Q: If 2.50 mol of caffeine ($$\mathrm{C_8H_{10}N_4O_2}) $$contains 15.0 mol of nitrogen atoms, how many nitrogen atoms are in 1.00 mol of caffeine?

6.02 \times $$10^{23}$$ \times 4

Q: If 97.0 g of caffeine ($$\mathrm{C_8H_{10}N_4O_2}) is $$equivalent to 0.499 mol, what is the molar mass of caffeine?

$$\frac{97.0\ \text{g}}{0.499\ \text{mol}}$$

Question 1

How many nitrogen atoms are present in 2.50 mol of caffeine ($$\mathrm{C_8H_{10}N_4O_2}$$)?

Accepted Answer

15.0 mol N atoms

Question 2

How many moles of caffeine ($$\mathrm{C_8H_{10}N_4O_2}) $$are present in 97.0 g of caffeine?

Accepted Answer

0.499 mol

Question 3

What mass of $$\mathrm{CO_2$} is $$produced when 30.0 g of caffeine ($$\mathrm{C_8H_{10}N_4O_2}) $$reacts completely with excess oxygen to form carbon dioxide and water?

Accepted Answer

112 g

Question 4

Aluminum reacts with oxygen to form aluminum oxide according to the equation: $$4\mathrm{Al} + 3\mathrm{O_2$} \rightarrow 2\mathrm{Al_2O_3}. If 27.0 g of Al $$reacts with excess oxygen, what is the percent yield if 40.8 g of $$\mathrm{Al_2O_3}$$ are actually produced?

Accepted Answer

80.0\%

Question 5

What mass of water ($$\mathrm{H_2O}) $$can be formed when 10.0 g of hydrogen reacts with 80.0 g of oxygen? $$2\mathrm{H_2$} + \mathrm{O_2$} \rightarrow 2\mathrm{H_2O}$$

Accepted Answer

72.1 g

Question 6

In the reaction $$4\mathrm{Al} + 3\mathrm{O_2$} \rightarrow 2\mathrm{Al_2O_3}$$, what is the limiting reagent when 27.0 g of Al reacts with 40.8 g of $$\mathrm{Al_2O_3}$$ produced?

Accepted Answer

Aluminum (Al)

Question 7

If 2.50 mol of caffeine ($$\mathrm{C_8H_{10}N_4O_2}) $$contains 15.0 mol of nitrogen atoms, how many nitrogen atoms are in 1.00 mol of caffeine?

Accepted Answer

6.02 	imes $$10^{23}$$ 	imes 4

Question 8

A student mixes 10.0 g of hydrogen and 80.0 g of oxygen. Which reactant is the limiting reagent in the formation of water ($$\mathrm{H_2O}$$)?

Accepted Answer

Oxygen ($$\mathrm{O_2$})$$

Question 9

What is the theoretical yield of $$\mathrm{Al_2O_3} (in $$grams) when 27.0 g of Al reacts with excess oxygen?

Accepted Answer

51.0 g

Question 10

If the percent yield of a reaction is calculated as $$\frac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100\%$$, what is the percent yield if the actual yield is 40.8 g and the theoretical yield is 51.0 g?

Accepted Answer

80.0\%

Question 11

Which of the following best describes the process for determining the mass of $$\mathrm{CO_2$}$$ produced from 30.0 g of caffeine ($$\mathrm{C_8H_{10}N_4O_2}) in a $$combustion reaction?

Accepted Answer

Convert mass to moles, use stoichiometry, convert moles to mass

Question 12

If 97.0 g of caffeine ($$\mathrm{C_8H_{10}N_4O_2}) is $$equivalent to 0.499 mol, what is the molar mass of caffeine?

Accepted Answer

$$\frac{97.0\ 	ext{g}}{0.499\ 	ext{mol}}$$

Question 13

In a reaction, if the limiting reagent is oxygen ($$\mathrm{O_2$}$$), what does this mean?

Accepted Answer

Oxygen will be completely consumed first, limiting the amount of product formed

Question 14

Which equation correctly represents the combustion of caffeine ($$\mathrm{C_8H_{10}N_4O_2}) to $$form carbon dioxide and water?

Accepted Answer

$$\mathrm{C_8H_{10}N_4O_2} + O_2$ \rightarrow CO_2$ + H_2O$$

Question 15

If 4.00 mol of water ($$\mathrm{H_2O}) $$can be produced from a reaction, what is the mass of water formed? (Molar mass of $$\mathrm{H_2O} = 18.0 g/$$mol)

Accepted Answer

72.0 g

Stoichiometry and Mole Calculations – Exam 5 Practice Guidance

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