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 of the following best explains why water is considered a polar molecule?

Accepted Answer

Because the oxygen atom is more electronegative than the hydrogen atoms, resulting in a partial negative charge on oxygen and partial positive charges on hydrogens.

Question 2

A student dissolves table salt (NaCl) in water. Which type of bond is broken in the NaCl, and which type of interaction forms between the ions and water molecules?

Accepted Answer

Ionic bonds are broken; ion-dipole interactions form between ions and water.

Question 3

Which of the following best describes a hydrogen bond?

Accepted Answer

A weak attraction between a partially positive hydrogen atom in one molecule and a partially negative atom (such as oxygen or nitrogen) in another molecule.

Question 4

Which of the following statements about electronegativity and covalent bonds is correct?

Accepted Answer

A greater difference in electronegativity between two atoms in a covalent bond results in a more polar bond.

Question 5

Rank the following types of chemical bonds from strongest to weakest: covalent, ionic, hydrogen.

Accepted Answer

Covalent \u003e Ionic \u003e Hydrogen

Question 6

Which property of water allows it to moderate Earth's temperature by absorbing and releasing large amounts of heat with only slight changes in its own temperature?

Accepted Answer

High specific heat

Question 7

Why does ice float on liquid water?

Accepted Answer

Because hydrogen bonding causes water molecules in ice to be arranged in a lattice that is less dense than liquid water.

Question 8

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 9

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

Accepted Answer

Because water is polar and can form hydrogen bonds and ion-dipole interactions with solutes.

Question 10

Which of the following is an example of cohesion in water?

Accepted Answer

Water molecules sticking to each other, allowing insects to walk on water.

Question 11

A scientist adds a base to a solution. What happens to the concentration of $$[H^+]$$ and the pH?

Accepted Answer

$$[H^+]$$ decreases and pH increases.

Question 12

Which of the following best describes the difference between a polar covalent bond and a nonpolar covalent bond?

Accepted Answer

A polar covalent bond has an unequal sharing of electrons due to a difference in electronegativity, while a nonpolar covalent bond has equal sharing.

Question 13

Which of the following is a direct result of water's high surface tension?

Accepted Answer

Small insects can walk on the surface of water without sinking.

Question 14

If a molecule is described as hydrophilic, what does this mean?

Accepted Answer

It has an affinity for water and can dissolve in water.

Question 15

Which of the following best explains why water can dissociate into $$H_3O^+$$ and $$OH^-$$ ions?

Accepted Answer

Because hydrogen bonds allow protons to transfer between water molecules, forming hydronium and hydroxide ions.

Question 16

Which of the following scenarios best illustrates adhesion?

Accepted Answer

Water molecules sticking to the walls of a plant's xylem vessels, helping water move upward.

Question 17

A solution has a pH of 9. Which of the following best describes the solution?

Accepted Answer

It is basic, with a low concentration of $$[H^+]$$ ions.

Question 18

Which of the following is a consequence of water's ability to form hydrogen bonds?

Accepted Answer

Water has a high boiling point relative to its molecular weight.

Question 19

Which of the following best describes van der Waals interactions?

Accepted Answer

Weak attractions between molecules that occur when atoms are close together, important when many such interactions are present.

Chapter 3 – Water and Life: Chemical Bonds, Water Properties, and Biological Importance

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