Q: A chemist wants to produce 100.0 g of water by reacting hydrogen gas with oxygen gas. The balanced equation is $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(g). $$What mass of hydrogen gas is required to produce 100.0 g of water, assuming excess oxygen?

$$100.0\,\text{g} \times \frac{1\,\text{mol}\,H_2O}{18.02\,\text{g}} \times \frac{2\,\text{mol}\,H_2$}{2\,\text{mol}\,H_2O} \times 2.02\,\text{g}\,H_2$ = 11.2\,\text{g}$$

Q: In the reaction $$2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$$, how many grams of $$O_2$$ are produced from 24.5 g of $$KClO_3$$?

$$24.5\,\text{g}\,$$KClO_3$$ \times \frac{1\,\text{mol}\,$$KClO_3$$}{122.55\,\text{g}} \times \frac{3\,\text{mol}\,O_2$}{2\,\text{mol}\,$$KClO_3$$} \times 32.00\,\text{g}\,O_2$ = 9.6\,\text{g}$$

Q: A plant consumes 37.8 g of $$CO_2 in $$one week. Using the balanced photosynthesis equation $$6CO_2(g) + 6H_2O(g) \rightarrow C_6H_{12}O_6$(aq) + 6O_2(g)$$, what mass of glucose ($$C_6H_{12}O_6$) can be synthesized?

$$37.8\,\text{g}\,CO_2$ \times \frac{1\,\text{mol}\,CO_2$}{44.011\,\text{g}} \times \frac{1\,\text{mol}\,C_6H_{12}O_6$}{6\,\text{mol}\,CO_2$} \times 180.2\,\text{g}\,C_6H_{12}O_6$ = 25.8\,\text{g}$$

Q: In the combustion of octane, $$2C_8H_{18}(l) + 25O_2(g) \rightarrow 16CO_2(g) + 18H_2O(g)$$, how many grams of $$CO_2$$ are produced from 11.0 moles of $$C_8H_{18}$$?

$$11.0\,\text{mol}\,C_8H_{18} \times \frac{16\,\text{mol}\,CO_2$}{2\,\text{mol}\,C_8H_{18}} \times 44.011\,\text{g}\,CO_2$ = 3.87 \times 10^3$\,\text{g}$$

Q: For the reaction $$2NO(g) + 5H_2(g) \rightarrow 2NH_3(g) + 2H_2O(g)$$, what is the theoretical yield of $$NH_3 (in $$grams) from 86.3 g $$NO$$ and 25.6 g $$H_2$$?

$$2.8757\,\text{mol}\,NO \times \frac{2\,\text{mol}\,NH_3$}{2\,\text{mol}\,NO} \times 17.03\,\text{g}\,NH_3$ = 49.0\,\text{g}$$

Q: In the synthesis of ammonia $$3H_2(g) + N_2$(g) \rightarrow 2NH_3(g)$$, what is the theoretical yield of $$NH_3 (in kg) $$from 5.22 kg $$H_2$$ and 31.5 kg $$N_2$$?

$$5.22\,\text{kg}\,H_2$ \times \frac{1000\,\text{g}}{1\,\text{kg}} \times \frac{1\,\text{mol}\,H_2$}{2.02\,\text{g}} = 2584\,\text{mol}\,H_2$; 31.5$$\,\text{kg}\,$$N_2$$ \times \frac{1000\,\text{g}}{1\,\text{kg}} \times \frac{1\,\text{mol}\,$$N_2$$}{28.02\,\text{g}} = 1125\,\text{mol}\,$$N_2$$; $$H_2 is $$limiting: $$2584\,\text{mol}\,H_2$ \times \frac{2\,\text{mol}\,NH_3$}{3\,\text{mol}\,H_2$} = 1723\,\text{mol}\,NH_3$; 1723$$\,\text{mol}\,$$NH_3$$ \times 17.03\,\text{g} = 29347\,\text{g} = 29.3\,\text{kg}$$

Q: A reaction produces 72.3 g of iron from 167 g $$Fe_2O_3$$ and 85.8 g $$CO$$ according to $$Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g). $$What is the percent yield of iron?

$$\%\,\text{yield} = \frac{72.3\,\text{g}}{114\,\text{g}} \times 100 = 63.5\%$$

Question 1

A chemist wants to produce 100.0 g of water by reacting hydrogen gas with oxygen gas. The balanced equation is $$2H_2(g) + O_2$(g) \rightarrow 2H_2O(g). $$What mass of hydrogen gas is required to produce 100.0 g of water, assuming excess oxygen?

Accepted Answer

$$100.0\,	ext{g} 	imes \frac{1\,	ext{mol}\,H_2O}{18.02\,	ext{g}} 	imes \frac{2\,	ext{mol}\,H_2$}{2\,	ext{mol}\,H_2O} 	imes 2.02\,	ext{g}\,H_2$ = 11.2\,	ext{g}$$

Question 2

In the reaction $$2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$$, how many grams of $$O_2$$ are produced from 24.5 g of $$KClO_3$$?

Accepted Answer

$$24.5\,	ext{g}\,$$KClO_3$$ 	imes \frac{1\,	ext{mol}\,$$KClO_3$$}{122.55\,	ext{g}} 	imes \frac{3\,	ext{mol}\,O_2$}{2\,	ext{mol}\,$$KClO_3$$} 	imes 32.00\,	ext{g}\,O_2$ = 9.6\,	ext{g}$$

Question 3

A plant consumes 37.8 g of $$CO_2 in $$one week. Using the balanced photosynthesis equation $$6CO_2(g) + 6H_2O(g) \rightarrow C_6H_{12}O_6$(aq) + 6O_2(g)$$, what mass of glucose ($$C_6H_{12}O_6$) can be synthesized?

Accepted Answer

$$37.8\,	ext{g}\,CO_2$ 	imes \frac{1\,	ext{mol}\,CO_2$}{44.011\,	ext{g}} 	imes \frac{1\,	ext{mol}\,C_6H_{12}O_6$}{6\,	ext{mol}\,CO_2$} 	imes 180.2\,	ext{g}\,C_6H_{12}O_6$ = 25.8\,	ext{g}$$

Question 4

In the combustion of octane, $$2C_8H_{18}(l) + 25O_2(g) \rightarrow 16CO_2(g) + 18H_2O(g)$$, how many grams of $$CO_2$$ are produced from 11.0 moles of $$C_8H_{18}$$?

Accepted Answer

$$11.0\,	ext{mol}\,C_8H_{18} 	imes \frac{16\,	ext{mol}\,CO_2$}{2\,	ext{mol}\,C_8H_{18}} 	imes 44.011\,	ext{g}\,CO_2$ = 3.87 	imes 10^3$\,	ext{g}$$

Question 5

Given the reaction $$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$, if you start with 5 molecules of CH_4$ and 8 molecules of O_2$, what is the limiting reagent and how many CO_2$ molecules can be produced?

Accepted Answer

Oxygen is the limiting reagent; 4 $$CO_2$$ molecules can be produced.

Question 6

In the reaction $$2NO(g) + 5H_2(g) \rightarrow 2NH_3(g) + 2H_2O(g)$$, starting with 86.3 g $$NO$$ and 25.6 g $$H_2$$, what is the limiting reagent?

Accepted Answer

$$NO is $$the limiting reagent.

Question 7

For the reaction $$2NO(g) + 5H_2(g) \rightarrow 2NH_3(g) + 2H_2O(g)$$, what is the theoretical yield of $$NH_3 (in $$grams) from 86.3 g $$NO$$ and 25.6 g $$H_2$$?

Accepted Answer

$$2.8757\,	ext{mol}\,NO 	imes \frac{2\,	ext{mol}\,NH_3$}{2\,	ext{mol}\,NO} 	imes 17.03\,	ext{g}\,NH_3$ = 49.0\,	ext{g}$$

Question 8

In the synthesis of ammonia $$3H_2(g) + N_2$(g) \rightarrow 2NH_3(g)$$, what is the theoretical yield of $$NH_3 (in kg) $$from 5.22 kg $$H_2$$ and 31.5 kg $$N_2$$?

Accepted Answer

$$5.22\,	ext{kg}\,H_2$ 	imes \frac{1000\,	ext{g}}{1\,	ext{kg}} 	imes \frac{1\,	ext{mol}\,H_2$}{2.02\,	ext{g}} = 2584\,	ext{mol}\,H_2$; 31.5$$\,	ext{kg}\,$$N_2$$ 	imes \frac{1000\,	ext{g}}{1\,	ext{kg}} 	imes \frac{1\,	ext{mol}\,$$N_2$$}{28.02\,	ext{g}} = 1125\,	ext{mol}\,$$N_2$$; $$H_2 is $$limiting: $$2584\,	ext{mol}\,H_2$ 	imes \frac{2\,	ext{mol}\,NH_3$}{3\,	ext{mol}\,H_2$} = 1723\,	ext{mol}\,NH_3$; 1723$$\,	ext{mol}\,$$NH_3$$ 	imes 17.03\,	ext{g} = 29347\,	ext{g} = 29.3\,	ext{kg}$$

Question 9

A reaction produces 72.3 g of iron from 167 g $$Fe_2O_3$$ and 85.8 g $$CO$$ according to $$Fe_2O_3(s) + 3CO(g) \rightarrow 2Fe(s) + 3CO_2(g). $$What is the percent yield of iron?

Accepted Answer

$$\%\,	ext{yield} = \frac{72.3\,	ext{g}}{114\,	ext{g}} 	imes 100 = 63.5\%$$

Question 10

Which of the following is NOT a reason why the actual yield of a reaction is less than the theoretical yield?

Accepted Answer

All reactants are completely converted to products.

Question 11

A solution is prepared by dissolving 390 mg of sodium ion in 200.0 g of solution. What is the concentration in ppm?

Accepted Answer

$$\frac{390\,	ext{mg}}{200.0\,	ext{g}} 	imes 10^6$ = 1.95 	imes 10^3$\,	ext{ppm}$$

Question 12

What is the molarity of a solution containing 0.50 mol of solute in 250 mL of solution?

Accepted Answer

$$M = \frac{0.50\,	ext{mol}}{0.250\,	ext{L}} = 2.0\,	ext{M}$$

Question 13

A 52.10 mL sample of 0.178 M HCl is diluted to 70.26 mL. What is the final molarity?

Accepted Answer

$$M_2$$ = \frac{M_1V_1}{$$V_2$$} = \frac{0.178 	imes 52.10}{70.26} = 0.132\,	ext{M}$$

Question 14

Which formula correctly expresses mass percentage in a solution?

Accepted Answer

$$	ext{Mass percentage} = \frac{	ext{mass of one component}}{	ext{mass of whole solution}} 	imes 100$$

Question 15

A chemist needs to prepare 500 mL of 0.250 M NaCl solution. How many grams of NaCl are required? ($$M_{NaCl} = 58.44\,	ext{g/mol})$$

Accepted Answer

$$0.250\,	ext{mol/L} 	imes 0.500\,	ext{L} 	imes 58.44\,	ext{g/mol} = 7.31\,	ext{g}$$

Question 16

Which equation is used to calculate the concentration in parts per billion (ppb)?

Accepted Answer

$$	ext{ppb} = \frac{	ext{mass of solute}}{	ext{mass of solution}} 	imes 10^9$

Question 17

A solution contains 10.0 g of ethanol in 90.0 g of water. What is the mass percentage of ethanol?

Accepted Answer

$$\frac{10.0\,	ext{g}}{10.0\,	ext{g} + 90.0\,	ext{g}} 	imes 100 = 10.0\%$$

Question 18

Which of the following statements about stoichiometry is TRUE?

Accepted Answer

Stoichiometry uses mole ratios from balanced equations to relate reactants and products.

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