Q: A scientist measures the pH of a solution and finds it to be 4. What is the concentration of hydrogen ions $[H^+]$ in this solution?

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

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

Expansion upon freezing; hydrogen bonds keep water molecules farther apart in ice, making it less dense than liquid water.

Question 2

A scientist measures the pH of a solution and finds it to be 4. What is the concentration of hydrogen ions $[H^+]$ in this solution?

Accepted Answer

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

Question 3

Which of the following best explains why water has a high specific heat compared to other substances?

Accepted Answer

Hydrogen bonds between water molecules require significant energy to break, so more heat is needed to change temperature.

Question 4

A plant transports water from its roots to its leaves against gravity. Which two properties of water are most directly involved in this process?

Accepted Answer

Cohesion and adhesion

Question 5

If the pH of a lake drops from 7 to 5 due to acid rain, by what factor does the hydrogen ion concentration increase?

Accepted Answer

100 times

Question 6

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

Accepted Answer

A buffer is a substance that minimizes changes in pH by reversibly binding hydrogen ions.

Question 7

Which equation correctly defines the relationship between pH and hydrogen ion concentration?

Accepted Answer

$	ext{pH} = -\log [H^+]$

Question 8

Why is water considered a versatile solvent in biological systems?

Accepted Answer

Because water's polarity allows it to form hydration shells around ions and polar molecules.

Question 9

A solution has a pH of 8. Which of the following statements is true about this solution?

Accepted Answer

It is basic and has more $OH^-$ than $H^+$.

Question 10

Which of the following scenarios best illustrates evaporative cooling in living organisms?

Accepted Answer

A person sweating during exercise, where water molecules with the highest kinetic energy leave the skin as vapor.

Question 11

Which of the following is true about hydrophobic substances?

Accepted Answer

They contain relatively nonpolar bonds and do not interact well with water.

Question 12

What is the product of hydrogen ion and hydroxide ion concentrations in any aqueous solution at 25°C?

Accepted Answer

$[H^+][OH^-] = 10^{-14}$

Question 13

Which of the following best explains why coastal areas tend to have milder climates than inland areas?

Accepted Answer

Water's high specific heat allows it to absorb and release large amounts of heat with only slight temperature changes.

Question 14

A weak acid is added to a solution. What is the expected effect on the pH, and why?

Accepted Answer

The pH will decrease slightly because weak acids only partially dissociate, releasing some $H^+$ ions.

Question 15

Which of the following is a real-world consequence of ocean acidification caused by increased atmospheric $CO_2$?

Accepted Answer

Decrease in carbonate ion concentration, threatening organisms that build shells from calcium carbonate.

Question 16

A solution contains $1 	imes 10^{-9}$ M $H^+$. What is its pH?

Accepted Answer

$9$

Question 17

Which of the following best describes the role of hydrogen bonds in water's ability to moderate temperature?

Accepted Answer

Hydrogen bonds absorb and release heat during formation and breaking, minimizing temperature changes.

Question 18

Which of the following would most likely happen if ice were denser than liquid water?

Accepted Answer

Ice would sink, potentially causing bodies of water to freeze solid and threatening aquatic life.

Question 19

A researcher adds a strong base to a solution. What is the expected effect on the concentrations of $H^+$ and $OH^-$?

Accepted Answer

$[H^+]$ decreases and $[OH^-]$ increases.

Question 20

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

Accepted Answer

Oil molecules are nonpolar and cannot interact with water's polar molecules.

Water and Life: Properties, Structure, and Biological Importance

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