Q: A solution has a pH of 4. What is the concentration of hydrogen ions $$[H^+] in $$this solution?

$$[H^+] = 1 \times 10$$^{-4}$$ \ \mathrm{M}$$

Question 1

Which property of water is primarily responsible for the ability of some insects, such as water striders, to walk on the surface of a pond without sinking?

Accepted Answer

Cohesion due to hydrogen bonding

Question 2

Why does ice float on liquid water, and what would be the ecological consequence if it did not?

Accepted Answer

Ice is less dense than liquid water because hydrogen bonds keep molecules farther apart; if it sank, bodies of water would freeze solid, threatening aquatic life.

Question 3

Which of the following best explains why coastal cities tend to have milder climates than inland cities at the same latitude?

Accepted Answer

Water has a high specific heat, allowing it to absorb and release large amounts of heat with little temperature change.

Question 4

A solution has a pH of 4. What is the concentration of hydrogen ions $$[H^+] in $$this solution?

Accepted Answer

$$[H^+] = 1 	imes 10$$^{-4}$$ \ \mathrm{M}$$

Question 5

Which of the following best describes why water is an effective solvent for ionic and polar substances?

Accepted Answer

Water molecules are polar, allowing them to form hydration shells around ions and polar molecules.

Question 6

Which of the following equations correctly represents the dissociation of water?

Accepted Answer

$$2 \ \mathrm{H_2O} \rightleftharpoons \mathrm{H_3O^+} + \mathrm{OH^-}$$

Question 7

A buffer solution contains a weak acid and its conjugate base. What happens when a small amount of acid is added to this solution?

Accepted Answer

The buffer accepts the added $$H^+$$ ions, minimizing the change in pH.

Question 8

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

Accepted Answer

Evaporative cooling helps regulate body temperature.

Question 9

If the concentration of $$[OH^-] in a $$solution is $$1 	imes 10$$^{-9}$$ \ \mathrm{M} at 25$$°C, what is the pH of the solution?

Accepted Answer

pH = 5

Question 10

Which of the following best explains why oil does not dissolve in water?

Accepted Answer

Oil molecules are nonpolar and cannot form hydrogen bonds with water.

Question 11

A scientist wants to prepare 1 liter of a 0.5 M NaCl solution. The molecular mass of NaCl is 58.44 g/mol. How many grams of NaCl should be used?

Accepted Answer

29.22 g

Question 12

Which of the following scenarios illustrates the importance of water’s cohesive and adhesive properties in nature?

Accepted Answer

Water moving upward from roots to leaves in a tall tree.

Question 13

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

Accepted Answer

An acid increases the $$[H^+]$$ concentration in a solution.

Question 14

Ocean acidification is primarily caused by which of the following processes?

Accepted Answer

Absorption of atmospheric $$CO_2 by $$oceans, forming carbonic acid

Question 15

Which of the following best describes the relationship between $$[H^+]$$ and $$[OH^-] in $$pure water at 25°C?

Accepted Answer

$$[H^+]$$ equals $$[OH^-]$$ and both are $$1 	imes 10$$^{-7}$$ \ \mathrm{M}$$

Question 16

A marine biologist observes that coral reefs are declining in areas with increased ocean acidification. What is the most likely explanation for this observation?

Accepted Answer

Acidification decreases carbonate ion concentration, reducing the ability of corals to form calcium carbonate skeletons.

Question 17

Which of the following is an example of a hydrophilic substance?

Accepted Answer

Table salt (NaCl)

Question 18

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

Accepted Answer

Evaporation of sweat removes heat from the body due to water’s high heat of vaporization.

Question 19

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

Accepted Answer

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

Question 20

A solution is made by dissolving 10 g of glucose (molecular mass = 180 g/mol) in enough water to make 0.5 L of solution. What is the molarity (M) of the solution?

Accepted Answer

0.11 M

Water and Life: Properties, Structure, and Biological Importance

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