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

High surface tension due to cohesion

Question 2

A scientist adds salt to water and observes that the solution now boils at a higher temperature and freezes at a lower temperature than pure water. Which property of solutions does this demonstrate?

Accepted Answer

Colligative properties

Question 3

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

Accepted Answer

Because hydrogen bonds between water molecules absorb heat when they break and release heat when they form

Question 4

Which of the following best explains why ice floats on liquid water?

Accepted Answer

Hydrogen bonds in ice keep water molecules farther apart, making ice less dense than liquid water

Question 5

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 6

Which of the following best describes an amphipathic molecule?

Accepted Answer

A molecule with both hydrophilic and hydrophobic regions

Question 7

A patient is suffering from acidosis (low blood pH). Which buffer system in the blood helps to minimize changes in pH?

Accepted Answer

The carbonic acid-bicarbonate buffer system: $\mathrm{H_2CO_3} \rightleftharpoons \mathrm{HCO_3^-} + \mathrm{H^+}$

Question 8

Which of the following scenarios best illustrates the concept of evaporative cooling?

Accepted Answer

Sweating during exercise, where water evaporates from the skin and cools the body

Question 9

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

Accepted Answer

A base decreases the $\mathrm{H^+}$ concentration of a solution

Question 10

Which property of water is most important for the movement of water from the roots to the leaves in tall trees?

Accepted Answer

Cohesion and adhesion due to hydrogen bonding

Question 11

A researcher wants to prepare a 1 M solution of NaCl. The molecular mass of NaCl is 58.44 g/mol. How many grams of NaCl should be dissolved in 1 liter of water?

Accepted Answer

58.44 grams

Question 12

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 surround and separate ions and polar molecules

Question 13

If the pH of a solution changes from 7 to 5, what happens to the hydrogen ion concentration?

Accepted Answer

It increases by 100-fold

Question 14

Which of the following is a real-life example of an amphipathic molecule forming a structure in water?

Accepted Answer

Phospholipids forming a micelle

Question 15

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

Accepted Answer

Buffers minimize changes in pH by accepting or donating $\mathrm{H^+}$ ions

Question 16

A solution contains 0.5 moles of glucose ($\mathrm{C_6H_{12}O_6}$) dissolved in enough water to make 1 liter of solution. What is the molarity of the solution?

Accepted Answer

0.5 M

Question 17

Which of the following best explains why sweating is an effective way to cool the human body?

Accepted Answer

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

Question 18

Which of the following statements about hydrophobic substances is correct?

Accepted Answer

They are typically nonpolar and do not interact well with water

Question 19

A student adds hydrochloric acid ($\mathrm{HCl}$) to pure water, causing the pH to drop from 7 to 2. Which of the following best describes what has happened?

Accepted Answer

The $[H^+]$ concentration has increased by 100,000 times

Water and Life: Properties, Structure, and Biological Importance

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