Q: What is the mass percent of oxygen in $\mathrm{CO_2}$? (Atomic masses: C = 12.0 g/mol, O = 16.0 g/mol)

$\displaystyle \frac{32.0}{44.0} \times 100\% = 72.7\%$

Q: What is the formula mass of $\mathrm{Al_2(SO_4)_3}$? (Atomic masses: Al = 27.0 g/mol, S = 32.1 g/mol, O = 16.0 g/mol)

$2 \times 27.0 + 3 \times 32.1 + 12 \times 16.0 = 342.2\ \mathrm{g/mol}$

Question 1

Which of the following best explains why MgO has a higher melting point than NaCl?

Accepted Answer

Because MgO has ions with higher charges ($\mathrm{Mg^{2+}}$ and $\mathrm{O^{2-}}$), resulting in stronger electrostatic forces than the $\mathrm{Na^+}$ and $\mathrm{Cl^-}$ ions in NaCl.

Question 2

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

Accepted Answer

$\mathrm{CH_2O}$

Question 3

Which of the following statements about ionic and molecular compounds is correct?

Accepted Answer

Ionic compounds form crystalline solids at room temperature, while molecular compounds can exist as gases, liquids, or solids.

Question 4

What is the correct name for the compound $\mathrm{Fe_2O_3}$?

Accepted Answer

Iron(III) oxide

Question 5

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by the sharing of electron pairs between atoms.

Question 6

A sample of a compound contains 0.600 mol of carbon, 1.20 mol of hydrogen, and 0.600 mol of oxygen. What is the empirical formula of the compound?

Accepted Answer

$\mathrm{CH_2O}$

Question 7

Which of the following is the correct formula for calcium phosphate?

Accepted Answer

$\mathrm{Ca_3(PO_4)_2}$

Question 8

What is the mass percent of oxygen in $\mathrm{CO_2}$? (Atomic masses: C = 12.0 g/mol, O = 16.0 g/mol)

Accepted Answer

$\displaystyle \frac{32.0}{44.0} 	imes 100\% = 72.7\%$

Question 9

Which of the following compounds is a molecular compound?

Accepted Answer

$\mathrm{CO_2}$

Question 10

A hydrated ionic compound has the formula $\mathrm{CuSO_4 \cdot 5H_2O}$. What is the correct name for this compound?

Accepted Answer

Copper(II) sulfate pentahydrate

Question 11

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

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms in a compound, while the molecular formula shows the actual number of atoms of each element in a molecule.

Question 12

Which of the following is the correct Lewis symbol for sulfur?

Accepted Answer

$\mathrm{S}$ with 6 dots around it

Question 13

What is the formula mass of $\mathrm{Al_2(SO_4)_3}$? (Atomic masses: Al = 27.0 g/mol, S = 32.1 g/mol, O = 16.0 g/mol)

Accepted Answer

$2 	imes 27.0 + 3 	imes 32.1 + 12 	imes 16.0 = 342.2\ \mathrm{g/mol}$

Question 14

Which of the following is the correct name for $\mathrm{N_2O_5}$?

Accepted Answer

Dinitrogen pentoxide

Question 15

A 10.0 g sample of $\mathrm{CO_2}$ contains how many molecules? (Molar mass of $\mathrm{CO_2}$ = 44.0 g/mol, Avogadro's number $= 6.022 	imes 10^{23}$ molecules/mol)

Accepted Answer

$\displaystyle \frac{10.0\ \mathrm{g}}{44.0\ \mathrm{g/mol}} 	imes 6.022 	imes 10^{23} = 1.37 	imes 10^{23}$ molecules

Question 16

Which of the following is a correct statement about polyatomic ions?

Accepted Answer

Polyatomic ions are composed of two or more atoms covalently bonded, carrying a net charge.

Question 17

Which of the following best describes the process of combustion analysis?

Accepted Answer

It is used to determine the empirical formula of a compound by burning the sample and measuring the amounts of $\mathrm{CO_2}$ and $\mathrm{H_2O}$ produced.

Question 18

Which of the following is the correct formula for ammonium sulfate?

Accepted Answer

$\mathrm{(NH_4)_2SO_4}$

Question 19

Which of the following statements about the octet rule is correct?

Accepted Answer

Atoms tend to gain, lose, or share electrons to achieve a total of eight valence electrons.

Chapter 4: Molecules and Compounds

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