Q: Which of the following is the correct percent composition by mass of oxygen in CO$_2$? (Atomic masses: C = 12.01, O = 16.00)

$\frac{32.00}{44.01} \times 100 = 72.7\%$

Question 1

Which of the following statements best explains why water (H$_2$O) has properties very different from its constituent elements, hydrogen and oxygen?

Accepted Answer

Water is a compound, and compounds have unique chemical and physical properties distinct from the elements that compose them.

Question 2

Which of the following is an example of a molecular compound?

Accepted Answer

CO$_2$

Question 3

What is the empirical formula for a compound with the molecular formula C$_6$H$_{12}$O$_6$?

Accepted Answer

CH$_2$O

Question 4

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

Accepted Answer

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

Question 5

Which of the following is the correct name for the compound Fe$_2$O$_3$?

Accepted Answer

Iron(III) oxide

Question 6

What is the correct chemical formula for copper(II) oxide?

Accepted Answer

CuO

Question 7

Which of the following is the correct name for the compound N$_2$O$_5$?

Accepted Answer

Dinitrogen pentoxide

Question 8

A sample contains 5.32 moles of CaCO$_3$. How many oxygen atoms are present in the sample?

Accepted Answer

$9.65 	imes 10^{24}$

Question 9

Which of the following is the correct name for the compound HNO$_2$(aq)?

Accepted Answer

Nitrous acid

Question 10

A hydrated ionic compound contains 6 waters of hydration per formula unit. Which of the following is the correct way to write the formula for cobalt(II) chloride hexahydrate?

Accepted Answer

CoCl$_2$ \cdot 6H$_2$O

Question 11

Which of the following is the correct percent composition by mass of oxygen in CO$_2$? (Atomic masses: C = 12.01, O = 16.00)

Accepted Answer

$\frac{32.00}{44.01} 	imes 100 = 72.7\%$

Question 12

A mineral contains 28.05% Mg, 21.85% Si, 1.16% H, and 48.94% O by mass. What is the mineral's empirical formula?

Accepted Answer

Mg$_2$SiO$_4$

Question 13

Which of the following is the correct molecular formula for a compound with empirical formula C$_2$H$_4$O and a molar mass of approximately 88 g/mol?

Accepted Answer

C$_4$H$_8$O$_2$

Question 14

Which of the following is NOT a correct name-formula pair?

Accepted Answer

Cu$_2$O is copper(II) oxide

Question 15

Which of the following is a polyatomic ion?

Accepted Answer

NO$_3^-$

Question 16

What is the correct name for the compound P$_2$O$_5$?

Accepted Answer

Diphosphorus pentoxide

Question 17

Which of the following is the correct formula for magnesium hydroxide?

Accepted Answer

Mg(OH)$_2$

Question 18

How many moles of hydrogen atoms are present in 50.0 g of methane (CH$_4$)? (Molar mass of CH$_4$ = 16.05 g/mol)

Accepted Answer

7.51 mol

Question 19

Which of the following best describes an oxyanion?

Accepted Answer

An anion containing oxygen and another element

Molecules and Compounds: Structure, Nomenclature, and Composition

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