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AP Chemistry Unit 4: Chemical Reactions

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Unit 4: Chemical Reactions

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Question 1

Which of the following describes a precipitation reaction?

HCl (aq) + NaOH (aq) \to NaCl (aq) + H_{2} O (l)

CaC l_{2} (aq) + N a_{2} S O_{4} (aq) \to CaS O_{4} (s) + 2 NaCl (aq)

Zn (s) + CuS O_{4} (aq) \to ZnS O_{4} (aq) + Cu (s)

2 H_{2} O_{2} (l) \to 2 H_{2} O (l) + O_{2} (g)

Question 2

In a balanced redox equation in acidic solution, $Mn O_{4}^{-}$ is reduced to $M n^{2 +}$ while $F e^{2 +}$ is oxidized to $F e^{3 +}$ . How many $F e^{2 +}$ ions are required to reduce one $Mn O_{4}^{-}$ ?

2

3

5

7

Question 3

When a small piece of sodium metal is added to water, bubbles form vigorously and the solution becomes basic. What type of reaction is occurring?

A.Double-displacement (metathesis) reactionB.Combustion reactionC.Single-displacement (redox) reactionD.Acid–base neutralization

Question 4

In the reaction $N_{2} (g) + 3 H_{2} (g) \to 2 N H_{3} (g)$ , if $28.0 g$ of $N_{2}$ and $9.00 g$ of $H_{2}$ are mixed, which is the limiting reagent? (Molar masses: N $_{2}$ = 28.0 g/mol, H $_{2}$ = 2.02 g/mol)

N_{2}

, because it has a higher molar mass.B.

H_{2}

, because more moles of it are required per mole of product.C.

N_{2}

, because comparing moles available to the stoichiometric requirement shows N

_{2}

runs out first.D.Neither; both are present in stoichiometric amounts.

Question 5

When $Cu (s)$ is placed in $AgN O_{3} (aq)$ , which observation is consistent with this single-displacement reaction, and what does the activity series predict?

A.No reaction occurs because Cu is below Ag in the activity series.B.Silver metal deposits on the copper and the solution turns blue as Cu

^{2 +}

forms.C.Copper dissolves and forms

C u_{2} O

, a red solid.D.Silver nitrate decomposes to release

N O_{2}

gas and

O_{2}

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Question 6

How many grams of $H_{2} O$ are produced when $4.00 g$ of $H_{2}$ reacts completely with excess $O_{2}$ ?

$2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (g)$

(Molar masses: H $_{2}$ = 2.02 g/mol, H $_{2}$ O = 18.02 g/mol)

36.0 g

18.0 g

9.00 g

72.1 g

Question 7

Consider a combustion reaction: $C_{3} H_{8} (g) + 5 O_{2} (g) \to 3 C O_{2} (g) + 4 H_{2} O (g)$ . If $44.0 g$ of propane ( $M = 44.1 g/mol$ ) reacts with $128 g$ of $O_{2}$ ( $M = 32.0 g/mol$ ), which is the limiting reagent?

C_{3} H_{8}

, because its mass is smaller.B.

O_{2}

, because 5 moles are needed per mole of propane but only 4 moles of O

_{2}

are available.C.

C_{3} H_{8}

, because the mole ratio requires more propane than available.D.Neither; both are present in stoichiometric amounts.

Question 8

The theoretical yield of aspirin in a synthesis reaction is $2.70 g$ , but a student collects only $2.16 g$ . What is the percent yield?

80.0%

125%

20.0%

54.0%

Question 9

Assign oxidation numbers and identify the element that is oxidized in the following reaction:

$Zn (s) + 2 HCl (aq) \to ZnC l_{2} (aq) + H_{2} (g)$

A.H is oxidized (changes from

+ 1

0

).B.Zn is oxidized (changes from

0

+ 2

).C.Cl is oxidized (stays at

- 1

).D.Zn is reduced (changes from

0

+ 2

Question 10

A student reacts $10.0 g$ of $CaC O_{3}$ with excess HCl and collects $C O_{2}$ gas. The molar mass of $CaC O_{3}$ is $100.1 g/mol$ . How many moles of $C O_{2}$ are produced?

$CaC O_{3} (s) + 2 HCl (aq) \to CaC l_{2} (aq) + H_{2} O (l) + C O_{2} (g)$

0.100 mol

0.200 mol

1.00 mol

0.0500 mol

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Question 11

When excess $NaOH (aq)$ is added to a solution of $FeC l_{3} (aq)$ , a reddish-brown precipitate forms. The full ionic equation includes $F e^{3 +} (aq) + 3 O H^{-} (aq) \to Fe (OH)_{3} (s)$ . What are the spectator ions?

N a^{+}

and

C l^{-}

F e^{3 +}

and

O H^{-}

N a^{+}

and

F e^{3 +}

C l^{-}

and

O H^{-}

Question 12

Which of the following is the correct net ionic equation for the reaction between aqueous $Pb (N O_{3})_{2}$ and aqueous $KI$ , which forms a yellow precipitate of $Pb I_{2}$ ?

Pb (N O_{3})_{2} (aq) + 2 KI (aq) \to Pb I_{2} (s) + 2 KN O_{3} (aq)

P b^{2 +} (aq) + 2 I^{-} (aq) \to Pb I_{2} (s)

K^{+} (aq) + N O_{3}^{-} (aq) \to KN O_{3} (aq)

P b^{2 +} (aq) + I^{-} (aq) \to Pb I_{2} (s)

AP Chemistry Unit 4: Chemical Reactions — Free with Answer Explanations | Test Practice Hub