Q: Which of the following is the correct formula for calculating molar mass?

$\text{Molar mass} = \dfrac{\text{mass (g)}}{\text{moles (mol)}}$

Question 1

Which of the following best describes a combustion reaction?

Accepted Answer

A reaction in which a substance reacts with oxygen to produce heat and light, typically forming $\mathrm{CO_2}$ and $\mathrm{H_2O}$.

Question 2

Given the reaction $2\mathrm{NH_3} + \dfrac{3}{2}\mathrm{I_2} \rightarrow 2\mathrm{NH_3I}$, how many grams of $\mathrm{I_2}$ are required to react completely with 5.2 g of $\mathrm{NH_3}$? (Molar masses: $\mathrm{NH_3} = 17.0\ \mathrm{g/mol}$, $\mathrm{I_2} = 254\ \mathrm{g/mol}$)

Accepted Answer

$11.6\ \mathrm{g}$

Question 3

A sample of a metal oxide $\mathrm{MO}$ is heated and its mass increases from $2.22\ \mathrm{g}$ to $3.70\ \mathrm{g}$ after complete oxidation. What is the percent by mass of oxygen in the final product?

Accepted Answer

$40.0\%$

Question 4

Which of the following is the correct balanced equation for the complete combustion of glucose ($\mathrm{C_6H_{12}O_6}$)?

Accepted Answer

$\mathrm{C_6H_{12}O_6} + 6\mathrm{O_2} \rightarrow 6\mathrm{CO_2} + 6\mathrm{H_2O}$

Question 5

If 2.5 g of $\mathrm{I_2}$ is used in the reaction $2\mathrm{NH_3} + \dfrac{3}{2}\mathrm{I_2} \rightarrow 2\mathrm{NH_3I}$, what is the theoretical yield of $\mathrm{NH_3I}$ in grams? (Molar masses: $\mathrm{NH_3I} = 143\ \mathrm{g/mol}$, $\mathrm{I_2} = 254\ \mathrm{g/mol}$)

Accepted Answer

$1.41\ \mathrm{g}$

Question 6

A student performs a reaction and obtains a 75% yield. If the theoretical yield is $10.0\ \mathrm{g}$, what is the actual yield?

Accepted Answer

$7.5\ \mathrm{g}$

Question 7

Which of the following statements about limiting reactants is correct?

Accepted Answer

The limiting reactant is the one that produces the least amount of product.

Question 8

In a decomposition reaction, $\mathrm{CaCO_3(s)} \rightarrow \mathrm{CaO(s)} + \mathrm{CO_2(g)}$, what mass of $\mathrm{CO_2}$ is produced from $50.0\ \mathrm{g}$ of $\mathrm{CaCO_3}$? (Molar masses: $\mathrm{CaCO_3} = 100\ \mathrm{g/mol}$, $\mathrm{CO_2} = 44\ \mathrm{g/mol}$)

Accepted Answer

$22.0\ \mathrm{g}$

Question 9

Which of the following is a characteristic of an incomplete combustion reaction?

Accepted Answer

It produces $\mathrm{CO}$ and/or soot in addition to $\mathrm{CO_2}$ and $\mathrm{H_2O}$.

Question 10

A 10.0 g sample of a compound containing only carbon, hydrogen, and oxygen is combusted, producing 14.7 g of $\mathrm{CO_2}$ and 6.0 g of $\mathrm{H_2O}$. What is the empirical formula of the compound?

Accepted Answer

$\mathrm{C_2H_6O}$

Question 11

Which of the following best explains why the maximum percent yield in a chemical reaction is rarely 100%?

Accepted Answer

Some product is always lost due to side reactions, incomplete reactions, or during purification.

Question 12

If 2.00 mol of $\mathrm{NH_3}$ reacts with 2.00 mol of $\mathrm{I_2}$ according to $2\mathrm{NH_3} + \dfrac{3}{2}\mathrm{I_2} \rightarrow 2\mathrm{NH_3I}$, which reactant is limiting?

Accepted Answer

$\mathrm{I_2}$

Question 13

A reaction has a theoretical yield of $5.0\ \mathrm{g}$, but after drying, only $4.0\ \mathrm{g}$ of product is recovered. What is the percent yield?

Accepted Answer

$80\%$

Question 14

Which of the following is the correct formula for calculating molar mass?

Accepted Answer

$	ext{Molar mass} = \dfrac{	ext{mass (g)}}{	ext{moles (mol)}}$

Question 15

In the reaction $\mathrm{C_2H_5OH} + 3\mathrm{O_2} \rightarrow 2\mathrm{CO_2} + 3\mathrm{H_2O}$, what mass of $\mathrm{CO_2}$ is produced from 46 g of $\mathrm{C_2H_5OH}$? (Molar masses: $\mathrm{C_2H_5OH} = 46\ \mathrm{g/mol}$, $\mathrm{CO_2} = 44\ \mathrm{g/mol}$)

Accepted Answer

$88\ \mathrm{g}$

Question 16

Which of the following is NOT a sign of a chemical reaction?

Accepted Answer

A change in state from solid to liquid due to heating.

Question 17

A 5.00 g sample of a hydrate loses 1.80 g of water upon heating. What is the percent by mass of water in the hydrate?

Accepted Answer

$36.0\%$

Question 18

Which of the following best describes a decomposition reaction?

Accepted Answer

A single compound breaks down into two or more simpler substances.

Question 19

In a combustion analysis, a 2.00 g sample of a hydrocarbon produces 6.60 g of $\mathrm{CO_2}$ and 2.70 g of $\mathrm{H_2O}$. What is the empirical formula of the hydrocarbon?

Accepted Answer

$\mathrm{C_3H_8}$

Stoichiometry, Chemical Reactions, and Composition Analysis

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