Question 1

Which property of water is primarily responsible for the ability of ice to float on liquid water, and what is the molecular explanation for this phenomenon?

Accepted Answer

Water's expansion upon freezing; hydrogen bonds in ice keep water molecules farther apart, making ice less dense than liquid water.

Question 2

A biologist is studying a plant that transports water from its roots to its leaves. Which two properties of water are most directly responsible for this upward movement against gravity?

Accepted Answer

Cohesion and adhesion

Question 3

Why does water have a high specific heat compared to most other substances?

Accepted Answer

Because hydrogen bonds between water molecules absorb and release heat energy, requiring more energy to change temperature.

Question 4

A scientist adds 1 mole of glucose (molecular mass = 180 g/mol) to enough water to make 1 liter of solution. What is the molarity (M) of the resulting solution?

Accepted Answer

$$1\ \mathrm{M}$$

Question 5

Which of the following best explains why sweating cools the human body?

Accepted Answer

Sweat absorbs heat from the body as it evaporates, due to water's high heat of vaporization.

Question 6

If the pH of a solution changes from 7 to 5, what happens to the concentration of hydrogen ions $$[H^+]$$?

Accepted Answer

It increases by a factor of 100.

Question 7

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

Accepted Answer

A base is a substance that reduces the $$[H^+]$$ concentration of a solution.

Question 8

A marine biologist is concerned about ocean acidification. Which chemical reaction best represents the process by which increased atmospheric $$CO_2$$ leads to lower ocean pH?

Accepted Answer

$$CO_2 + H_2O$$ \rightarrow H_2CO_3$$

Question 9

Which of the following best describes why water is an effective solvent for ionic compounds?

Accepted Answer

Water's polarity allows it to form hydration shells around ions, separating and dissolving them.

Question 10

A solution has a $$[H^+]$$ concentration of $$1 	imes 10$$^{-4}$$\ \mathrm{M}. $$What is the pH of this solution?

Accepted Answer

$$4$$

Question 11

Which property of water is most important for maintaining relatively stable temperatures in coastal regions?

Accepted Answer

High specific heat

Question 12

A researcher observes that oil does not mix with water. Which statement best explains this observation?

Accepted Answer

Oil molecules are hydrophobic due to their nonpolar bonds, so they do not interact favorably with water.

Question 13

Which of the following best describes the role of buffers in biological systems?

Accepted Answer

Buffers minimize changes in $$[H^+]$$ and $$[OH^-]$$ concentrations, helping to maintain a stable pH.

Question 14

Which of the following is a real-world consequence of the expansion of water upon freezing?

Accepted Answer

Ice floats, insulating the water below and allowing aquatic life to survive in winter.

Question 15

A solution contains $$0.5$$ moles of NaCl dissolved in $$1$$ liter of water. What is the molarity of NaCl in the solution?

Accepted Answer

$$0.5\ \mathrm{M}$$

Question 16

Which of the following best explains why water has a high surface tension?

Accepted Answer

Hydrogen bonds between water molecules create a strong cohesive force at the surface.

Question 17

If a solution has a pH of 9, which of the following statements is true?

Accepted Answer

The solution is basic and has a low $$[H^+]$$ concentration.

Question 18

Which of the following is a direct effect of ocean acidification on marine organisms?

Accepted Answer

Decreased availability of carbonate ions, making it harder for organisms to form calcium carbonate shells.

Question 19

A student mixes 10 grams of NaCl (molecular mass = 58.5 g/mol) in enough water to make 500 mL of solution. What is the molarity of NaCl in the solution?

Accepted Answer

$$0.34\ \mathrm{M}$$

Question 20

Which of the following best describes the relationship between temperature and the kinetic energy of water molecules?

Accepted Answer

Temperature represents the average kinetic energy of water molecules.

Chapter 3: Water and Life – Properties and Biological Importance of Water

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