Chapter 11 Practice Test

Question 1

Which statement about oxidation states (or numbers) is not correct?

Answer 1

Because the electronegativity difference can be small, electronegativity is not an important consideration when determining oxidation states.

Question 2

Look at the oxidation numbers assigned for the ammonium ion, NH4+.

NH	+
4
−3 + 4 (+1) = +1
ammonium ion 

Which of the following statements is not correct?

Answer 2

An electron deficient atom such as nitrogen will welcome the four hydrogen atoms because of the electronegativity difference.

Question 3

What are the oxidation numbers for magnesium and oxygen (in that order) in the MgO molecule?

Answer 3

+2, −2

Question 4

Which of the following shows (in the correct order) the oxidation numbers for phosphorous (P) and oxygen (O) in the polyatomic ion PO43−?

Answer 4

+5, −2

Question 5

What is an oxidation state?

Answer 5

It is a charge assigned to an atom. It tells you how many electrons the atom controls in a compound.

Question 6

Which statement best describes the primary limitation of oxidation state (or oxidation number)?

Answer 6

In molecules, electrons are not just in atomic orbitals. They are also in molecular orbitals. Therefore, oxidation states (or numbers) do not necessarily represent the electron reality for each atom.

Question 7

Which statement about oxidation numbers (or states) is not true?

Answer 7

The oxidation number tells you the exact number of electrons that each atom has or is missing

Question 8

Let’s look at the methane molecule, CH4.

We learned that the electronegativity difference between carbon and hydrogen is very slight. Which statement about this molecule is not correct?

Answer 8

There are four (very) polar C–H bonds in the molecule. They are polar towards the carbon atom because carbon is more electronegative

Question 9

Which statement best summarizes the scenarios for when a molecule can have an oxidation state of 0?

Answer 9

A molecule can have an oxidation state of 0 when the molecule consists of only elemental atoms or the composite oxidation state values for the individual atoms add up to 0.

Question 10

Which of the following rules for determining oxidation states (or numbers) is not correct?

Answer 10

Alkaline earth metals normally have an oxidation state of +1.

Question 11

Let’s continue to look at the rules for assigning oxidation states (or numbers). Which of the following rules is not correct?

Answer 11

An oxidation number should add up to the charge on the most electronegative atom in the molecule.

Question 12

What are the oxidation numbers for sulfur and (the total of) the two oxygen atoms in sulfur dioxide, SO2?

Answer 12

4+, 4−

Question 13

Look at the reaction between oxalate and iodate ions 5C2O42-(aq) + 2IOe-(aq) + 12H+(aq) -> 10CO2(g) + I2(aq) + 6H2O(l) Which of the following correctly identifies the oxidizing agent, the reducing agent, the oxidized compound, and the reduced compound

Answer 13

IO3− is the oxidizing agent and the reduced compound. C2O42− is the reducing agent and the oxidized compound

Question 14

Which of the following correctly shows the oxidation numbers for each of the elements in H2PO4−, I2, and Al(OH)4−?

Answer 14

H2PO4−: H = +1, P = +5, O = −2; I2 : I = 0; Al(OH)4− : Al = +3; O = −2; H = +1

Question 15

Which statement about the following redox reaction in acidic solution is not correct?

H2S(aq) + Cr2O72− (aq) → S(s) + Cr3+ (aq)

Answer 15

The final step involves adding oxygen atoms to the left side of the reaction and hydrogen atoms to the right side of the reaction.

Question 16

Which of the following best describes what a redox reaction is?

Answer 16

It is a reaction in which the oxidation state of one element increases and the oxidation state of another element decreases.

Question 17

Which of the following is not a correct rule for determining oxidation states?

Answer 17

Any compound’s component species have oxidation states that add up to zero.

Question 18

Which of the following correctly identifies the oxidizing agent and the reducing agent?

3H2S(aq) + 2NO3−(aq) + 2H +(aq) → 3S(s) + 2NO(g) + 4H2O(l)

Answer 18

H2S is the reducing agent. NO3− is the oxidizing agent.

Question 19

Which of the following correctly identifies the oxidizing agent, the reducing agent, the oxidized substance, and the reduced substance in the reaction?

6Fe2+(aq) + Cr2O72−(aq) + 14H +(aq) → 6Fe3+(aq) + 2Cr3+(aq) + 7H2O(l)

Answer 19

Cr2O72− is the oxidizing agent. Fe2+ is the reducing agent. Fe2+ is the oxidized substance. Cr2O72− is the reduced substance.

Question 20

Which of the following shows the correct oxidation states for iodine, sulfur, and oxygen in the products of this reaction?

10H +(aq) + 8I −(aq) + SO42−(aq) → H2S(aq) + 4I2(aq) + 4H2O(l)

Answer 20

I is 0; S is −2; O is −2

Question 21

Which of the following correctly summarizes the electron transfer in the given reaction?

10H +(aq) + 8I −(aq) + SO42−(aq) → H2S(aq) + 4I2(aq) + 4H2O(l)

Answer 21

I − → I 0; S6+ → S2−

Question 22

Which of the following correctly shows the oxidation numbers for the elements in Mn3(PO4 )2?
(The phosphate ion is written alone as PO43−.)

Answer 22

O = −2; P = +5; Mn = +2

Question 23

Which statement about balancing this simple redox reaction using the half-reaction method is correct?

Cu(s) + Ag+1 (aq) → Cu+2 (aq) + Ag(s)

Answer 23

At the end of the balancing method, the total number of electron transfers for each of the two half-reactions is the same.

Question 24

Which of the following correctly describes the two half-reactions in the redox reaction below?

CuS(s) + NO3− (aq) → Cu2+ (aq) + SO42− (aq) + NO(g)

Answer 24

CuS(s)→ Cu2+ (aq) + SO42− + 8e − is the oxidation step.

NO3− (aq) + 3e −→ NO(g) is the reduction step.

Question 25

Look at the unbalanced redox reaction (in an acidic solution).

S2O32− (aq) + I2(aq) → SO42− (aq) + I − (aq)

Which of the following is not part of the final balanced reaction?

Answer 25

10H2O(l)