Q: A sample of $$\mathrm{C}_2\mathrm{H}_6 ($$ethane) has a mass of $$30.0\ \mathrm{g}. $$How many molecules of ethane are present in the sample? (Molar mass of $$\mathrm{C}_2\mathrm{H}_6 = 30.07\ \mathrm{g/mol})$$

$$6.02 \times 10$$^{23}$$ molecules

Question 1

Which of the following statements best describes the difference between ionic and covalent bonds?

Accepted Answer

Ionic bonds involve the transfer of electrons from a metal to a nonmetal, resulting in oppositely charged ions, while covalent bonds involve the sharing of electrons between two nonmetals.

Question 2

Which of the following compounds is expected to have the highest lattice energy?

Accepted Answer

$$\mathrm{MgO}$$

Question 3

Given the following percent composition by mass: 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen, what is the empirical formula of the compound?

Accepted Answer

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

Question 4

Which of the following molecules is nonpolar, despite having polar bonds?

Accepted Answer

$$\mathrm{CO}_2$$

Question 5

What is the formal charge on the nitrogen atom in the nitrate ion, $$\mathrm{NO}_3^-$$, if the Lewis structure has one double bond and two single bonds to oxygen atoms?

Accepted Answer

$$0$$

Question 6

Which of the following best explains why $$\mathrm{O}_2 is $$paramagnetic?

Accepted Answer

Because it has unpaired electrons in its molecular orbitals.

Question 7

A sample of $$\mathrm{C}_2\mathrm{H}_6 ($$ethane) has a mass of $$30.0\ \mathrm{g}. $$How many molecules of ethane are present in the sample? (Molar mass of $$\mathrm{C}_2\mathrm{H}_6 = 30.07\ \mathrm{g/mol})$$

Accepted Answer

$$6.02 	imes 10$$^{23}$$ molecules

Question 8

Which of the following statements about resonance structures is correct?

Accepted Answer

The true structure of a molecule is a hybrid of all valid resonance structures.

Question 9

What is the hybridization of the central atom in $$\mathrm{SF}_4$$?

Accepted Answer

$$\mathrm{sp}^3\mathrm{d}$$

Question 10

Which of the following best describes the geometry and bond angles of $$\mathrm{NH}_3$$ according to VSEPR theory?

Accepted Answer

Trigonal pyramidal geometry, approximately $$107^\circ$$ bond angles

Question 11

A reaction has a theoretical yield of $$10.0\ \mathrm{g}$$, but only $$7.5\ \mathrm{g} of $$product is actually obtained. What is the percent yield?

Accepted Answer

$$75\%$$

Question 12

Which of the following is the correct name for $$\mathrm{FeCl}_3$$?

Accepted Answer

Iron(III) chloride

Question 13

Which of the following is a correct Lewis structure for $$\mathrm{CO}_3$$^{2-}$$ (carbonate ion)?

Accepted Answer

A structure with one double bond and two single bonds to oxygen, with all oxygens having a full octet and a formal charge of $$-1 on $$two oxygens.

Question 14

Which of the following best describes the difference between sigma ($$\sigma) $$and pi ($$\pi) $$bonds?

Accepted Answer

$$\sigma$$ bonds are stronger than $$\pi$$ bonds and are formed by end-to-end overlap, while $$\pi$$ bonds are formed by side-to-side overlap.

Question 15

Which of the following is the correct formula for the compound formed between potassium and phosphate?

Accepted Answer

$$\mathrm{K}_3\mathrm{PO}_4$$

Question 16

A chemical reaction is carried out with $$5.00\ \mathrm{g} of$$ $$\mathrm{Al}$$ and $$10.0\ \mathrm{g} of$$ $$\mathrm{Cl}_2$$ according to the equation: $$2\mathrm{Al} + 3\mathrm{Cl}_2 \rightarrow 2\mathrm{AlCl}_3. $$Which reactant is the limiting reactant? (Molar masses: $$\mathrm{Al} = 26.98\ \mathrm{g/mol}$$, $$\mathrm{Cl}_2 = 70.90\ \mathrm{g/mol})$$

Accepted Answer

$$\mathrm{Cl}_2$$

Question 17

Which of the following best describes the trend in electronegativity across a period in the periodic table?

Accepted Answer

Electronegativity increases from left to right.

Question 18

Which of the following is the correct molecular formula for a compound with an empirical formula of $$\mathrm{CH}_2\mathrm{O}$$ and a molar mass of $$180\ \mathrm{g/mol}$$?

Accepted Answer

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

Question 19

Which of the following best explains why $$\mathrm{H}_2\mathrm{O}$$ has a bent molecular geometry?

Accepted Answer

Because lone pairs on the oxygen atom repel the bonding pairs, resulting in a bent shape.

Question 20

Which of the following is a correct balanced chemical equation for the combustion of propane ($$\mathrm{C}_3\mathrm{H}_8$$)?

Accepted Answer

$$\mathrm{C}_3\mathrm{H}_8 + 5\mathrm{O}_2 \rightarrow 3\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O}$$

Exam 2 Study Guide: Chemical Bonding, Compounds, and Chemical Reactions

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