Question 1

Which statement best describes the Law of Conservation of Mass as it applies to chemical reactions?

Accepted Answer

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

Question 2

In the reaction $$2\mathrm{Ag}(s) + \mathrm{S}(s) \rightarrow \mathrm{Ag}_2\mathrm{S}(s)$$, if you start with 215.8 g of Ag and 32.1 g of S, what is the total mass of Ag$$_2S $$produced?

Accepted Answer

$$247.9\ \mathrm{g}$$

Question 3

Which of the following is a correct mole–mole factor for the reaction $$2\mathrm{Fe}(s) + 3\mathrm{S}(s) \rightarrow \mathrm{Fe}_2\mathrm{S}_3(s)$$?

Accepted Answer

$$\frac{2\ \mathrm{mol}\ \mathrm{Fe}}{3\ \mathrm{mol}\ \mathrm{S}}$$

Question 4

How many moles of CO$$_2$$ are produced when 2.25 moles of C$$_3H$_8$$ react according to the equation $$\mathrm{C}_3\mathrm{H}_8(g) + 5\mathrm{O}_2(g) \rightarrow 3\mathrm{CO}_2(g) + 4\mathrm{H}_2\mathrm{O}(g)$$?

Accepted Answer

$$6.75\ \mathrm{mol}$$

Question 5

A welder uses acetylene ($$\mathrm{C}_2\mathrm{H}_2) $$for cutting metals. How many grams of CO$$_2$$ are produced when 54.6 g of C$$_2H$_2 is $$burned in excess oxygen? ($$2\mathrm{C}_2\mathrm{H}_2 + 5\mathrm{O}_2 \rightarrow 4\mathrm{CO}_2 + 2\mathrm{H}_2\mathrm{O})$$

Accepted Answer

$$185\ \mathrm{g}$$

Question 6

Given the reaction $$2\mathrm{K}(s) + \mathrm{Cl}_2(g) \rightarrow 2\mathrm{KCl}(s)$$, how many grams of K are required to produce 36.0 g of KCl?

Accepted Answer

$$18.9\ \mathrm{g}$$

Question 7

Which of the following best describes the steps needed to convert grams of substance A to grams of substance B in a chemical reaction?

Accepted Answer

Grams A $$\rightarrow$$ Moles A $$\rightarrow$$ Moles B $$\rightarrow$$ Grams B

Question 8

Heptane ($$\mathrm{C}_7\mathrm{H}_{16}) is an $$undesirable gasoline component. How many grams of O$$_2$$ are required to react with 22.5 g of C$$_7H$_{16}$$? ($$\mathrm{C}_7\mathrm{H}_{16} + 11\mathrm{O}_2 \rightarrow 7\mathrm{CO}_2 + 8\mathrm{H}_2\mathrm{O})$$

Accepted Answer

$$79.1\ \mathrm{g}$$

Question 9

Which of the following is NOT a piece of information you can obtain from a balanced chemical equation?

Accepted Answer

The speed at which the reaction occurs

Question 10

If 1.42 mol of Fe reacts with excess S in the reaction $$2\mathrm{Fe}(s) + 3\mathrm{S}(s) \rightarrow \mathrm{Fe}_2\mathrm{S}_3(s)$$, how many moles of S are required?

Accepted Answer

$$2.13\ \mathrm{mol}$$

Question 11

Which of the following is the correct mole–mole factor to convert from moles of C$$_3H$_8 to $$moles of CO$$_2 in $$the reaction $$\mathrm{C}_3\mathrm{H}_8 + 5\mathrm{O}_2 \rightarrow 3\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O}$$?

Accepted Answer

$$\frac{3\ \mathrm{mol}\ \mathrm{CO}_2}{1\ \mathrm{mol}\ \mathrm{C}_3\mathrm{H}_8}$$

Question 12

A propane torch is used in plumbing. If 2.25 mol of C$$_3H$_8 is $$burned, how many moles of H$$_2O $$are produced? ($$\mathrm{C}_3\mathrm{H}_8 + 5\mathrm{O}_2 \rightarrow 3\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O})$$

Accepted Answer

$$9.00\ \mathrm{mol}$$

Question 13

Which of the following is the correct sequence for a mass-to-mass calculation in a chemical reaction?

Accepted Answer

Grams A $$\rightarrow$$ Moles A $$\rightarrow$$ Moles B $$\rightarrow$$ Grams B

Question 14

Which of the following is a real-world application of the Law of Conservation of Mass?

Accepted Answer

The mass of a silver spoon before and after tarnishing remains the same if all products are collected.

Question 15

Which of the following is the correct molar mass for KCl?

Accepted Answer

$$74.55\ \mathrm{g/mol}$$

Question 16

If you have 100.2 g of C$$_7H$_{16}$$, how many moles do you have? (Molar mass of C$$_7H$_{16} = 100.2 g/$$mol)

Accepted Answer

$$1.00\ \mathrm{mol}$$

Question 17

Which of the following is the correct mole–mole factor to convert from moles of O$$_2 to $$moles of C$$_7H$_{16} in $$the reaction $$\mathrm{C}_7\mathrm{H}_{16} + 11\mathrm{O}_2 \rightarrow 7\mathrm{CO}_2 + 8\mathrm{H}_2\mathrm{O}$$?

Accepted Answer

$$\frac{1\ \mathrm{mol}\ \mathrm{C}_7\mathrm{H}_{16}}{11\ \mathrm{mol}\ \mathrm{O}_2}$$

Chemical Quantities in Reactions: Law of Conservation of Mass, Mole Relationships, and Mass Calculations

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