Q: How many molecules are present in 4.8 moles of $\mathrm{CO}_2$?

$2.89 \times 10^{24}$ molecules

Q: Which calculation would you perform to determine the mass percent of an element in a compound?

$\frac{\text{mass of element in 1 mole}}{\text{molar mass of compound}} \times 100$

Question 1

Which of the following best describes the relationship between the empirical formula and the molecular formula of a compound?

Accepted Answer

The molecular formula is a whole-number multiple of the empirical formula.

Question 2

A laboratory analysis gives the following mass percentages for a compound: 52.1% C, 6.6% H, and 41.3% O. What is the empirical formula of the compound? (Assume a 100 g sample.)

Accepted Answer

$\mathrm{C}_2\mathrm{H}_4\mathrm{O}$

Question 3

How many molecules are present in 4.8 moles of $\mathrm{CO}_2$?

Accepted Answer

$2.89 	imes 10^{24}$ molecules

Question 4

Given the balanced equation $\mathrm{C}_2\mathrm{H}_5\mathrm{OH} + 5\mathrm{O}_2 \rightarrow 3\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O} + 200\ \mathrm{kJ}$, how many moles of $\mathrm{O}_2$ are required to completely react with 2 moles of $\mathrm{C}_2\mathrm{H}_5\mathrm{OH}$?

Accepted Answer

10 moles

Question 5

If you have 45 grams of $\mathrm{C}_2\mathrm{H}_6\mathrm{O}_2$ (molar mass = 62 g/mol) and 152 grams of $\mathrm{O}_2$ (molar mass = 32 g/mol), which is the limiting reactant in the reaction $\mathrm{C}_2\mathrm{H}_6\mathrm{O}_2 + O_2 \rightarrow CO_2 + H_2O$?

Accepted Answer

$\mathrm{C}_2\mathrm{H}_6\mathrm{O}_2$

Question 6

How many oxygen atoms are in 25 molecules of $\mathrm{CO}_2$?

Accepted Answer

50

Question 7

What is the mass of 1.5 moles of $\mathrm{H}_2\mathrm{O}$? (Molar mass of $\mathrm{H}_2\mathrm{O}$ = 18 g/mol)

Accepted Answer

27 g

Question 8

A reaction yields 15.0 g of product, but the theoretical yield is 20.0 g. What is the percent yield?

Accepted Answer

$75\%$

Question 9

Which of the following is NOT a key conversion factor in compound stoichiometry?

Accepted Answer

Density (g/mL)

Question 10

How many moles of $\mathrm{CO}_2$ are produced when 3 moles of $\mathrm{C}_2\mathrm{H}_5\mathrm{OH}$ react completely according to the equation $\mathrm{C}_2\mathrm{H}_5\mathrm{OH} + 5\mathrm{O}_2 \rightarrow 3\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O}$?

Accepted Answer

9 moles

Question 11

If you have 5.45 grams of $\mathrm{O}_2$ (molar mass = 32 g/mol), how many oxygen atoms are present?

Accepted Answer

$2.05 	imes 10^{23}$ atoms

Question 12

Which step is necessary to convert from grams of a compound to number of molecules?

Accepted Answer

Divide by molar mass, then multiply by Avogadro's number

Question 13

A sample contains $3.01 	imes 10^{23}$ molecules of $\mathrm{CO}_2$. How many moles of $\mathrm{CO}_2$ is this?

Accepted Answer

0.5 moles

Question 14

Which of the following best explains why the limiting reactant determines the amount of product formed in a chemical reaction?

Accepted Answer

It is completely consumed first, stopping the reaction.

Question 15

Which calculation would you perform to determine the mass percent of an element in a compound?

Accepted Answer

$\frac{	ext{mass of element in 1 mole}}{	ext{molar mass of compound}} 	imes 100$

Compound Stoichiometry and Reaction Stoichiometry: Key Concepts and Practice

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