Q: How many molecules are present in 18.0 g of water ($$\mathrm{H_2O}$$)? ($$\mathrm{M_{H_2O}} = 18.0\ \mathrm{g/mol}$$, $$N_A = 6.022 \times 10$$^{23}$$\ \mathrm{mol}^{-1})$$

$$6.022 \times 10$$^{23}$$ molecules

Question 1

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

Accepted Answer

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

Question 2

A sample of a compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 3

Which of the following statements about ionic and covalent bonds is correct?

Accepted Answer

Ionic bonds involve the transfer of electrons from one atom to another, while covalent bonds involve the sharing of electrons between atoms.

Question 4

Which of the following compounds is named correctly?

Accepted Answer

Sodium sulfate: $$\mathrm{Na_2SO_4}$$

Question 5

What is the molar mass of $$\mathrm{Ca(OH)_2}$$?

Accepted Answer

$$74.09\ \mathrm{g/mol}$$

Question 6

How many molecules are present in 18.0 g of water ($$\mathrm{H_2O}$$)? ($$\mathrm{M_{H_2O}} = 18.0\ \mathrm{g/mol}$$, $$N_A = 6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1})$$

Accepted Answer

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

Question 7

Which of the following elements has the highest first ionization energy?

Accepted Answer

Neon ($$\mathrm{Ne})$$

Question 8

Which of the following is the correct electron configuration for the $$\mathrm{O$$^{2-}$$}$$ ion?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$

Question 9

Which of the following statements about periodic trends is correct?

Accepted Answer

Atomic radius decreases across a period from left to right.

Question 10

Which of the following Lewis structures is most likely for the nitrate ion ($$\mathrm{NO_3$^-}$$)?

Accepted Answer

Three resonance structures, each with one N=O double bond and two N–O single bonds, with a negative charge delocalized over the three oxygens.

Question 11

Which of the following bonds is both the strongest and the shortest?

Accepted Answer

Covalent triple bond

Question 12

What is the formal charge on the central atom in the best Lewis structure for $$\mathrm{SO_2$}$$?

Accepted Answer

0

Question 13

Which of the following best describes electronegativity?

Accepted Answer

The ability of an atom in a molecule to attract shared electrons to itself.

Question 14

Which of the following compounds contains both ionic and covalent bonds?

Accepted Answer

$$\mathrm{$$NaNO_3$$}$$

Question 15

A compound has a molar mass of $$58.12\ \mathrm{g/mol}$$ and an empirical formula of $$\mathrm{C_2H_5}. $$What is its molecular formula?

Accepted Answer

$$\mathrm{C_4H_{10}}$$

Question 16

Which of the following sets of quantum numbers is NOT allowed for an electron in an atom?

Accepted Answer

$$n=2,\ l=2,\ m_l=0,\ m_s=+\frac{1}{2}$$

Question 17

Which of the following statements about bond energy and bond length is correct?

Accepted Answer

Shorter bonds are generally stronger and have higher bond energies.

Question 18

How many valence electrons are present in a molecule of $$\mathrm{CO_2$}$$?

Accepted Answer

16

Question 19

Which of the following best explains why $$\mathrm{Mg$$^{2+}$$} is $$smaller than $$\mathrm{Mg}$$?

Accepted Answer

Loss of two electrons reduces electron-electron repulsion and results in a smaller ionic radius.

Question 20

A 10.0 g sample of a compound contains 4.0 g of carbon, 0.67 g of hydrogen, and 5.33 g of oxygen. What is the mass percent of hydrogen in the compound?

Accepted Answer

$$6.7\%$$

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