Q: Which formula is used to calculate percent yield in a chemical reaction?

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

Q: A scientist isolates 22.1 g of Cu from a reaction of 45.5 g Zn with 70.1 g CuSO$$_4. $$What is the percent yield if the theoretical yield of Cu is 31.8 g?

$$\frac{22.1}{31.8} \times 100\% = 69.5\%$$

Q: In the reaction $$2\text{C}_4\text{H}_{10} + 15\text{O}_2 \rightarrow 12\text{CO}_2 + 6\text{H}_2\text{O}$$, how many moles of water are produced from 2.6 g of C$$_4H$_{10}$$? (Molar mass of C$$_4H$_{10} = 58 g/$$mol)

$$\frac{2.6}{58} \times \frac{6}{2} = 0.135$$ mol

Q: If a reaction has a percent yield of 80%, and the theoretical yield is 50 g, what is the actual yield?

$$\frac{80}{100} \times 50 = 40 g$$

Q: Ammonia reacts with hypochlorite to produce hydrazine: $$2\text{NH}_3 + \text{OCl}^- \rightarrow \text{N}_2\text{H}_4 + \text{Cl}^- + \text{H}_2\text{O}. If 115.0 g NH$_3 is $$used and the percent yield is 81.5%, how many grams of hydrazine (N$$_2H$_4$$, molar mass = 32 g/mol) are produced?

$$\frac{115.0}{17} \times \frac{1}{2} \times 32 \times 0.815 = 88.48 g$$

Q: In the reduction of iron(III) oxide: $$\text{Fe}_2\text{O}_3 + 3\text{H}_2 \rightarrow 2\text{Fe} + 3\text{H}_2\text{O}$$, how many moles of Fe$$_2O$_3$$ are required to produce 0.850 moles of Fe if the reaction is only 75% complete?

$$\frac{0.850}{2 \times 0.75} = 0.567$$ mol

Q: A reaction produced 12.5 g of product, but the theoretical yield was 20.0 g. What is the percent yield?

$$\frac{12.5}{20.0} \times 100\% = 62.5\%$$

Question 1

Which formula is used to calculate percent yield in a chemical reaction?

Accepted Answer

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

Question 2

A scientist isolates 22.1 g of Cu from a reaction of 45.5 g Zn with 70.1 g CuSO$$_4. $$What is the percent yield if the theoretical yield of Cu is 31.8 g?

Accepted Answer

$$\frac{22.1}{31.8} 	imes 100\% = 69.5\%$$

Question 3

In the reaction $$2	ext{C}_4	ext{H}_{10} + 15	ext{O}_2 ightarrow 12	ext{CO}_2 + 6	ext{H}_2	ext{O}$$, how many moles of water are produced from 2.6 g of C$$_4H$_{10}$$? (Molar mass of C$$_4H$_{10} = 58 g/$$mol)

Accepted Answer

$$\frac{2.6}{58} 	imes \frac{6}{2} = 0.135$$ mol

Question 4

If a reaction has a percent yield of 80%, and the theoretical yield is 50 g, what is the actual yield?

Accepted Answer

$$\frac{80}{100} 	imes 50 = 40 g$$

Question 5

Ammonia reacts with hypochlorite to produce hydrazine: $$2	ext{NH}_3 + 	ext{OCl}^- ightarrow 	ext{N}_2	ext{H}_4 + 	ext{Cl}^- + 	ext{H}_2	ext{O}. If 115.0 g NH$_3 is $$used and the percent yield is 81.5%, how many grams of hydrazine (N$$_2H$_4$$, molar mass = 32 g/mol) are produced?

Accepted Answer

$$\frac{115.0}{17} 	imes \frac{1}{2} 	imes 32 	imes 0.815 = 88.48 g$$

Question 6

Which of the following best describes the relationship between actual yield and theoretical yield?

Accepted Answer

Actual yield is always less than theoretical yield due to inefficiencies.

Question 7

In the reduction of iron(III) oxide: $$	ext{Fe}_2	ext{O}_3 + 3	ext{H}_2 ightarrow 2	ext{Fe} + 3	ext{H}_2	ext{O}$$, how many moles of Fe$$_2O$_3$$ are required to produce 0.850 moles of Fe if the reaction is only 75% complete?

Accepted Answer

$$\frac{0.850}{2 	imes 0.75} = 0.567$$ mol

Question 8

A reaction produced 12.5 g of product, but the theoretical yield was 20.0 g. What is the percent yield?

Accepted Answer

$$\frac{12.5}{20.0} 	imes 100\% = 62.5\%$$

Question 9

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

Accepted Answer

All reactants are perfectly pure.

Question 10

If a reaction has a percent yield of 90% and the actual yield is 18 g, what is the theoretical yield?

Accepted Answer

$$\frac{18}{0.9} = 20 g$$

Question 11

A student calculates a percent yield of 105% for a reaction. What is the most likely explanation?

Accepted Answer

The product was contaminated or not completely dried.

Question 12

Which of the following percent yields would be considered 'Excellent' according to the study materials?

Accepted Answer

$$\u003e90\%$$

Question 13

In a chemical reaction, 5.0 g of reactant is used and 3.5 g of product is obtained. If the theoretical yield is 4.0 g, what is the percent yield?

Accepted Answer

$$\frac{3.5}{4.0} 	imes 100\% = 87.5\%$$

Question 14

Which step is necessary to convert grams of a reactant to grams of a product in a chemical reaction?

Accepted Answer

Convert grams to moles, use mole-to-mole ratio, then convert moles to grams.

Question 15

A reaction produces 10.0 g of product, but only 7.0 g is recovered. What is the percent yield?

Accepted Answer

$$\frac{7.0}{10.0} 	imes 100\% = 70\%$$

Question 16

If a reaction is 100% efficient, what is the relationship between actual yield and theoretical yield?

Accepted Answer

Actual yield equals theoretical yield.

Question 17

Which of the following is a real-world reason for a low percent yield in a pharmaceutical synthesis?

Accepted Answer

Loss of product during purification steps.

Question 18

A reaction has a theoretical yield of 25.0 g and an actual yield of 20.0 g. What is the percent yield?

Accepted Answer

$$\frac{20.0}{25.0} 	imes 100\% = 80\%$$

Percent Yield and Stoichiometry in Chemical Reactions

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