Q: A sample contains 3.0 moles of $$\ce{NaCl}. $$How many formula units are present in the sample? ($$N_A = 6.022 \times 10$$^{23}$$\ \text{mol}^{-1})$$

$$1.81 \times 10$$^{24}$$ formula units

Q: Which of the following is the correct formula for calculating the percent yield of a reaction?

$$\text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$$

Question 1

Which of the following best describes the difference between a chemical property and a physical property of matter?

Accepted Answer

A chemical property describes the ability of a substance to undergo a specific chemical change, while a physical property can be observed without changing the substance's identity.

Question 2

A student measures the mass of a sample as 12.345 g. If the balance used has a precision of 0.01 g, how should the student properly report the measurement?

Accepted Answer

Question 3

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

Accepted Answer

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

Question 4

A sample contains 3.0 moles of $$\ce{NaCl}. $$How many formula units are present in the sample? ($$N_A = 6.022 	imes 10$$^{23}$$\ 	ext{mol}^{-1})$$

Accepted Answer

$$1.81 	imes 10$$^{24}$$ formula units

Question 5

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

Accepted Answer

Elements in the same group have the same number of valence electrons.

Question 6

Which of the following compounds is named correctly?

Accepted Answer

NaCl: sodium chloride

Question 7

A reaction has the following balanced equation: $$2\ce{H_2$} + \ce{O_2$} \rightarrow 2\ce{H_2O}. If $$you start with 4.0 mol $$\ce{H_2$}$$ and 2.0 mol $$\ce{O_2$}$$, what is the limiting reagent?

Accepted Answer

Neither, both are in excess

Question 8

Which of the following is a correct net ionic equation for the reaction between aqueous solutions of silver nitrate and sodium chloride?

Accepted Answer

$$\ce{Ag^+ (aq) + Cl^- (aq) \rightarrow AgCl (s)}$$

Question 9

A gas occupies 10.0 L at 2.00 atm and 300 K. What volume will it occupy at 1.00 atm and 300 K? (Assume ideal gas behavior.)

Accepted Answer

20.0 L

Question 10

Which of the following statements about the First Law of Thermodynamics is correct?

Accepted Answer

Energy is conserved; it can be transferred or transformed but not created or destroyed.

Question 11

Which of the following Lewis structures is correct for carbon dioxide ($$\ce{CO_2$}$$)?

Accepted Answer

O=C=O, with each O atom having two lone pairs

Question 12

Which molecular geometry is predicted by VSEPR theory for $$\ce{NH_3$}$$?

Accepted Answer

Trigonal pyramidal

Question 13

Which of the following intermolecular forces is strongest in liquid water?

Accepted Answer

Hydrogen bonding

Question 14

A sample of gas is collected over water at 25°C. The total pressure is 755 mmHg, and the vapor pressure of water at 25°C is 23.8 mmHg. What is the partial pressure of the dry gas?

Accepted Answer

731.2 mmHg

Question 15

Which of the following best explains why ionic compounds tend to have high melting points?

Accepted Answer

Strong electrostatic forces between oppositely charged ions require a large amount of energy to break.

Question 16

Which of the following is the correct formula for calculating the percent yield of a reaction?

Accepted Answer

$$	ext{Percent Yield} = \frac{	ext{Actual Yield}}{	ext{Theoretical Yield}} 	imes 100\%$$

Question 17

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

Accepted Answer

Molecular compounds are formed from nonmetals sharing electrons, while ionic compounds are formed from metals and nonmetals transferring electrons.

Question 18

Which of the following is a correct application of Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the same, regardless of the number of steps in the reaction.

Question 19

Which of the following best describes the relationship between vapor pressure and boiling point?

Accepted Answer

A liquid boils when its vapor pressure equals the external pressure.

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