Q: A student measures the mass of a metal cylinder as 12.34 g and its volume as 4.56 mL. What is the density of the cylinder, and how many significant figures should the answer have?

$$\text{Density} = \frac{12.34\ \mathrm{g}}{4.56\ \mathrm{mL}} = 2.706\ \mathrm{g/mL}$$, reported as 2.71 g/mL (3 significant figures, matching the least precise measurement)

Question 1

Which of the following best describes an intensive property of matter, and which is an example of such a property?

Accepted Answer

An intensive property does not depend on the amount of substance present; density is an example.

Question 2

A student measures the mass of a metal cylinder as 12.34 g and its volume as 4.56 mL. What is the density of the cylinder, and how many significant figures should the answer have?

Accepted Answer

$$	ext{Density} = \frac{12.34\ \mathrm{g}}{4.56\ \mathrm{mL}} = 2.706\ \mathrm{g/mL}$$, reported as 2.71 g/mL (3 significant figures, matching the least precise measurement)

Question 3

Which of the following statements about the periodic law is correct?

Accepted Answer

The periodic law states that the properties of elements are periodic functions of their atomic numbers.

Question 4

A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 5

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

Accepted Answer

Water is polar, so its molecules can stabilize both positive and negative ions through ion-dipole interactions.

Question 6

A reaction has a limiting reactant. Which of the following statements is true about the limiting reactant?

Accepted Answer

The limiting reactant is the one that determines the amount of product formed.

Question 7

Which of the following equations correctly represents the relationship between energy, frequency, and wavelength for electromagnetic radiation?

Accepted Answer

$$E = \frac{hc}{\lambda}$$

Question 8

Which of the following best describes the trend in atomic radius across a period from left to right in the periodic table?

Accepted Answer

Atomic radius decreases due to increasing effective nuclear charge.

Question 9

Which of the following molecules is nonpolar, despite having polar bonds?

Accepted Answer

$$\mathrm{CO}_2$$

Question 10

A sample of gas occupies 2.50 L at 1.00 atm and 300 K. What volume will it occupy at 2.00 atm and 300 K, assuming ideal behavior?

Accepted Answer

$$1.25\ \mathrm{L}$$

Question 11

Which of the following statements about hydrogen bonding is correct?

Accepted Answer

Hydrogen bonding occurs when hydrogen is bonded to highly electronegative atoms like N, O, or F.

Question 12

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

Accepted Answer

Ice is less dense than liquid water due to the open hexagonal structure formed by hydrogen bonds.

Question 13

Which of the following is the correct electron configuration for a ground-state phosphorus atom ($$Z=15$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^3$$

Question 14

Which of the following best describes the effect of increasing temperature on the vapor pressure of a liquid?

Accepted Answer

Vapor pressure increases as temperature increases.

Question 15

A reaction releases 250 J of heat and does 150 J of work on the surroundings. What is the change in internal energy ($$\Delta E) of $$the system?

Accepted Answer

$$\Delta E = -100\ \mathrm{J}$$

Question 16

Which of the following best explains why real gases deviate from ideal behavior at high pressures?

Accepted Answer

At high pressures, the volume of gas particles becomes significant and intermolecular forces become important.

Question 17

Which of the following is the correct Lewis structure for the nitrate ion ($$\mathrm{NO}_3^-$$)?

Accepted Answer

A structure with one N–O double bond and two N–O single bonds, with resonance among the three oxygens.

Question 18

Which of the following molecules has a trigonal planar molecular geometry?

Accepted Answer

$$\mathrm{BF}_3$$

Question 19

Which of the following statements about molecular orbital (MO) theory is correct?

Accepted Answer

Bond order can be calculated as $$\frac{1}{2}(	ext{number of bonding electrons} - 	ext{number of antibonding electrons}).$$

Question 20

A solution is prepared by dissolving 5.00 g of NaCl in enough water to make 250.0 mL of solution. What is the molarity of the solution? ($$\mathrm{NaCl}$$ molar mass = 58.44 g/mol)

Accepted Answer

$$0.342\ \mathrm{M}$$

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