Q: What is the percent by mass of oxygen in $$\mathrm{H_2SO_4}$$? (Molar mass: $$\mathrm{H_2SO_4} = 98\ \mathrm{g\cdot $$mol^{-1}$$})$$

$$\displaystyle \frac{64}{98} \times 100 = 65.3\%$$

Question 1

Which of the following best explains why the second ionization energy of sodium ($$\mathrm{Na}) is $$much greater than its first ionization energy?

Accepted Answer

The second electron is removed from a completely filled shell, which is more stable.

Question 2

Which of the following compounds is most likely to be ionic?

Accepted Answer

$$\mathrm{NaCl}$$

Question 3

Given the following ions: ammonium ($$\mathrm{NH_4$^+}$$), hydroxide ($$\mathrm{OH^-}$$), carbonate ($$\mathrm{CO_3$^{2-}}$$), and nitrate ($$\mathrm{NO_3$^-}$$), which formula represents ammonium carbonate?

Accepted Answer

$$\mathrm{(NH_4$)_2CO_3}$$

Question 4

Which of the following best describes why bond formation is an exothermic process?

Accepted Answer

Energy is released as atoms achieve a more stable, lower energy state when bonds form.

Question 5

A molecule has the empirical formula $$\mathrm{CH_2O}$$ and a molar mass of $$180\ \mathrm{g\cdot $$mol^{-1}$$}. $$What is its molecular formula?

Accepted Answer

$$\mathrm{C_6H_{12}O_6$}$$

Question 6

Which of the following statements about electronegativity and bond polarity is correct?

Accepted Answer

A bond between atoms with a large difference in electronegativity will be more polar.

Question 7

Which of the following best explains why ozone ($$\mathrm{O_3$}) $$can absorb UV-B radiation while $$\mathrm{O_2$}$$ cannot?

Accepted Answer

Ozone has resonance structures that allow it to absorb UV-B radiation.

Question 8

What is the formal charge on the central atom in the Lewis structure of $$\mathrm{NO_3$^-} ($$nitrate ion)?

Accepted Answer

0

Question 9

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

Accepted Answer

$$\mathrm{CO_2$}$$

Question 10

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

Accepted Answer

$$\sigma$$ bonds result from head-on overlap of orbitals, while $$\pi$$ bonds result from side-on overlap.

Question 11

A molecule has a central atom with three bonding pairs and one lone pair. What is its molecular geometry according to VSEPR theory?

Accepted Answer

Trigonal pyramidal

Question 12

Which of the following best explains why $$\mathrm{He_2$}$$ does not exist as a stable molecule, according to molecular orbital theory?

Accepted Answer

The number of electrons in bonding and antibonding orbitals is equal, resulting in no net bond.

Question 13

Which of the following is the correct name for $$\mathrm{$$FeCl_3$$}$$?

Accepted Answer

Iron(III) chloride

Question 14

What is the percent by mass of oxygen in $$\mathrm{H_2SO_4}$$? (Molar mass: $$\mathrm{H_2SO_4} = 98\ \mathrm{g\cdot $$mol^{-1}$$})$$

Accepted Answer

$$\displaystyle \frac{64}{98} 	imes 100 = 65.3\%$$

Question 15

Which hybridization is present in the central carbon atom of $$\mathrm{CO_2$}$$?

Accepted Answer

$$sp$$

Question 16

Which of the following best describes the concept of resonance in Lewis structures?

Accepted Answer

Resonance is the delocalization of electrons across multiple valid Lewis structures.

Question 17

How many sigma ($$\sigma) $$and pi ($$\pi) $$bonds are present in the molecule $$\mathrm{C_2H_2} ($$ethyne)?

Accepted Answer

3 $$\sigma$$ bonds and 2 $$\pi$$ bonds

Question 18

Which of the following is a correct statement about cis- and trans- isomers?

Accepted Answer

Cis- and trans- isomers arise due to restricted rotation around double bonds.

Question 19

Which of the following best describes the role of constructive interference in chemical bonding?

Accepted Answer

Constructive interference increases electron density between nuclei, stabilizing the bond.

Question 20

A sample contains $$18\ \mathrm{g} of $$water ($$\mathrm{H_2O}). $$How many molecules of water are present? ($$\mathrm{M_{H_2O}} = 18\ \mathrm{g\cdot $$mol^{-1}$$}$$, $$N_A = 6.022 	imes 10$$^{23}$$\ \mathrm{$$mol^{-1}$$})$$

Accepted Answer

$$6.022 	imes 10$$^{23}$$ molecules

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