Q: Calculate the formula mass of calcium hydroxide, Ca(OH)$$_2. ($$Atomic masses: Ca = 40.08, O = 16.00, H = 1.01)

$$40.08 + 2 \times (16.00 + 1.01) = 74.10$$

Q: How many carbon atoms are present in 0.40 mole of procaine, C$$_{13}H$_{20}N$_2O$_2$$?

$$0.40 \times 13 \times 6.022 \times 10$$^{23}$$ = 3.13 \times 10$$^{24}$$ atoms

Q: What is the percent by mass of oxygen in carbon dioxide (CO$$_2$$)? (Atomic masses: C = 12.01, O = 16.00)

$$\frac{2 \times 16.00}{12.01 + 2 \times 16.00} \times 100 = 72.7\%$$

Q: A sample of lead(II) chromate (PbCrO$$_4) is $$used as a pigment. What is the percent by mass of lead in PbCrO$$_4$$? (Atomic masses: Pb = 207.2, Cr = 52.00, O = 16.00)

$$\frac{207.2}{207.2 + 52.00 + 4 \times 16.00} \times 100 = 64.0\%$$

Question 1

Which of the following statements best describes an empirical formula?

Accepted Answer

It gives the relative numbers and types of atoms in a molecule, reduced to the simplest whole-number ratio.

Question 2

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

Accepted Answer

O$$_2$$

Question 3

A neutral atom that gains one or more electrons forms a(n) ________.

Accepted Answer

anion

Question 4

Which of the following best distinguishes an ionic compound from a molecular compound?

Accepted Answer

Ionic compounds consist of cations and anions held together by electrostatic forces.

Question 5

Calculate the formula mass of calcium hydroxide, Ca(OH)$$_2. ($$Atomic masses: Ca = 40.08, O = 16.00, H = 1.01)

Accepted Answer

$$40.08 + 2 	imes (16.00 + 1.01) = 74.10$$

Question 6

How many carbon atoms are present in 0.40 mole of procaine, C$$_{13}H$_{20}N$_2O$_2$$?

Accepted Answer

$$0.40 	imes 13 	imes 6.022 	imes 10$$^{23}$$ = 3.13 	imes 10$$^{24}$$ atoms

Question 7

Which of the following best describes a compound?

Accepted Answer

A substance consisting of two or more kinds of atoms chemically combined in a fixed ratio.

Question 8

What is the percent by mass of oxygen in carbon dioxide (CO$$_2$$)? (Atomic masses: C = 12.01, O = 16.00)

Accepted Answer

$$\frac{2 	imes 16.00}{12.01 + 2 	imes 16.00} 	imes 100 = 72.7\%$$

Question 9

If you have 50.0 g of CO$$_2$$, how many grams of oxygen are present? (Atomic masses: C = 12.01, O = 16.00)

Accepted Answer

$$50.0 	imes 0.727 = 36.4 g$$

Question 10

Which of the following is true about the relationship between formula mass and molar mass?

Accepted Answer

Formula mass and molar mass are numerically equal, but formula mass is in amu and molar mass is in g/mol.

Question 11

Which of the following best explains why empirical formulas are important in chemistry?

Accepted Answer

They provide the simplest whole-number ratio of atoms, which is useful for identifying unknown compounds.

Question 12

A sample of lead(II) chromate (PbCrO$$_4) is $$used as a pigment. What is the percent by mass of lead in PbCrO$$_4$$? (Atomic masses: Pb = 207.2, Cr = 52.00, O = 16.00)

Accepted Answer

$$\frac{207.2}{207.2 + 52.00 + 4 	imes 16.00} 	imes 100 = 64.0\%$$

Question 13

Which of the following is a correct statement about elements and compounds?

Accepted Answer

Compounds have properties different from the elements that compose them.

Question 14

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

Accepted Answer

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

Question 15

Which of the following is a property of ionic compounds?

Accepted Answer

They are generally composed of metals and nonmetals.

Question 16

A sample contains 0.25 mole of glucose (C$$_6H$_{12}O$_6). $$How many oxygen atoms are present?

Accepted Answer

$$0.25 	imes 6.022 	imes 10$$^{23}$$ 	imes 6 = 9.03 	imes 10$$^{23}$$ atoms

Question 17

Which of the following is NOT provided by a molecular formula?

Accepted Answer

The arrangement of atoms in space.

Question 18

Which of the following best describes a cation?

Accepted Answer

An atom or molecule that has lost one or more electrons.

Question 19

Which of the following is a correct way to calculate the percent composition of an element in a compound?

Accepted Answer

$$\frac{	ext{mass of element in 1 mole of compound}}{	ext{molar mass of compound}} 	imes 100$$

Molecules, Compounds, and Nomenclature: Chemical Formulas, Models, and Composition

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