Question 1

Which of the following is the correct empirical formula for a compound that is 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Accepted Answer

$$\mathrm{CH}_2\mathrm{O}$$

Question 2

A sample of a hydrocarbon is combusted, producing $$4.40\ \mathrm{g} of$$ $$\mathrm{CO}_2$$ and $$1.80\ \mathrm{g} of$$ $$\mathrm{H}_2\mathrm{O}. $$What is the empirical formula of the hydrocarbon?

Accepted Answer

$$\mathrm{CH}_4$$

Question 3

Which of the following is NOT a diatomic element in its natural state?

Accepted Answer

Nitrogen

Question 4

What is the formula weight of $$\mathrm{Al}_2\mathrm{O}_3 ($$aluminum oxide)? (Atomic weights: Al = 27.0, O = 16.0)

Accepted Answer

$$102.0\ \mathrm{amu}$$

Question 5

A reaction has a theoretical yield of $$10.0\ \mathrm{g}$$ and an actual yield of $$7.5\ \mathrm{g}. $$What is the percent yield?

Accepted Answer

$$75\%$$

Question 6

Which of the following best describes a combustion reaction?

Accepted Answer

A reaction in which a hydrocarbon reacts with $$\mathrm{O}_2 to $$produce $$\mathrm{CO}_2$$ and $$\mathrm{H}_2\mathrm{O}.$$

Question 7

How many molecules are present in $$18.0\ \mathrm{g} of $$water ($$\mathrm{H}_2\mathrm{O}$$)? (Molar mass of $$\mathrm{H}_2\mathrm{O} = 18.0\ \mathrm{g/mol})$$

Accepted Answer

$$6.02 	imes 10$$^{23}$$

Question 8

If $$4.0\ \mathrm{mol} of$$ $$\mathrm{NH}_3$$ are produced from the reaction $$N_2 + 3H_2$$ \rightarrow 2NH_3$$, how many moles of $$\mathrm{H}_2$$ were consumed?

Accepted Answer

$$6.0\ \mathrm{mol}$$

Question 9

A student mixes $$10.0\ \mathrm{g} of$$ $$\mathrm{CaCl}_2 ($$molar mass $$110\ \mathrm{g/mol}) $$with $$10.0\ \mathrm{g} of$$ $$\mathrm{Na}_2\mathrm{CO}_3 ($$molar mass $$106\ \mathrm{g/mol}) in $$water. The reaction is $$\mathrm{CaCl}_2 + \mathrm{Na}_2\mathrm{CO}_3 \rightarrow 2\mathrm{NaCl} + \mathrm{CaCO}_3. $$What is the limiting reactant?

Accepted Answer

$$\mathrm{Na}_2\mathrm{CO}_3$$

Question 10

Which of the following statements about balancing chemical equations is correct?

Accepted Answer

You may only change the coefficients to balance the equation.

Question 11

How many grams of $$\mathrm{CO}_2$$ are produced from the complete combustion of $$44.0\ \mathrm{g} of $$propane ($$\mathrm{C}_3\mathrm{H}_8$$, molar mass $$44.0\ \mathrm{g/mol}$$)? The balanced equation is $$\mathrm{C}_3\mathrm{H}_8 + 5\mathrm{O}_2 \rightarrow 3\mathrm{CO}_2 + 4\mathrm{H}_2\mathrm{O}.$$

Accepted Answer

$$132.0\ \mathrm{g}$$

Question 12

Which of the following best describes the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that determines the maximum amount of product formed.

Question 13

A compound contains only nitrogen and oxygen. If a $$2.00\ \mathrm{g}$$ sample contains $$1.22\ \mathrm{g} of $$oxygen, what is the empirical formula? (Atomic masses: N = 14.0, O = 16.0)

Accepted Answer

$$\mathrm{NO}_2$$

Question 14

Which of the following conversions is NOT possible in a single step using only the molar mass?

Accepted Answer

Grams to molecules

Question 15

A reaction has the following balanced equation: $$2\mathrm{KClO}_3 \rightarrow 2\mathrm{KCl} + 3\mathrm{O}_2. If$$ $$12.25\ \mathrm{g} of$$ $$\mathrm{KClO}_3 ($$molar mass $$122.5\ \mathrm{g/mol}) $$decomposes, how many grams of $$\mathrm{O}_2 ($$molar mass $$32.0\ \mathrm{g/mol}) $$are produced?

Accepted Answer

$$1.60\ \mathrm{g}$$

Question 16

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

Accepted Answer

Grams of given $$\rightarrow$$ moles of given $$\rightarrow$$ moles of unknown $$\rightarrow$$ grams of unknown

Question 17

Which of the following statements is TRUE regarding the calculation of percent composition?

Accepted Answer

Percent composition is calculated by dividing the atomic weight of each element times the number of atoms by the formula weight of the compound, then multiplying by 100%.

Question 18

A student claims that the number of moles of reactants must always equal the number of moles of products in a balanced chemical equation. Is this statement correct?

Accepted Answer

No, because the number of moles can differ as long as the number of atoms of each element is conserved.

Stoichiometry and Chemical Reactions: Study Notes for General Chemistry

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