Q: A sample of glucose ($$\mathrm{C_6H_{12}O_6$}) $$has a mass of 18.0 g. What is the number of molecules present in this sample? (Molar mass of glucose = $$180.0\ \mathrm{g\ $$mol^{-1}$$})$$

$$6.02 \times 10$$^{22}$$ molecules$

Question 1

A sample of glucose ($$\mathrm{C_6H_{12}O_6$}) $$has a mass of 18.0 g. What is the number of molecules present in this sample? (Molar mass of glucose = $$180.0\ \mathrm{g\ $$mol^{-1}$$})$$

Accepted Answer

$$6.02 	imes 10$$^{22}$$ molecules$

Question 2

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

Accepted Answer

$$\mathrm{CH_2O}$$

Question 3

What is the percent composition by mass of nitrogen in ammonium nitrate ($$\mathrm{NH_4NO_3}$$)? (Atomic masses: N = 14.0, H = 1.0, O = 16.0)

Accepted Answer

35.0\%

Question 4

Which of the following is a correctly balanced equation for the combustion of propane ($$\mathrm{C_3H_8}$$)?

Accepted Answer

$$\mathrm{C_3H_8} + 5\ \mathrm{O_2$} \rightarrow 3\ \mathrm{CO_2$} + 4\ \mathrm{H_2O}$$

Question 5

Which of the following best describes a precipitation reaction?

Accepted Answer

A reaction in which an insoluble solid forms when two solutions are mixed

Question 6

Given the reaction: $$\mathrm{2Al + 3Cl_2 \rightarrow 2AlCl_3}$$, how many grams of $$\mathrm{$$AlCl_3$$}$$ are produced from 10.0 g of aluminum? (Molar masses: Al = 27.0, AlCl$$_3 = 133.5)$$

Accepted Answer

49.4 g

Question 7

Which of the following is the correct net ionic equation for the reaction between aqueous solutions of sodium sulfate and barium chloride?

Accepted Answer

$$\mathrm{Ba$$^{2+}$$(aq) + SO_4$^{2-}(aq) \rightarrow $$BaSO_4$$(s)}$$

Question 8

A student mixes 50.0 g of $$\mathrm{$$CaCl_2$$} ($$molar mass = 111.0 g/mol) with 50.0 g of $$\mathrm{Na_2CO_3} ($$molar mass = 106.0 g/mol) in water. The reaction is: $$\mathrm{$$CaCl_2$$(aq) + Na_2CO_3(aq) \rightarrow $$CaCO_3$$(s) + 2NaCl(aq)}. $$What is the limiting reactant?

Accepted Answer

$$\mathrm{Na_2CO_3}$$

Question 9

If 20.0 g of $$\mathrm{H_2O} is $$produced from the combustion of hydrogen gas, what is the percent yield if the theoretical yield is 22.5 g?

Accepted Answer

88.9\%

Question 10

Which of the following is the correct balanced equation for the reaction of sulfuric acid with sodium hydroxide?

Accepted Answer

$$\mathrm{H_2SO_4} + 2\mathrm{NaOH} \rightarrow \mathrm{Na_2SO_4} + 2\mathrm{H_2O}$$

Question 11

A reaction has an enthalpy change $$\Delta H = -125\ \mathrm{kJ}. $$Which statement is true about this reaction?

Accepted Answer

The reaction is exothermic and releases heat to the surroundings.

Question 12

How many moles of $$\mathrm{O_2$}$$ are required to completely react with 4.0 moles of $$\mathrm{C_2H_6} in $$the reaction: $$\mathrm{2C_2H_6} + 7O_2 \rightarrow 4CO_2 + 6H_2O$$?

Accepted Answer

7.0 moles

Question 13

Which of the following is the correct molecular formula for a compound with empirical formula $$\mathrm{CH_2$}$$ and a molar mass of 56 g/mol?

Accepted Answer

$$\mathrm{C_4H_8}$$

Question 14

A 5.00 g sample of magnesium reacts with excess hydrochloric acid according to $$\mathrm{Mg + 2HCl \rightarrow $$MgCl_2$$ + H_2$}. $$How many liters of $$\mathrm{H_2$}$$ gas at STP (22.4 L/mol) are produced?

Accepted Answer

4.62 L

Question 15

Which of the following is a correct total ionic equation for the reaction of aqueous sodium sulfate with aqueous barium nitrate?

Accepted Answer

$$\mathrm{2Na^+(aq) + SO_4$^{2-}(aq) + Ba$$^{2+}$$(aq) + 2NO_3^-(aq) \rightarrow $$BaSO_4$$(s) + 2Na^+(aq) + 2NO_3^-(aq)}$$

Question 16

A student is asked to write the net ionic equation for the reaction between hydrochloric acid and sodium hydroxide. Which is correct?

Accepted Answer

$$\mathrm{H^+(aq) + OH^-(aq) \rightarrow H_2O(l)}$$

Question 17

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

Accepted Answer

Calculate the moles of product each reactant can produce and identify the smallest value.

Question 18

A reaction has a theoretical yield of 15.0 g and an actual yield of 12.0 g. What is the percent yield?

Accepted Answer

80.0\%

Question 19

Which of the following is the correct balanced equation for the gas evolution reaction between sodium sulfide and hydrochloric acid?

Accepted Answer

$$\mathrm{Na_2S(aq) + 2HCl(aq) \rightarrow 2NaCl(aq) + H_2S(g)}$$

Question 20

A 10.0 g sample of $$\mathrm{$$CaCO_3$$} ($$molar mass = 100.0 g/mol) is heated to produce $$\mathrm{CaO}$$ and $$\mathrm{CO_2$}$$ according to $$\mathrm{$$CaCO_3$$(s) \rightarrow CaO(s) + CO_2$(g)}. $$What mass of $$\mathrm{CO_2$} ($$molar mass = 44.0 g/mol) is produced?

Accepted Answer

4.40 g

Exam 3 Study Guide: Chemical Composition, Reactions, and Stoichiometry

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