Q: A solution has a pH of 4. What is the concentration of hydrogen ions $[H^+]$ in the 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 the water strider, to walk on the surface of a pond without sinking?

Accepted Answer

High surface tension due to hydrogen bonding

Question 2

Why does ice float on liquid water, and what would be the consequence for aquatic life if ice sank?

Accepted Answer

Ice is less dense than liquid water because hydrogen bonds in ice are more ordered, creating more space between molecules; if ice sank, bodies of water would freeze solid, making life impossible.

Question 3

A beaker contains 100 g of water at $25^\circ C$. How much heat (in calories) is required to raise the temperature of the water to $35^\circ C$? (Specific heat of water = $1 \ \mathrm{cal}/(\mathrm{g} \cdot ^\circ C)$)

Accepted Answer

$1000 \ \mathrm{cal}$

Question 4

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, so it absorbs and releases heat slowly, moderating temperature changes.

Question 5

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

Accepted Answer

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

Question 6

Which of the following statements about hydrogen bonding in water is correct?

Accepted Answer

Hydrogen bonds form between the hydrogen atom of one water molecule and the oxygen atom of another water molecule.

Question 7

A plant is able to transport water from its roots to its leaves against gravity. Which combination of water's properties is most directly responsible for this process?

Accepted Answer

Cohesion and adhesion

Question 8

Which of the following best describes a hydrophobic substance?

Accepted Answer

A substance that does not have an affinity for water because it contains mostly nonpolar bonds

Question 9

A buffer solution is added to a beaker of pure water. Which of the following best describes the function of the buffer?

Accepted Answer

It minimizes changes in $[H^+]$ and $[OH^-]$ when acids or bases are added.

Question 10

Which of the following scenarios best illustrates evaporative cooling in a real-world context?

Accepted Answer

A person sweats during exercise, and as the sweat evaporates, their body temperature decreases.

Question 11

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

Accepted Answer

Water molecules are polar and can form hydration shells around ions and polar molecules.

Question 12

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 13

Which of the following is NOT an emergent property of water that contributes to Earth's suitability for life?

Accepted Answer

Low specific heat

Question 14

A scientist adds a strong acid to a buffered solution. What is the expected outcome regarding the pH of the solution?

Accepted Answer

The pH will remain relatively stable due to the buffer.

Question 15

Which of the following best describes the relationship between homeostasis and water in living organisms?

Accepted Answer

Water's properties help maintain stable internal conditions, such as temperature and pH, which are essential for homeostasis.

Question 16

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

Accepted Answer

An acid is a substance that increases the $[H^+]$ concentration of a solution.

Question 17

Which of the following best explains why sweating is an effective mechanism for cooling the human body?

Accepted Answer

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

Question 18

Which of the following would most likely dissolve in water?

Accepted Answer

An ionic compound such as NaCl

Question 19

Which of the following best describes the dynamic equilibrium of water dissociation?

Accepted Answer

Water molecules dissociate and reform at the same rate, maintaining constant concentrations of $H^+$ and $OH^-$.

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

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