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

$$1 \times 10$$^{-4}$$\ \mathrm{M}$$

Question 1

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

Accepted Answer

Hydrogen bonds in ice are more stable, causing water molecules to be farther apart, making ice less dense than liquid water.

Question 2

A patient is diagnosed with goiter, a swelling of the thyroid gland. Which trace element deficiency is most likely responsible for this condition?

Accepted Answer

Iodine (I)

Question 3

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 4

A sodium atom ($$^{23}\mathrm{Na}) $$has an atomic number of 11. How many neutrons does it have?

Accepted Answer

$$12$$

Question 5

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by the sharing of valence electrons between atoms.

Question 6

Which property of water allows it to moderate temperature in living organisms?

Accepted Answer

High specific heat

Question 7

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

Accepted Answer

$$1 	imes 10$$^{-4}$$\ \mathrm{M}$$

Question 8

Which of the following best explains why salt (NaCl) dissolves easily in water?

Accepted Answer

Water's polarity allows it to surround and separate Na$$^+$$ and Cl$$^-$$ ions, forming hydration shells.

Question 9

Which of the following is an example of an emergent property?

Accepted Answer

The ability of sodium chloride (NaCl) to form crystals, which is not a property of sodium or chlorine alone.

Question 10

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

Accepted Answer

Buffers minimize changes in pH by accepting or donating hydrogen ions.

Question 11

A molecule of ammonia ($$\mathrm{NH}_3) $$acts as a base in water. Which reaction best represents this behavior?

Accepted Answer

$$\mathrm{NH}_3 + \mathrm{H}^+ \rightleftharpoons \mathrm{NH}_4^+$$

Question 12

Which of the following statements about van der Waals interactions is correct?

Accepted Answer

They are weak attractions that occur when molecules are very close together due to temporary charge differences.

Question 13

Which of the following best explains why water is an effective solvent for many biological molecules?

Accepted Answer

Water's polarity allows it to form hydrogen bonds with polar and ionic substances.

Question 14

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

Accepted Answer

Evaporative cooling helps regulate body temperature in organisms such as humans.

Question 15

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

Accepted Answer

It increases by a factor of 100.

Question 16

Which of the following best describes the difference between a compound and an element?

Accepted Answer

A compound consists of two or more elements in a fixed ratio, while an element cannot be broken down by chemical reactions.

Question 17

Which of the following is true about the chemical behavior of an atom?

Accepted Answer

It is determined by the number of electrons in the valence shell.

Question 18

Which of the following best explains why carbonic acid ($$\mathrm{H}_2\mathrm{CO}_3) $$acts as a buffer in human blood?

Accepted Answer

It can both donate and accept hydrogen ions, minimizing changes in pH.

Question 19

Which of the following is a real-world consequence of ocean acidification caused by increased atmospheric $$\mathrm{CO}_2$$?

Accepted Answer

Decreased carbonate ion concentration, making it harder for marine organisms to form shells.

Question 20

Which of the following best describes the difference between hydrophilic and hydrophobic substances?

Accepted Answer

Hydrophilic substances have an affinity for water due to polar or charged regions, while hydrophobic substances do not interact with water because they are nonpolar.

Chapter 2: The Chemical Context of Life – Study Notes

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