Q: A student reacts 9.62 mL of benzene (C$$_6H$_6$$, density = 3.12 g/mL) with 65.0 g of Br$$_2 to $$make bromobenzene (C$$_6H$_5Br). If 56.7 g of $$bromobenzene is obtained, what is the percent yield? (Molar masses: C$$_6H$_6 = 78.11 g/$$mol, Br$$_2 = 159.8 g/$$mol, C$$_6H$_5Br = 157.01 g/$$mol)

$$ \frac{56.7}{63.1} \times 100\% = 89.9\%$$

Q: If the actual yield of water in the previous sucrose combustion reaction is 4.32 g, what is the percent yield?

$$ \frac{4.32}{3.22} \times 100\% = 134\%$$

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

$$ \frac{\text{Actual yield of product}}{\text{Theoretical yield of product}} \times 100\%$$

Question 1

Which law is demonstrated by the need to balance chemical equations, such as the combustion of methane shown in the image (CH$$_4 + 2O$_2$$ → CO$$_2 + 2H$_2O$$)?

Accepted Answer

Law of Conservation of Mass

Question 2

In the reaction CH$$_4 + 2O$_2$$ → CO$$_2 + 2H$_2O$$, what is the total number of oxygen atoms on the product side?

Accepted Answer

4

Question 3

Why is it incorrect to change subscripts when balancing a chemical equation?

Accepted Answer

Changing subscripts changes the identity of the substances involved.

Question 4

Given the unbalanced equation: C$$_4H$_{10} + O$_2$$ → CO$$_2 + H$_2O$$, what is the correct coefficient for O$$_2$$ after balancing?

Accepted Answer

$$
13/2
$$

Question 5

A recipe for cookies is given as: 1 cup butter + 3/4 cup sugar + 2 eggs + 1 tsp soda + 1 tsp H$$_2O + 2 1/4 $$cup flour + 1 tsp NaCl + chocolate chips + 1 tsp vanilla → 2 dozen cookies. If you only have 1 cup of butter, 2 eggs, and 1 tsp soda, but only 1/2 cup sugar, what is the limiting reactant?

Accepted Answer

Sugar

Question 6

In a reaction, 0.588 mol N$$_2$$ and 0.632 mol H$$_2$$ are mixed according to the equation: N$$_2 + 3H$_2$$ → 2NH$$_3. $$What is the limiting reactant?

Accepted Answer

H$$_2$$

Question 7

A student reacts 9.62 mL of benzene (C$$_6H$_6$$, density = 3.12 g/mL) with 65.0 g of Br$$_2 to $$make bromobenzene (C$$_6H$_5Br). If 56.7 g of $$bromobenzene is obtained, what is the percent yield? (Molar masses: C$$_6H$_6 = 78.11 g/$$mol, Br$$_2 = 159.8 g/$$mol, C$$_6H$_5Br = 157.01 g/$$mol)

Accepted Answer

$$
\frac{56.7}{63.1} 	imes 100\% = 89.9\%$$

Question 8

Which of the following best describes the term 'stoichiometry'?

Accepted Answer

The numerical relationship between quantities in a chemical reaction

Question 9

In the combustion of sucrose: C$$_{12}H$_{22}O$_{11} + 12 O$_2$$ → 12 CO$$_2 + 11 H$_2O$$, if 10.0 g of sucrose (molar mass = 342.3 g/mol) and 10.0 g of O$$_2 ($$molar mass = 32.00 g/mol) are reacted, what is the theoretical yield of water in grams?

Accepted Answer

3.22 g

Question 10

If the actual yield of water in the previous sucrose combustion reaction is 4.32 g, what is the percent yield?

Accepted Answer

$$
\frac{4.32}{3.22} 	imes 100\% = 134\%$$

Question 11

Which of the following is NOT a correct step in balancing a chemical equation?

Accepted Answer

Change the subscripts to balance the equation.

Question 12

In a reaction, the reactant that is completely consumed and determines the amount of product formed is called:

Accepted Answer

Limiting reactant

Question 13

If you have 4 buns, 6 cheese slices, and 5 meat patties, how many burgers can you make if each burger requires 1 of each ingredient?

Accepted Answer

4

Question 14

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

Accepted Answer

$$
\frac{	ext{Actual yield of product}}{	ext{Theoretical yield of product}} 	imes 100\%$$

Question 15

A reaction has two reactants, A and B. If you are given the amounts of both, what must you do before calculating the amount of product formed?

Accepted Answer

Identify the limiting reactant

Chemical Quantities and Aqueous Reactions: Stoichiometry, Limiting Reactants, and Yield

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