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Flashcards in redox Deck (25):
1

Define an oxidation half reaction.

An oxidation half reaction is one where electrons are lost in a redox reaction.

2

Define reduction half reaction.

A reduction half reaction is one where electrons are gained in a redox reaction.

3

Define oxidizing agent.

An oxidizing agent is a chemical that gains electrons over the course of a redox reaction. An oxidizing agent causes a different chemical to be oxidized.

4

Define reducing agent.

A reducing agent is a chemical that loses electrons over the course of a redox reaction. A reducing agent causes a different chemical to be reduced.

5

Define oxidation number.

Oxidation number (O.N.) represents either the apparent or actual charge of an atomic particle.

In the case of a monoatomic ion (e.g. Mg2+) the oxidation number is the actual charge.

In the case of a molecular compound (e.g. SO2), then the oxidation number represents the apparent charge. For SO2, the oxygen has an oxidation number of -2 and the sulfur +4. This type of apparent charge is the result of unequal sharing of electrons in covalent bonds of a molecule, where it is as if oxygen was given all of the electrons.

6

What is the oxidation number of an individual atom in a free element?

The oxidation number of an individual atom of a free element = 0. Therefore N2, Cl2, Fe, Hg, C all have oxidation numbers = 0.

7

What is the oxidation number of a monoatomic ion?

The oxidation number of a monoatomic ion is equal to the charge of the ion. Therefore Na+ has an oxidation number = +1; S2- has an oxidation number = -2.

8

What is usually the oxidation number of hydrogen in a compound?

Hydrogen usually has an oxidation number = +1. An exception to this (which is uncommon in the CHEM 112 course) is if hydrogen is the anion in an ionic compound. Therefore in LiH, hydrogen has an oxidation number = -1.

9

What is usually the oxidation number of oxygen in a compound?

Oxygen usually has an oxidation number = -2. An exception is this (which is uncommon in the CHEM 112 course) is when oxygen is in a peroxide compound. For instance in hydrogen peroxide (H2O2), hydrogen has priority over oxygen and has an oxidation number of +1. This means, in this unique case, that oxygen must have an oxidation number of -1.

10

Why is it important to know if you have an ionic compound in determining oxidation numbers?

It is very important to know if you are working with an ionic compound! If you are, you must separate the compound into the individual ions.

Any monoatomic ions will have oxidation numbers equal to the charge of the ion. For example the ionic compound Na2CO3 consists of Na+ ions and CO32- ions. The Na+ ions have oxidation number = +1. For the CO32-, one can assign oxygen to have an oxidation number = -2 and therefore the carbon must be +4 (+4 - 3(-2) = -2). Without realizing this compound as ionic, one could not successfully assign oxidation numbers to the sodium nor the carbon.

11

What is the oxidation number for Zn?

Zn consists of individual atoms in a free element therefore the oxidation number = 0.

12

What is the oxidation number for Zn in ZnCl2?

ZnCl2 is an ionic compound. The monoatomic ion (Zn2+) has an oxidation number = +2.

13

What is the oxidation number for Cl in ZnCl2

ZnCl2 is an ionic compound. The monoatomic ion (Cl-) has an oxidation number = -1.

14

What is the oxidation number for Zn in ZnSO4?

ZnSO4 is an ionic compound. The monoatomic ion (Zn2+) has an oxidation number = +2.

15

What is the oxidation number for O in ZnSO4?

Oxygen (O) is part of the polyatomic anion SO42-. As is typically the case, oxygen has the oxidation number = -2.

16

What is the oxidation number for S in ZnSO4?

Sulfur (S) is part of the polyatomic anion SO42-. Sulfur must have an oxidation number = +6 (+6 - 4(-2) = -2).

17

In a chemical reaction zinc is changed from ZnCl2 to Zn. Has zinc been oxidized or reduced?

Zinc is reduced as electrons are gained in converting Zn+2 to Zn (zero oxidation number).

18

In the chemical reaction:      2HCl + Zn → ZnCl2 + H2, which chemical is the reducing agent.

Zn is the reducing agent as it loses electrons (to become Zn2+) and reduce H in HCl to H2.

19

Is the following statement true or false: metal elements can only be reducing agents in redox reactions.

True statement. Metal elements in redox can only lose electrons to become cations.

20

If molecular oxygen (O2) is involved in a redox reaction, is it likely to behave as an oxidizing agent or a reducing agent?

Molecular oxygen (O2) will typically behave as an oxidizing agent. The oxidation states that we know for oxygen are -2 (and -1 in peroxides), therefore in changing from zero oxidation number to a negative oxidation number, electrons must be gained (which is the role of an oxidizing agent).

21

Half reaction where electrons are lost in a redox reaction.

An oxidation half reaction

22

Half reaction where electrons are gained in a redox reaction.

Reduction half reaction

23

A chemical that gains electrons over the course of a redox reaction.

Oxidizing agent

24

A chemical that loses electrons over the course of a redox reaction. 

Reducing agent

25

Represents either the apparent or actual charge of an atomic particle.

 

Oxidation number