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?

$$\frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100$$

Question 1

Which of the following statements best describes Avogadro’s number?

Accepted Answer

It is the number of molecules in 1 mole of a substance, approximately $$6.02 	imes 10$$^{23}$$.

Question 2

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 3

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

Accepted Answer

Write the balanced equation, convert mass to moles, use mole ratio, convert moles to mass.

Question 4

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 5

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

Accepted Answer

$$1.99 	imes 10$$^{-6}$$ g

Question 6

In the reaction $$4Fe + 3O_2 \rightarrow 2Fe_2O_3$$, what is the mole ratio of $$Fe to$$ $$Fe_2O_3$$?

Accepted Answer

$$4:2$$

Question 7

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

Accepted Answer

$$0.019 g$$

Question 8

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 9

If the theoretical yield of $$CO_2$$ 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 10

A reaction of $$2350 g of $$boric oxide ($$B_2O_3$$, molar mass $$69.6 g/$$mol) with $$3580 g of $$magnesium ($$Mg$$, molar mass $$24.3 g/$$mol) produces boron. If the balanced equation is $$B_2O_3 + 3Mg \rightarrow 2B + 3MgO$$, what is the theoretical yield of boron in grams?

Accepted Answer

$$729 g$$

Question 11

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

Accepted Answer

$$\frac{	ext{Actual Yield}}{	ext{Theoretical Yield}} 	imes 100$$

Question 12

Ethylene ($$C_2H_4) $$reacts with water to form ethyl alcohol ($$C_2H_5OH) $$with a $$78.5\%$$ actual yield. If $$25.0 g of $$ethylene (molar mass $$28.0 g/$$mol) is used, how many grams of ethyl alcohol (molar mass $$46.0 g/$$mol) are actually formed?

Accepted Answer

$$32.3 g$$

Question 13

Which of the following statements about molar mass is correct?

Accepted Answer

Molar mass is the mass in grams of 1 mole of a substance and is numerically equal to its molecular weight.

Question 14

A balanced chemical equation shows $$2H_2 + O_2$ \rightarrow 2H_2O. If $$you start with $$4$$ moles of $$H_2$$ and $$2$$ moles of $$O_2$$, what is the limiting reagent and how many moles of $$H_2O$$ can be formed?

Accepted Answer

Both are present in exact stoichiometric amounts; $$4$$ moles of $$H_2O$$ are formed.

Question 15

In a laboratory, $$1.0$$ mole of $$NO_2$$ reacts with water to produce nitric acid ($$HNO_3) $$with a molar mass of $$63.0 g/$$mol. How many grams of $$HNO_3$$ are produced per mole of $$NO_2$$ reacted, assuming a 1:1 mole ratio?

Accepted Answer

$$63.0 g$$

Question 16

A dose of sodium hydrogen phosphate ($$Na_2HPO_4) is$$ $$3.8 g. If $$the molar mass is $$142.0 g/$$mol, how many moles of $$Na^+$$ ions are in this dose? (Each formula unit contains 2 $$Na^+$$ ions.)

Accepted Answer

$$0.054$$ mol

Question 17

Which of the following is NOT a correct use of a mole ratio from a balanced chemical equation?

Accepted Answer

To convert between grams of different reactants or products directly.

Question 18

A student mixes $$5.0 g of$$ $$A ($$molar mass $$50.0 g/$$mol) and $$10.0 g of$$ $$B ($$molar mass $$100.0 g/$$mol) in a reaction with the equation $$A + 2B \rightarrow C. $$What is the limiting reagent?

Accepted Answer

$$B$$

Chapter 6: Chemical Reactions—Mole and Mass Relationships

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