Q: Which equation correctly relates mass, moles, and molar mass?

$$\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$$

Question 1

According to the Law of Conservation of Mass, what must be true for any chemical reaction?

Accepted Answer

The total mass of the reactants is equal to the total mass of the products.

Question 2

Given the balanced equation $$4Fe(s) + 3O_2(g) \rightarrow 2Fe_2O_3(s)$$, how many moles of $$Fe$$ are required to react with $$12.0$$ moles of $$O_2$$?

Accepted Answer

$$16.0$$ moles

Question 3

Which of the following is a correct mole-mole factor for the reaction $$3H_2(g) + N_2$(g) \rightarrow 2NH_3(g)$$?

Accepted Answer

$$\frac{2\ moles\ NH_3$}{3\ moles\ H_2$}$$

Question 4

If $$45.8 g of$$ $$Fe_2O_3 is $$produced, how many grams of $$O_2$$ are needed? (Molar masses: $$Fe_2O_3 = 159.7 g/$$mol, $$O_2 = 32.0$ g/mol; reaction: 4Fe(s) + 3O_2(g$$) \rightarrow 2Fe_2O_3(s)$$)

Accepted Answer

$$13.7 g$$

Question 5

A reaction between $$2Ag(s)$$ and $$S(s)$$ produces $$Ag_2S(s). If $$you start with $$2.159 g of$$ $$Ag$$ and $$0.321 g of$$ $$S$$, what is the expected mass of $$Ag_2S$$ produced?

Accepted Answer

$$2.480 g$$

Question 6

Which step is NOT necessary when calculating the mass of a product from the mass of a reactant in a chemical reaction?

Accepted Answer

Directly multiplying the mass of reactant by the mass of product.

Question 7

In the reaction $$2Fe(s) + 3S(s) \rightarrow Fe_2S_3(s)$$, what is the mole-mole factor between $$Fe$$ and $$S$$?

Accepted Answer

$$\frac{3\ moles\ S}{2\ moles\ Fe}$$

Question 8

A student wants to produce $$13.1 g of$$ $$H_2O$$ using $$O_2. $$How many grams of $$O_2$$ are required? (Molar masses: $$H_2O = 18.0 g/$$mol, $$O_2 = 32.0$ g/mol; reaction: 2H_2(g$$) + $$O_2(g$$) \rightarrow 2H_2O(g)$$)

Accepted Answer

$$5.82 g$$

Question 9

Which equation correctly relates mass, moles, and molar mass?

Accepted Answer

$$	ext{Moles} = \frac{	ext{Mass (g)}}{	ext{Molar Mass (g/mol)}}$$

Question 10

If $$3.0$$ moles of $$N_2$$ react with excess $$H_2$$ according to $$3H_2(g) + N_2$(g) \rightarrow 2NH_3(g)$$, how many moles of $$NH_3$$ are produced?

Accepted Answer

$$6.0$$ moles

Question 11

Which of the following best describes the purpose of using a mole-mole factor in stoichiometric calculations?

Accepted Answer

To convert between the amounts of different substances in a reaction using the coefficients from the balanced equation.

Question 12

A reaction produces $$2.480 g of$$ $$Ag_2S$$ from $$2.159 g of$$ $$Ag$$ and $$0.321 g of$$ $$S. $$What does this demonstrate about the Law of Conservation of Mass?

Accepted Answer

The total mass of reactants equals the total mass of products.

Question 13

Which of the following is the correct sequence for solving a mass-to-mass stoichiometry problem?

Accepted Answer

Mass A $$\rightarrow$$ Moles A $$\rightarrow$$ Moles B $$\rightarrow$$ Mass B

Question 14

If $$4.0$$ moles of $$Fe$$ react with $$3.0$$ moles of $$S$$ according to $$2Fe(s) + 3S(s) \rightarrow Fe_2S_3(s)$$, which reactant is the limiting reagent?

Accepted Answer

$$S$$

Question 15

In a laboratory, a student mixes $$2.0$$ moles of $$H_2$$ with $$1.0$$ mole of $$O_2 to $$produce water. According to $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(g)$$, how many moles of water can be formed?

Accepted Answer

$$2.0$$ moles

Question 16

Which of the following is NOT a correct mole-mole factor for the reaction $$2Fe(s) + 3S(s) \rightarrow Fe_2S_3(s)$$?

Accepted Answer

$$\frac{2\ moles\ Fe}{1\ mole\ Fe_2S_3}$$

Mole and Mass Calculations in Chemical Reactions

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