Q: A 500 g aqueous solution is 5% NaCl by mass. How many grams of NaCl are present in the solution?

$$\text{mass of NaCl} = \frac{5}{100} \times 500 = 25\ \text{g}$$

Question 1

Which of the following best explains why adding calcium ions (Ca$$^{2+}) to $$clayey, high-sodium soils improves soil structure and plant growth?

Accepted Answer

Ca$$^{2+}$$ ions have a smaller ionic radius and higher charge, promoting flocculation and aggregation of soil particles.

Question 2

Which intermolecular force is primarily responsible for the high boiling point of water compared to other molecules of similar size?

Accepted Answer

Hydrogen bonding

Question 3

A 500 g aqueous solution is 5% NaCl by mass. How many grams of NaCl are present in the solution?

Accepted Answer

$$	ext{mass of NaCl} = \frac{5}{100} 	imes 500 = 25\ 	ext{g}$$

Question 4

Which of the following statements about the process of dissolving NaCl in water is correct?

Accepted Answer

Na$$^{+}$$ and Cl$$^{-}$$ ions are surrounded by water molecules due to ion-dipole interactions.

Question 5

Which of the following best describes the difference between solids, liquids, and gases at the molecular level?

Accepted Answer

Solids have closely packed particles in a fixed arrangement, liquids have closely packed but mobile particles, and gases have widely spaced, rapidly moving particles.

Question 6

Which type of intermolecular force is present in all substances, regardless of their polarity?

Accepted Answer

Dispersion (London dispersion) forces

Question 7

Why does ice float on liquid water?

Accepted Answer

Hydrogen bonding creates an open, cage-like structure in ice, making it less dense than liquid water.

Question 8

Which of the following best explains why larger, heavier molecules generally have higher boiling points?

Accepted Answer

They have stronger dispersion forces due to more electrons and greater surface area.

Question 9

A student dilutes 1.00 L of 1.00 M NaCl solution to 1.80 L. What happens to the number of moles of NaCl and the concentration?

Accepted Answer

The number of moles of NaCl stays the same, but the concentration decreases.

Question 10

Which of the following is the strongest type of intermolecular force found in a sample of NaCl(s)?

Accepted Answer

Ionic bonds

Question 11

Which of the following best describes a hydrogen bond?

Accepted Answer

An attraction between a hydrogen atom bonded to N, O, or F and a lone pair on another N, O, or F atom.

Question 12

Which of the following scenarios best illustrates the concept of 'like dissolves like'?

Accepted Answer

Ethanol (a polar molecule) dissolving in water (a polar solvent).

Question 13

Which of the following is a real-world consequence of excess sodium ions (Na$$^{+}) in $$soil?

Accepted Answer

Soil particles are pushed apart, destroying soil structure and harming plant growth.

Question 14

Which of the following best explains why water is an excellent solvent for ionic compounds?

Accepted Answer

Water molecules are polar and can surround and stabilize both cations and anions through ion-dipole interactions.

Question 15

Which of the following statements about phase changes is correct?

Accepted Answer

Melting and freezing occur at the same temperature for a pure substance.

Question 16

Which of the following best describes the effect of increasing surface area on the boiling point of a molecule, assuming molecular mass is constant?

Accepted Answer

Increasing surface area increases the boiling point due to stronger dispersion forces.

Question 17

Which of the following is an example of a dipole-dipole interaction?

Accepted Answer

Attraction between the positive end of one polar molecule and the negative end of another polar molecule.

Question 18

Which of the following best explains why methane (CH$$_4) $$has a much lower boiling point than water (H$$_2O$$)?

Accepted Answer

Methane is nonpolar and only exhibits weak dispersion forces, while water is polar and forms strong hydrogen bonds.

Question 19

Which of the following is the correct formula for calculating percent by mass of a solute in a solution?

Accepted Answer

$$	ext{Percent by mass} = \frac{	ext{mass of solute}}{	ext{mass of solution}} 	imes 100$$

Question 20

Which of the following best describes the process of sublimation?

Accepted Answer

A solid changes directly into a gas without passing through the liquid state.

Lecture 16

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