Q: A 200.0 mg tablet of ibuprofen (C$$_{13}H$_{18}O$_2) is $$analyzed. How many molecules of ibuprofen are present in the tablet? (Molar mass = 206.29 g/mol, Avogadro's number = $$6.022 \times 10$$^{23}$$)

$$\frac{0.2000}{206.29} \times 6.022 \times 10$$^{23}$$ = 5.84 \times 10$$^{20}$$ molecules

Q: What is the mass percent of chlorine in Freon-112 ($$\mathrm{C}_2\mathrm{Cl}_4\mathrm{F}_2$$)? (Atomic masses: C = 12.01, Cl = 35.45, F = 19.00)

$$\frac{4 \times 35.45}{2 \times 12.01 + 4 \times 35.45 + 2 \times 19.00} \times 100 = 58.64\%$$

Question 1

Which of the following statements best explains why water (H$$_2O) is $$considered a compound and not a mixture?

Accepted Answer

Water is composed of two hydrogen atoms and one oxygen atom in a fixed ratio.

Question 2

Which type of chemical bond is formed when electrons are transferred from a metal to a nonmetal?

Accepted Answer

Ionic bond

Question 3

What is the empirical formula for a compound with the molecular formula C$$_6H$_{12}O$_6$$?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 4

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

Accepted Answer

An empirical formula shows the simplest whole-number ratio of atoms, while a molecular formula shows the actual number of atoms of each element.

Question 5

Which of the following compounds contains a type two cation (a metal with variable charge)?

Accepted Answer

$$\mathrm{FeCl}_3$$

Question 6

What is the correct name for the compound $$\mathrm{CuSO}_4 \cdot 5\mathrm{H}_2\mathrm{O}$$?

Accepted Answer

Copper(II) sulfate pentahydrate

Question 7

Which of the following best explains why ionic solids, such as NaCl, conduct electricity when dissolved in water but not in the solid state?

Accepted Answer

The ions are locked in place in the solid state but can move freely when dissolved, allowing electrical conductivity.

Question 8

Calculate the formula mass of calcium nitrate, $$\mathrm{Ca(NO}_3)_2. ($$Atomic masses: Ca = 40.08, N = 14.01, O = 16.00)

Accepted Answer

$$40.08 + 2(14.01) + 6(16.00) = 164.10 g/$$mol

Question 9

A sample of a compound contains 24.5 g of nitrogen and 70.0 g of oxygen. What is the empirical formula of the compound? (Atomic masses: N = 14.01, O = 16.00)

Accepted Answer

$$\mathrm{N}_2\mathrm{O}_5$$

Question 10

Which of the following statements about the octet rule is most accurate?

Accepted Answer

Atoms form bonds to lower their potential energy, and the octet rule helps predict when this will occur.

Question 11

Which of the following is the correct formula for the ionic compound formed between aluminum and nitrogen?

Accepted Answer

$$\mathrm{Al}_2\mathrm{N}_3$$

Question 12

Which of the following best describes a structural formula?

Accepted Answer

It shows how atoms are bonded to each other in a molecule using lines for bonds.

Question 13

A 200.0 mg tablet of ibuprofen (C$$_{13}H$_{18}O$_2) is $$analyzed. How many molecules of ibuprofen are present in the tablet? (Molar mass = 206.29 g/mol, Avogadro's number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$\frac{0.2000}{206.29} 	imes 6.022 	imes 10$$^{23}$$ = 5.84 	imes 10$$^{20}$$ molecules

Question 14

Which of the following is the correct name for the compound P$$_2O$_5$$?

Accepted Answer

Diphosphorus pentoxide

Question 15

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

Accepted Answer

MgO has ions with larger charges, leading to stronger electrostatic attraction.

Question 16

What is the mass percent of chlorine in Freon-112 ($$\mathrm{C}_2\mathrm{Cl}_4\mathrm{F}_2$$)? (Atomic masses: C = 12.01, Cl = 35.45, F = 19.00)

Accepted Answer

$$\frac{4 	imes 35.45}{2 	imes 12.01 + 4 	imes 35.45 + 2 	imes 19.00} 	imes 100 = 58.64\%$$

Question 17

Which of the following is a correct ratio derived from the molecular formula for water ($$\mathrm{H}_2\mathrm{O}$$)?

Accepted Answer

$$\frac{2\ 	ext{mol H}}{1\ 	ext{mol O}}$$

Question 18

A compound has an empirical formula of CH$$_2O $$and a molar mass of 180.16 g/mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$$

Question 19

Which of the following best describes why carbon is the central element in organic chemistry?

Accepted Answer

Carbon can form four covalent bonds and create chains and rings of unlimited length.

Chapter 4: Molecules and Compounds – Structure, Bonding, and Chemical Formulas

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