Q: Which of the following statements best describes a mole in chemistry?

A mole is the amount of a substance that contains $$6.022 \times 10$$^{23}$$ entities.

Q: Which equation correctly relates the number of entities to the amount in moles?

$$\text{No. of entities} = n \times N_A$$

Q: Which of the following is the correct formula for calculating mass percent of an element X in a compound?

$$\text{Mass \% of X} = \frac{\text{Moles of X in formula} \times \text{Molar mass of X}}{\text{Mass of 1 mol of compound}} \times 100\%$$

Question 1

Which of the following statements best describes a mole in chemistry?

Accepted Answer

A mole is the amount of a substance that contains $$6.022 	imes 10$$^{23}$$ entities.

Question 2

How many oxygen atoms are present in 41.6 g of ammonium carbonate ($$\mathrm{(NH_4$)_2CO_3}$$)? (Molar mass = 96.09 g/mol)

Accepted Answer

$$7.83 	imes 10$$^{23}$$

Question 3

A sample contains 5.08 g of Zn, 1.60 g of P, and 3.32 g of O. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{Zn_3P_2O_8}$$

Question 4

Which equation correctly relates the number of entities to the amount in moles?

Accepted Answer

$$	ext{No. of entities} = n 	imes N_A$$

Question 5

A 1.000 g sample of vitamin C produces 1.50 g of $$\mathrm{CO_2$}$$ and 0.41 g of $$\mathrm{H_2O}$$ upon combustion. If the molar mass of vitamin C is 176.12 g/mol, what is its molecular formula?

Accepted Answer

$$\mathrm{C_6H_8O_6}$$

Question 6

What is the mass percent of nitrogen in ammonium nitrate ($$\mathrm{NH_4NO_3}$$)? (Molar mass = 80.05 g/mol)

Accepted Answer

35.00%

Question 7

If 0.0342 mol of Ag is used in jewelry, how many grams of Ag does this represent? (Molar mass of Ag = 107.87 g/mol)

Accepted Answer

3.69 g

Question 8

Which of the following best describes the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed first, limiting the amount of product formed.

Question 9

A fuel mixture contains 100 g of $$\mathrm{N_2H_4}$$ and 125 g of $$\mathrm{N_2O_4}. $$The reaction is $$2\mathrm{N_2H_4} + \mathrm{N_2O_4} \rightarrow 3\mathrm{N_2$} + 4\mathrm{H_2O}. $$What is the mass of nitrogen gas produced?

Accepted Answer

114 g

Question 10

What is the percent yield if 51.4 kg of SiC is recovered from processing 100.0 kg of $$\mathrm{$$SiO_2$$}$$? (Molar mass $$\mathrm{$$SiO_2$$} = 60.08 g/$$mol, $$\mathrm{SiC} = 40.09 g/$$mol)

Accepted Answer

77.0%

Question 11

Which of the following is the correct balanced equation for the combustion of octane ($$\mathrm{C_8H_{18}}$$)?

Accepted Answer

$$2\mathrm{C_8H_{18}} + 25\mathrm{O_2$} \rightarrow 16\mathrm{CO_2$} + 18\mathrm{H_2O}$$

Question 12

How many moles of $$\mathrm{O_2$}$$ are required to roast 10.0 mol of $$\mathrm{Cu_2S}$$ according to the reaction $$2\mathrm{Cu_2S} + 3\mathrm{O_2$} \rightarrow 2\mathrm{Cu_2O} + 2\mathrm{SO_2$}$$?

Accepted Answer

15.0 mol

Question 13

Which of the following is the correct formula for calculating mass percent of an element X in a compound?

Accepted Answer

$$	ext{Mass \% of X} = \frac{	ext{Moles of X in formula} 	imes 	ext{Molar mass of X}}{	ext{Mass of 1 mol of compound}} 	imes 100\%$$

Question 14

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

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

Question 15

Which of the following best describes the difference between empirical and molecular formulas?

Accepted Answer

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

Question 16

If you have 95.8 g of Fe, how many Fe atoms are present? (Molar mass of Fe = 55.85 g/mol, $$N_A = 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.04 	imes 10$$^{24}$$

Question 17

Which of the following is a correct step in balancing a chemical equation?

Accepted Answer

Adjust the coefficients to obtain the smallest whole numbers.

Stoichiometry of Formulas and Equations: The Mole, Chemical Formulas, and Reaction Calculations

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