Q: Which of the following is the correct calculation for the percent by mass of nitrogen in $$\mathrm{NH}_4\mathrm{NO}_3 ($$molar mass = 80.0 g/mol)? (Atomic mass of N = 14.0 g/mol)

$$\frac{28.0}{80.0} \times 100\%$$

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 g of $$\mathrm{CO}_2$$ and 1.80 g of $$\mathrm{H}_2\mathrm{O}. $$What is the empirical formula of the hydrocarbon?

Accepted Answer

$$\mathrm{CH}_3$$

Question 3

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

Accepted Answer

You must balance equations by adjusting coefficients only.

Question 4

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

Accepted Answer

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

Question 5

Which of the following is a decomposition reaction?

Accepted Answer

$$2\mathrm{KClO}_3 \rightarrow 2\mathrm{KCl} + 3\mathrm{O}_2$$

Question 6

A reaction has a theoretical yield of 10.0 g, but only 7.5 g of product is actually obtained. What is the percent yield?

Accepted Answer

$$75\%$$

Question 7

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

Accepted Answer

Sulfur

Question 8

If 5.0 g of $$\mathrm{NaCl} ($$molar mass = 58.5 g/mol) is dissolved in water, how many moles of $$\mathrm{NaCl}$$ are present?

Accepted Answer

$$0.0855$$ mol

Question 9

A student mixes 10.0 g of $$\mathrm{N}_2 ($$molar mass = 28.0 g/mol) with 10.0 g of $$\mathrm{H}_2 ($$molar mass = 2.0 g/mol) to produce ammonia ($$\mathrm{NH}_3) $$according to the equation: $$\mathrm{N}_2 + 3\mathrm{H}_2 \rightarrow 2\mathrm{NH}_3. $$What is the limiting reactant?

Accepted Answer

$$\mathrm{N}_2$$

Question 10

Which of the following best describes the relationship between formula weight and molar mass?

Accepted Answer

Formula weight and molar mass have the same numerical value but different units.

Question 11

How many grams of $$\mathrm{CO}_2$$ are produced when 44.0 g of $$\mathrm{CH}_4 ($$molar mass = 16.0 g/mol) is completely combusted? (Balanced equation: $$\mathrm{CH}_4 + 2\mathrm{O}_2 \rightarrow \mathrm{CO}_2 + 2\mathrm{H}_2\mathrm{O}$$; molar mass of $$\mathrm{CO}_2 = 44.0 g/$$mol)

Accepted Answer

44.0 g

Question 12

Which of the following steps is NOT necessary when determining the empirical formula from percent composition?

Accepted Answer

Multiply the percent composition by Avogadro's number.

Question 13

A reaction mixture contains 0.50 mol of $$\mathrm{A}$$ and 1.0 mol of $$\mathrm{B}$$ for the reaction $$\mathrm{A} + 2\mathrm{B} \rightarrow \mathrm{C}. $$What is the maximum number of moles of $$\mathrm{C}$$ that can be formed?

Accepted Answer

0.50 mol

Question 14

Which of the following is the correct formula for magnesium nitride, given that magnesium forms $$\mathrm{Mg}^{2+}$$ ions and nitride is $$\mathrm{N}^{3-}$$?

Accepted Answer

$$\mathrm{Mg}_3\mathrm{N}_2$$

Question 15

Which of the following best describes a combustion reaction?

Accepted Answer

A reaction in which a compound containing C and H reacts with $$\mathrm{O}_2 to $$form $$\mathrm{CO}_2$$ and $$\mathrm{H}_2\mathrm{O}.$$

Question 16

If you have 3.0 mol of $$\mathrm{O}_2$$, how many molecules of $$\mathrm{O}_2 do $$you have?

Accepted Answer

$$1.81 	imes 10$$^{24}$$

Question 17

A chemist reacts 2.0 mol of $$\mathrm{Al}$$ with 3.0 mol of $$\mathrm{Cl}_2 to $$form $$\mathrm{AlCl}_3$$ according to the equation: $$2\mathrm{Al} + 3\mathrm{Cl}_2 \rightarrow 2\mathrm{AlCl}_3. $$What is the limiting reactant?

Accepted Answer

Neither; both are present in stoichiometric amounts

Question 18

Which of the following is the correct calculation for the percent by mass of nitrogen in $$\mathrm{NH}_4\mathrm{NO}_3 ($$molar mass = 80.0 g/mol)? (Atomic mass of N = 14.0 g/mol)

Accepted Answer

$$\frac{28.0}{80.0} 	imes 100\%$$

Question 19

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

Accepted Answer

Grams to molecules

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