Question 1

Which of the following is NOT a valid piece of evidence that a chemical reaction has occurred?

Accepted Answer

A decrease in temperature without any other observable change

Question 2

Consider the reaction: $$2 \mathrm{Al}(s) + 6 \mathrm{HCl}(aq) \rightarrow 2 \mathrm{AlCl}_3(aq) + 3 \mathrm{H}_2(g). If $$you start with 10.0 g of Al and 20.0 g of HCl, which is the limiting reactant?

Accepted Answer

Hydrochloric acid (HCl)

Question 3

A 25.0 mL sample of pure ethanol ($$\mathrm{CH}_3\mathrm{CH}_2\mathrm{OH}$$, density $$0.789\ \mathrm{g/mL}) is $$dissolved to make 250 mL of solution. What is the molarity of ethanol in the solution? (Molar mass of ethanol = $$46.07\ \mathrm{g/mol})$$

Accepted Answer

$$0.857\ \mathrm{M}$$

Question 4

Which of the following best describes the law of conservation of mass as it applies to chemical reactions?

Accepted Answer

The total number of atoms of each element must be the same on both sides of the equation.

Question 5

A solution is prepared by dissolving $$4.85\ \mathrm{g} of$$ $$\mathrm{K}_2\mathrm{CrO}_4 ($$molar mass $$194.18\ \mathrm{g/mol}) in $$enough water to make $$250.0\ \mathrm{mL} of $$solution. What is the molarity of the solution?

Accepted Answer

$$0.100\ \mathrm{M}$$

Question 6

In the reaction $$2\mathrm{C}_8\mathrm{H}_{18}(l) + 25\mathrm{O}_2(g) \rightarrow 16\mathrm{CO}_2(g) + 18\mathrm{H}_2\mathrm{O}(g)$$, how many moles of $$\mathrm{CO}_2$$ are produced from $$4.00$$ moles of $$\mathrm{C}_8\mathrm{H}_{18}$$ and excess $$\mathrm{O}_2$$?

Accepted Answer

$$16.0$$ moles

Question 7

A $$0.500\ \mathrm{M}$$ solution of $$\mathrm{CaCl}_2 is $$mixed with a $$0.200\ \mathrm{M}$$ solution of $$\mathrm{HCl}. If$$ $$500\ \mathrm{mL} of$$ $$\mathrm{CaCl}_2$$ and $$200\ \mathrm{mL} of$$ $$\mathrm{HCl}$$ are combined, what is the final molarity of $$\mathrm{Cl}^-$$ ions in the resulting $$700\ \mathrm{mL}$$ solution?

Accepted Answer

$$0.429\ \mathrm{M}$$

Question 8

Which of the following statements about limiting reactants is TRUE?

Accepted Answer

The limiting reactant is the one that is completely consumed first.

Question 9

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

Accepted Answer

$$75\%$$

Question 10

A $$1.75\ \mathrm{L}$$ sample of nitrogen gas at STP contains how many moles of $$\mathrm{N}_2$$? (Molar volume at STP = $$22.42\ \mathrm{L/mol})$$

Accepted Answer

$$0.0780$$ mol

Question 11

In the reaction $$4\mathrm{KO}_2(s) + 2\mathrm{CO}_2(g) \rightarrow 2\mathrm{K}_2\mathrm{CO}_3(s) + 3\mathrm{O}_2(g)$$, if $$0.979$$ mol of $$\mathrm{CO}_2$$ reacts and $$1.128$$ mol of $$\mathrm{O}_2 is $$produced, what is the extent of reaction $$\xi$$?

Accepted Answer

$$0.376$$ mol

Question 12

A $$0.250\ \mathrm{M}$$ solution of $$\mathrm{K}_2\mathrm{CrO}_4 is $$prepared. What mass of $$\mathrm{K}_2\mathrm{CrO}_4 ($$molar mass $$194.18\ \mathrm{g/mol}) is $$needed to make $$200.0\ \mathrm{mL} of $$this solution?

Accepted Answer

$$9.71\ \mathrm{g}$$

Question 13

If $$2.00\ \mathrm{mol} of$$ $$\mathrm{CaCO}_3$$ decomposes completely at STP, what volume of $$\mathrm{CO}_2$$ gas is produced? (Molar volume at STP = $$22.42\ \mathrm{L/mol})$$

Accepted Answer

$$44.84\ \mathrm{L}$$

Question 14

A $$28.0\% (by $$mass) HCl solution has a density of $$1.14\ \mathrm{g/mL}. $$What is the mass of HCl in $$250.0\ \mathrm{mL} of $$this solution?

Accepted Answer

$$79.8\ \mathrm{g}$$

Question 15

Which of the following best describes a synthesis reaction?

Accepted Answer

Two or more substances combine to form a new compound.

Question 16

If $$47.7\ \mathrm{g} of $$urea ($$\mathrm{CO(NH_2$)_2}$$, molar mass $$60.06\ \mathrm{g/mol}) is $$produced from $$1.00\ \mathrm{mol} of$$ $$\mathrm{CO}_2$$, what is the percent yield?

Accepted Answer

$$79.4\%$$

Question 17

A $$0.250\ \mathrm{M}$$ solution of $$\mathrm{K}_2\mathrm{CrO}_4 is to be $$diluted to $$0.0100\ \mathrm{M}$$ using water. What volume of the $$0.250\ \mathrm{M}$$ solution is needed to prepare $$250.0\ \mathrm{mL} of $$the diluted solution?

Accepted Answer

$$10.0\ \mathrm{mL}$$

Chemical Reactions & Stoichiometry: A Study Guide

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