Q: Which of the following is the correct formula for calculating percent yield?

$$\frac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$$

Question 1

A power plant emits sulfur dioxide (SO$$_2) as a $$byproduct of burning coal. To reduce acid rain, the plant uses a scrubber that reacts SO$$_2$$ with calcium carbonate (CaCO$$_3) $$and water in the presence of oxygen to form calcium sulfate dihydrate (gypsum) and carbon dioxide. What is the balanced chemical equation for this process?

Accepted Answer

$$2\ \mathrm{SO}_2(g) + 2\ \mathrm{CaCO}_3(s) + 2\ \mathrm{H}_2\mathrm{O}(l) + \mathrm{O}_2(g) \rightarrow 2\ \mathrm{CaSO}_4\cdot2\mathrm{H}_2\mathrm{O}(s) + 2\ \mathrm{CO}_2(g)$$

Question 2

In the reaction $$2\ \mathrm{ZnS}(s) + 3\ \mathrm{O}_2(g) ightarrow 2\ \mathrm{ZnO}(s) + 2\ \mathrm{SO}_2(g)$$, how many kilograms of oxygen gas are required to react completely with $$5.00 	imes 10^3$ g of zinc sulfide (ZnS)? (Molar masses: ZnS = 97.46 g/mol, O_2$ = 32.00 g/mol)

Accepted Answer

$$2.46\ \mathrm{kg}$$

Question 3

A mixture of 15.0 g of carbon disulfide (CS$$_2) $$and 35.0 g of oxygen (O$$_2) $$reacts according to $$\mathrm{CS}_2(g) + 3\ \mathrm{O}_2(g) \rightarrow \mathrm{CO}_2(g) + 2\ \mathrm{SO}_2(g). $$What is the limiting reactant?

Accepted Answer

Carbon disulfide (CS$$_2)$$

Question 4

In the same reaction as above, how many grams of sulfur dioxide (SO$$_2) $$are produced?

Accepted Answer

$$25.2\ \mathrm{g}$$

Question 5

If 0.30 mol of Zn is added to hydrochloric acid containing 0.52 mol of HCl, according to $$\mathrm{Zn}(s) + 2\ \mathrm{HCl}(aq) \rightarrow \mathrm{ZnCl}_2(aq) + \mathrm{H}_2(g)$$, how many moles of H$$_2$$ are produced?

Accepted Answer

$$0.26\ \mathrm{mol}$$

Question 6

A student reacts 0.800 g of sodium hydrogen carbonate (NaHCO$$_3) $$with excess hydrochloric acid and obtains 0.420 g of sodium chloride (NaCl). What is the percent yield? (Molar mass NaHCO$$_3 = 84.01 g/$$mol, NaCl = 58.44 g/mol)

Accepted Answer

$$75.5\%$$

Question 7

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

Accepted Answer

The reactant that is completely consumed first, limiting the amount of product formed

Question 8

In a reaction, 1.50 g of salicylic acid (C$$_7H$_6O$_3) $$reacts with 11.20 g of methanol (CH$$_3OH) to $$produce 1.31 g of methyl salicylate (C$$_8H$_8O$_3). $$What is the percent yield? (Molar mass C$$_7H$_6O$_3 = 138.12 g/$$mol, C$$_8H$_8O$_3 = 152.15 g/$$mol)

Accepted Answer

$$79.2\%$$

Question 9

Which of the following is the correct formula for calculating percent yield?

Accepted Answer

$$\frac{	ext{actual yield}}{	ext{theoretical yield}} 	imes 100\%$$

Question 10

A chemical reaction has a theoretical yield of 10.0 g, but only 7.5 g of product is actually obtained. What is the percent yield?

Accepted Answer

$$75\%$$

Question 11

Which step is NOT part of the general guidelines for solving stoichiometry problems?

Accepted Answer

Assume all reactants are limiting

Question 12

If you have 10 cups of cheese, dough for 6 crusts, and 50 oz of sauce, and each pizza requires 2 cups of cheese, 1 crust, and 5 oz of sauce, what is the maximum number of pizzas you can make?

Accepted Answer

5

Question 13

In the reaction $$2\ \mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2\ \mathrm{H}_2\mathrm{O}$$, if you start with 10 molecules of H$$_2$$ and 7 molecules of O$$_2$$, how many molecules of O$$_2$$ remain after the reaction goes to completion?

Accepted Answer

2

Question 14

A reaction has an actual yield of 0.420 g and a theoretical yield of 0.556 g. What is the percent yield?

Accepted Answer

$$75.5\%$$

Question 15

Which of the following statements about theoretical yield is correct?

Accepted Answer

It is the maximum amount of product that can be formed from the limiting reactant

Question 16

A power plant needs to remove 1.00 metric ton (1000 kg) of SO$$_2$$ from its exhaust. How many kilograms of CaCO$$_3$$ are required? (Use the balanced equation: $$2\ \mathrm{SO}_2 + 2\ \mathrm{CaCO}_3 + 2\ \mathrm{H}_2\mathrm{O} + \mathrm{O}_2 \rightarrow 2\ \mathrm{CaSO}_4\cdot2\mathrm{H}_2\mathrm{O} + 2\ \mathrm{CO}_2$$; Molar masses: SO$$_2 = 64.07 g/$$mol, CaCO$$_3 = 100.09 g/$$mol)

Accepted Answer

$$1,563\ \mathrm{kg}$$

Question 17

Which of the following is NOT a correct use of the mole ratio in stoichiometric calculations?

Accepted Answer

To convert grams of a substance directly to grams of another without using moles

Question 18

A reaction mixture contains 0.50 mol of A and 0.80 mol of B. The balanced equation is $$A + 2B \rightarrow C. $$What is the limiting reactant?

Accepted Answer

B

Question 19

Which of the following best explains why actual yield is usually less than theoretical yield in a chemical reaction?

Accepted Answer

Some product is lost during purification or transfer

Stoichiometry, Limiting Reactants, and Reaction Yield in General Chemistry

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