Q: A cold medicine tablet contains 30.0 mg of pseudoephedrine hydrochloride ($$\mathrm{C$$_{10}$$H_{16}$$ClNO}$, MW = 201.70 g/mol). How many molecules of pseudoephedrine hydrochloride are in the tablet?

$$8.96 \times 10$$^{19}$$ molecules

Question 1

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

Accepted Answer

It is the number of molecules in 1 mole of any substance.

Question 2

Calculate the molar mass of sodium sulfate, $$\mathrm{Na_2SO_4}$$, using the following atomic weights: Na = 22.99, S = 32.07, O = 16.00.

Accepted Answer

$$\mathrm{142.05\ g/mol}$$

Question 3

A cold medicine tablet contains 30.0 mg of pseudoephedrine hydrochloride ($$\mathrm{C$$_{10}$$H_{16}$$ClNO}$, MW = 201.70 g/mol). How many molecules of pseudoephedrine hydrochloride are in the tablet?

Accepted Answer

$$8.96 	imes 10$$^{19}$$ molecules

Question 4

A pencil mark contains $$3 	imes 10$$^{17}$$ atoms of carbon. What is the mass of this pencil mark in grams? (Atomic weight of C = 12.01 g/mol)

Accepted Answer

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

Question 5

How many grams of ibuprofen ($$\mathrm{C$$_{13}$$H_{18}O_2$}$$, MW = 206.3 g/mol) are present in a bottle containing 0.082 mol of ibuprofen?

Accepted Answer

$$17\ \mathrm{g}$$

Question 6

A patient takes 3.8 g of sodium hydrogen phosphate ($$\mathrm{Na_2HPO_4}$$, MW = 142.0 g/mol) as a laxative. How many moles of $$\mathrm{Na^+}$$ ions are in this dose?

Accepted Answer

$$0.054\ \mathrm{mol}$$

Question 7

For the reaction $$4\ \mathrm{Fe} + 3\ \mathrm{O_2$} \rightarrow 2\ \mathrm{Fe_2O_3}$$, how many moles of $$\mathrm{Fe_2O_3}$$ are produced from 6.2 mol of Fe?

Accepted Answer

$$3.1\ \mathrm{mol}$$

Question 8

In the reaction $$3\ \mathrm{NO_2$} + \mathrm{H_2O} \rightarrow 2\ \mathrm{$$HNO_3$$} + \mathrm{NO}$$, how many grams of $$\mathrm{$$HNO_3$$} (MW = 63.0 g/$$mol) are produced from 1.0 mol of $$\mathrm{NO_2$}$$?

Accepted Answer

$$42\ \mathrm{g}$$

Question 9

A reaction produces 0.022 g of calcium oxalate ($$\mathrm{CaC_2O_4}$$, MW = 128.1 g/mol). What mass of calcium chloride ($$\mathrm{$$CaCl_2$$}$$, MW = 111.0 g/mol) was used as reactant?

Accepted Answer

$$0.019\ \mathrm{g}$$

Question 10

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

Accepted Answer

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

Question 11

The combustion of acetylene ($$\mathrm{C_2H_2}) $$produces 72.4 g of $$\mathrm{CO_2$}$$, but the theoretical yield is 88.0 g. What is the percent yield?

Accepted Answer

$$82.3\%$$

Question 12

A chemical plant reacts 2350 g of boric oxide ($$\mathrm{B_2O_3}$$, MW = 69.6 g/mol) with 3580 g of magnesium (MW = 24.3 g/mol) to produce boron. Which is the limiting reagent?

Accepted Answer

$$\mathrm{B_2O_3}$$

Question 13

If 25.0 g of ethylene ($$\mathrm{C_2H_4}$$, MW = 28.0 g/mol) reacts with excess water to form ethyl alcohol ($$\mathrm{C_2H_5OH}$$, MW = 46.0 g/mol) with a 78.5% yield, how many grams of ethyl alcohol are actually formed?

Accepted Answer

$$32.3\ \mathrm{g}$$

Question 14

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

Accepted Answer

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

Question 15

Which of the following best describes the relationship between mass, moles, and number of particles?

Accepted Answer

Mass must first be converted to moles, then moles to number of particles using Avogadro’s number.

Question 16

In a balanced chemical equation, what do the coefficients represent?

Accepted Answer

The number of moles or molecules of each substance.

Question 17

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

Accepted Answer

Using the number of atoms to directly convert to grams without using moles.

Chemical Reactions: Mole and Mass Relationships

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