Question 1

A balloon filled with nitrogen triiodide (NI3) is popped, causing a rapid decomposition reaction as shown in the first image sequence. Which of the following best describes the chemical principle demonstrated in this experiment?

Accepted Answer

The reaction demonstrates the rapid release of energy from a highly sensitive explosive due to the decomposition of NI3.

Question 2

Given the reaction: $$\mathrm{NH_3$(g) + 3 I_2$(s) \rightarrow NI_3$ \cdot NH_3$(s) + 3 HI(aq)}$$, how many grams of $$\mathrm{I_2$}$$ are required to produce 5.0 g of explosive product ($$\mathrm{NI_3$ \cdot NH_3$}$$, MW = 411.7 g/mol)? (MW of $$\mathrm{I_2$} = 253.8 g/$$mol)

Accepted Answer

$$\displaystyle 9.25\ \mathrm{g}$$

Question 3

A student combusts a hydrocarbon and collects 2.20 g of $$\mathrm{CO_2$}$$ and 0.90 g of $$\mathrm{H_2O}. $$What is the empirical formula of the hydrocarbon?

Accepted Answer

$$\mathrm{CH_3$}$$

Question 4

In a combustion train (see the diagram), what is the purpose of the $$\mathrm{$$MgSO_4$$}$$ absorber?

Accepted Answer

To absorb water vapor produced during combustion.

Question 5

A 22.2 g sample of an unknown metal is heated in air and forms 37.0 g of its oxide. If the oxide is $$\mathrm{MO_2$}$$, what is the molar mass of the metal, and which element is it most likely to be?

Accepted Answer

48.0 g/mol, likely titanium

Question 6

In the thermite reaction $$\mathrm{Fe_2O_3 + 2 Al \rightarrow 2 Fe + Al_2O_3}$$, if you start with 15.0 g of $$\mathrm{Fe_2O_3}$$ and 4.0 g of Al, what is the limiting reagent?

Accepted Answer

Aluminum

Question 7

Using the thermite reaction, how many grams of iron ($$\mathrm{Fe}$$, MW = 55.85 g/mol) can be produced from 4.0 g of Al (MW = 26.98 g/mol)?

Accepted Answer

$$\displaystyle 8.27\ \mathrm{g}$$

Question 8

A 27 m$$^3$$ room contains 7.5 kg of $$\mathrm{O_2$}$$ and a 4.0 kg iron anchor chain. Using the reaction $$4 \mathrm{Fe} + 3 \mathrm{O_2$} \rightarrow 2 \mathrm{Fe_2O_3}$$, what is the limiting reagent?

Accepted Answer

Iron

Question 9

After the iron in the previous question is completely oxidized, how much $$\mathrm{O_2$} (in kg) $$remains in the room?

Accepted Answer

$$\displaystyle 5.8\ \mathrm{kg}$$

Question 10

A sample containing C, H, and N is combusted, producing 0.311 g $$\mathrm{H_2O}$$ and 0.897 g $$\mathrm{CO_2$}. If $$the original sample mass is 0.5460 g, what is the empirical formula?

Accepted Answer

$$\mathrm{C_5H_5N}$$

Question 11

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

Accepted Answer

The reactant that is completely consumed, determining the maximum amount of product formed.

Question 12

In a combustion analysis, why is it important to use absorbers for $$\mathrm{H_2O}$$ and $$\mathrm{CO_2$}$$?

Accepted Answer

To accurately measure the amount of C and H in the sample by determining the mass of $$\mathrm{CO_2$}$$ and $$\mathrm{H_2O}$$ produced.

Question 13

If the theoretical yield of a reaction is 5.0 g and the actual yield is 4.8 g, what is the percent yield?

Accepted Answer

$$\displaystyle 96\%$$

Question 14

A hydrocarbon has the empirical formula $$\mathrm{C_5H_{12}}. $$What is the molecular formula if its molar mass is 86 g/mol?

Accepted Answer

$$\mathrm{C_5H_{12}}$$

Question 15

Which of the following is a real-world hazard associated with the oxidation of iron in confined spaces, as shown in the last image?

Accepted Answer

The depletion of oxygen, leading to asphyxiation.

Stoichiometry and Reaction Calculations in General Chemistry

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