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

Question 1

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

Accepted Answer

Water molecules have a bent shape and partial charges, allowing them to form hydrogen bonds with charged or polar solutes.

Question 2

A molecule of ammonia ($$NH_3) $$forms hydrogen bonds with water. Which property of ammonia allows this interaction?

Accepted Answer

Ammonia contains nitrogen, which is highly electronegative, creating partial charges that allow hydrogen bonding.

Question 3

Which statement correctly describes the difference between covalent and ionic bonds?

Accepted Answer

Covalent bonds involve the sharing of electrons between atoms, while ionic bonds involve the complete transfer of electrons from one atom to another.

Question 4

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

Accepted Answer

Ice forms an open crystal structure stabilized by hydrogen bonds, making it 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 property of water is primarily responsible for the movement of water from the roots to the leaves of plants against gravity?

Accepted Answer

Cohesion and adhesion due to hydrogen bonding

Question 7

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 8

Which of the following functional groups acts as a base by attracting protons?

Accepted Answer

Amino group ($$-NH_2$)

Question 9

A scientist adds a base to a solution, causing the pH to increase. What happens to the concentration of hydronium ions ($$[H_3O^+]$$)?

Accepted Answer

It decreases.

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 protons.

Question 11

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

Accepted Answer

Water resists changes in temperature, helping to stabilize internal and external environments.

Question 12

Which of the following best explains why carbon is the backbone of biological molecules?

Accepted Answer

Carbon can form up to four covalent bonds, allowing for a variety of stable and complex molecular structures.

Question 13

Which of the following statements about hydrophobic molecules is correct?

Accepted Answer

Hydrophobic molecules are uncharged and nonpolar, and do not dissolve in water.

Question 14

A polymer is formed from monomers by which type of reaction?

Accepted Answer

Condensation (dehydration) reaction, which releases a water molecule.

Question 15

Which of the following best describes the electron-sharing continuum in chemical bonds?

Accepted Answer

It ranges from equal sharing in nonpolar covalent bonds, to unequal sharing in polar covalent bonds, to complete transfer in ionic bonds.

Question 16

If a molecule has a molecular formula of $$C_6H_{12}O_6$, what is its molecular weight? (Atomic weights: C = 12, H = 1, O = 16)

Accepted Answer

$$180 \ \mathrm{g/mol}$$

Question 17

Which of the following is true about acids and bases in aqueous solutions?

Accepted Answer

Acids increase the concentration of hydronium ions ($$H_3O^+$$), while bases decrease it.

Question 18

Which of the following best describes the process of hydrolysis in biological systems?

Accepted Answer

Hydrolysis breaks polymers into monomers by adding a water molecule.

Question 19

Which of the following statements about the valence of an atom is correct?

Accepted Answer

The valence of an atom is the number of unpaired electrons in its outermost shell.

Question 20

Which of the following is a real-world example of water's high heat of vaporization being important for living organisms?

Accepted Answer

Sweating cools the human body because water absorbs a large amount of heat as it evaporates.

Water and Carbon: The Chemical Basis of Life – Chapter 2

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