Q: What is Avogadro’s number, and what does it represent?

$$6.022 \times 10$$^{23}$$; the number of molecules or formula units in one mole of a substance.

Q: A cold medicine tablet contains 30.0 mg of pseudoephedrine hydrochloride (molar mass = 201.70 g/mol). How many molecules of pseudoephedrine hydrochloride are in the tablet?

$$8.95 \times 10$$^{19}$$ molecules

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

$$\text{Percent yield} = \frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100$$

Question 1

Which of the following statements best describes the mole in chemistry?

Accepted Answer

A mole is the amount of a substance whose mass in grams is numerically equal to its molecular or formula weight.

Question 2

What is Avogadro’s number, and what does it represent?

Accepted Answer

$$6.022 	imes 10$$^{23}$$; the number of molecules or formula units in one mole of a substance.

Question 3

A cold medicine tablet contains 30.0 mg of pseudoephedrine hydrochloride (molar mass = 201.70 g/mol). How many molecules of pseudoephedrine hydrochloride are in the tablet?

Accepted Answer

$$8.95 	imes 10$$^{19}$$ molecules

Question 4

Which of the following is the correct sequence of steps for solving a mass-to-mass stoichiometry problem?

Accepted Answer

Convert mass of reactant to moles, use mole ratio to find moles of product, convert moles of product to mass.

Question 5

Ibuprofen has a molecular weight of 206.3 g/mol. If a bottle contains 0.082 mol of ibuprofen, what is the mass of ibuprofen in the bottle?

Accepted Answer

$$16.9 g$$

Question 6

A reaction produces 0.022 g of calcium oxalate ($$\mathrm{CaC_2O_4}$$, molar mass = 128.1 g/mol). What mass of calcium chloride ($$\mathrm{$$CaCl_2$$}$$, molar mass = 111.0 g/mol) was used, assuming a 1:1 mole ratio?

Accepted Answer

$$0.019 g$$

Question 7

In the reaction $$2\mathrm{Fe} + \mathrm{O_2$} \rightarrow 2\mathrm{FeO}$$, how many moles of $$\mathrm{FeO}$$ are produced from 6.2 mol of iron?

Accepted Answer

6.2 mol

Question 8

A sample contains $$1.00 	imes 10$$^{18}$$ atoms of carbon. What is the mass of this sample in grams? (Atomic weight of C = 12.01 g/mol)

Accepted Answer

$$2.00 	imes 10$$^{-6}$$ g

Question 9

Which of the following best defines the limiting reagent in a chemical reaction?

Accepted Answer

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

Question 10

If the theoretical yield of $$\mathrm{CO_2$}$$ from the combustion of acetylene is 88.0 g, but only 72.4 g is actually obtained, what is the percent yield?

Accepted Answer

$$82.3\%$$

Question 11

A reaction has a percent yield of 78.5%. If the theoretical yield of ethyl alcohol is 41.1 g, how much ethyl alcohol is actually produced?

Accepted Answer

$$32.3 g$$

Question 12

Which of the following is NOT a correct use of a conversion factor in stoichiometry?

Accepted Answer

Using the molar mass to convert directly from grams of one substance to grams of another.

Question 13

In a reaction, 3.8 g of sodium hydrogen phosphate ($$\mathrm{Na_2HPO_4}$$, molar mass = 142.0 g/mol) is used. How many moles of $$\mathrm{Na_2HPO_4}$$ are present?

Accepted Answer

$$0.0268$$ mol

Question 14

Which of the following best describes the relationship between the coefficients in a balanced chemical equation and the mole ratios?

Accepted Answer

Coefficients indicate the mole ratios of reactants and products, which can be used as conversion factors in calculations.

Question 15

A reaction between boric oxide ($$\mathrm{B_2O_3}$$, molar mass = 69.6 g/mol) and magnesium ($$\mathrm{Mg}$$, molar mass = 24.3 g/mol) is used to produce boron. If 2350 g of $$\mathrm{B_2O_3}$$ and 3580 g of $$\mathrm{Mg}$$ are reacted, which is the limiting reagent?

Accepted Answer

$$\mathrm{B_2O_3}$$

Question 16

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

Accepted Answer

$$	ext{Percent yield} = \frac{	ext{Actual yield}}{	ext{Theoretical yield}} 	imes 100$$

Question 17

In the reaction $$2\mathrm{NO_2$} + \mathrm{H_2O} \rightarrow 2\mathrm{$$HNO_3$$} + \mathrm{NO}$$, how many grams of $$\mathrm{$$HNO_3$$} ($$molar mass = 63.0 g/mol) are produced from 1.0 mol of $$\mathrm{NO_2$}$$?

Accepted Answer

$$31.5 g$$

Question 18

Which of the following statements about molar mass is correct?

Accepted Answer

Molar mass is the mass in grams of one mole of a substance, numerically equal to its molecular weight.

Chemical Reactions: Mole and Mass Relationships (Chapter 6 Study Notes)

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