are not soluble in water.

Question 20

Which of the following is TRUE about the pH scale?

Accepted Answer

A difference of one unit represents a ten-fold change in $$[\mathrm{H^+}]$$ concentration.

Water: Structure, Properties, and Biological Importance

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