Q: A sample of sodium chloride (NaCl) contains 39% sodium by mass. If a person consumes 2.4 g of sodium, what is the minimum mass of NaCl they have ingested?

$$2.4\ \mathrm{g} \times \frac{100}{39} = 6.2\ \mathrm{g}$$

Q: What is the mass percent of chlorine in CCl$$_2F$_2$$? (Given: molar mass of Cl = 35.45 g/mol, molar mass of CCl$$_2F$_2 = 120.91 g/$$mol)

$$\frac{2 \times 35.45}{120.91} \times 100\% = 58.64\%$$

Q: Which of the following is the correct formula for calculating the mass percent of an element X in a compound?

$$\frac{\text{mass of element X in 1 mol of compound}}{\text{mass of 1 mol of compound}} \times 100\%$$

Question 1

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

Accepted Answer

Ionic compounds are formed by transferring electrons from a metal to a nonmetal, while covalent compounds are formed by sharing electrons between two nonmetals.

Question 2

Which of the following is the empirical formula for the compound with the molecular formula $$\mathrm{C}_4\mathrm{H}_8$$?

Accepted Answer

$$\mathrm{CH}_2$$

Question 3

A sample of sodium chloride (NaCl) contains 39% sodium by mass. If a person consumes 2.4 g of sodium, what is the minimum mass of NaCl they have ingested?

Accepted Answer

$$2.4\ \mathrm{g} 	imes \frac{100}{39} = 6.2\ \mathrm{g}$$

Question 4

Which of the following substances is a molecular element?

Accepted Answer

O$$_2$$

Question 5

What is the mass percent of chlorine in CCl$$_2F$_2$$? (Given: molar mass of Cl = 35.45 g/mol, molar mass of CCl$$_2F$_2 = 120.91 g/$$mol)

Accepted Answer

$$\frac{2 	imes 35.45}{120.91} 	imes 100\% = 58.64\%$$

Question 6

Which of the following best represents the structural formula for water?

Accepted Answer

H$$-O$-H$$

Question 7

A compound is found to contain 60.00% C, 4.48% H, and 35.52% O by mass. What is its empirical formula?

Accepted Answer

$$\mathrm{C}_3\mathrm{H}_4\mathrm{O}_2$$

Question 8

Which of the following is a polyatomic ion?

Accepted Answer

NO$$_3^-$$

Question 9

A 325 mg aspirin tablet contains acetylsalicylic acid (C$$_9H$_8O$_4). $$How many molecules of acetylsalicylic acid does it contain? (Molar mass = 180.15 g/mol, Avogadro's number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.09 	imes 10$$^{21}$$

Question 10

Which of the following best describes the process of combustion analysis for determining empirical formulas?

Accepted Answer

Burning a compound in oxygen and measuring the masses of CO$$_2$$ and H$$_2O $$produced to determine the amounts of C and H.

Question 11

Which of the following is the correct order of elements in C$$_6H$_8O in $$decreasing mass percent composition?

Accepted Answer

O \u003e C \u003e H

Question 12

Which of the following is the correct molecular formula for a compound with an empirical formula of CH and a molar mass of 78.11 g/mol? (Empirical formula mass = 13.02 g/mol)

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_6$$

Question 13

Which of the following best describes a formula unit?

Accepted Answer

The smallest, electrically neutral collection of ions in an ionic compound.

Question 14

Which of the following is a correct statement about chemical formulas?

Accepted Answer

Chemical formulas list the more metallic element first, followed by the less metallic element.

Question 15

Which of the following is a diatomic molecule?

Accepted Answer

O$$_2$$

Question 16

Which of the following best describes the difference between a molecular formula and an empirical formula?

Accepted Answer

A molecular formula gives the actual number of atoms of each element in a molecule, while an empirical formula gives the simplest whole-number ratio of atoms.

Question 17

Which of the following is the correct formula for calculating the mass percent of an element X in a compound?

Accepted Answer

$$\frac{	ext{mass of element X in 1 mol of compound}}{	ext{mass of 1 mol of compound}} 	imes 100\%$$

Molecules and Compounds: Types, Representation, and Quantitative Composition

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