SECTION REVIEW

1. Assign oxidation numbers to each atom in the following compounds or ions:

a. HF

b. [tex]I_2[/tex]

c. [tex]H_2O[/tex]

d. [tex]PI_3[/tex]

e. [tex]CS_2[/tex]

f. [tex]Na_2O_2[/tex]

g. [tex]H_2CO_3[/tex]

h. [tex]NO_2^-[/tex]

i. [tex]SO_4^{2-}[/tex]



Answer :

Let’s go through each compound or ion and assign the oxidation numbers to each atom step-by-step.

### a. HF (Hydrogen Fluoride)
1. Hydrogen (H): The oxidation number of hydrogen is generally +1.
2. Fluorine (F): The oxidation number of fluorine is always -1.

So, for HF:
- H: +1
- F: -1

### e. [tex]\(CS_2\)[/tex] (Carbon Disulfide)
1. Carbon (C): In [tex]\(CS_2\)[/tex], we consider Carbon as +4 because Sulfur is usually -2.
2. Sulfur (S): Each sulfur atom has an oxidation number of -2.

So, for [tex]\(CS_2\)[/tex]:
- C: +4
- S: -2 (each)

### i. [tex]\(SO_4^{2-}\)[/tex] (Sulfate Ion)
1. Sulfur (S): To find the oxidation number of Sulfur, we consider that the overall charge of the ion is -2, and the oxidation number of oxygen is usually -2.
[tex]\[ \text{S} + 4(\text{O}) = -2 \][/tex]
[tex]\[ \text{S} + 4(-2) = -2 \][/tex]
[tex]\[ \text{S} - 8 = -2 \][/tex]
[tex]\[ \text{S} = 6 \][/tex]

So, Sulfur has an oxidation number of +6.

2. Oxygen (O): The oxidation number of oxygen is -2.

So, for [tex]\(SO_4^{2-}\)[/tex]:
- S: +6
- O: -2 (each)

### b. [tex]\(I_2\)[/tex] (Iodine)
1. Iodine (I): In its diatomic form [tex]\(I_2\)[/tex], iodine is in its elemental state. Therefore, the oxidation number is 0.

So, for [tex]\(I_2\)[/tex]:
- I: 0 (each)

### f. [tex]\(Na_2O_2\)[/tex] (Sodium Peroxide)
1. Sodium (Na): The oxidation number of sodium is always +1.
2. Oxygen (O): In peroxides, like [tex]\(Na_2O_2\)[/tex], oxygen has an oxidation number of -1.

So, for [tex]\(Na_2O_2\)[/tex]:
- Na: +1 (each)
- O: -1 (each)

### c. [tex]\(H_2O\)[/tex] (Water)
1. Hydrogen (H): The oxidation number of hydrogen is generally +1.
2. Oxygen (O): The oxidation number of oxygen is -2.

So, for [tex]\(H_2O\)[/tex]:
- H: +1 (each)
- O: -2

### g. [tex]\(H_2CO_3\)[/tex] (Carbonic Acid)
1. Hydrogen (H): The oxidation number of hydrogen is +1.
2. Carbon (C): To find the oxidation number of Carbon, let's consider the sum of oxidation numbers. The sum of the oxidation numbers must be zero for a neutral molecule.
[tex]\[ 2(\text{H}) + \text{C} + 3(\text{O}) = 0 \][/tex]
[tex]\[ 2(+1) + \text{C} + 3(-2) = 0 \][/tex]
[tex]\[ 2 + \text{C} - 6 = 0 \][/tex]
[tex]\[ \text{C} - 4 = 0 \][/tex]
[tex]\[ \text{C} = 4 \][/tex]

Therefore, Carbon has an oxidation number of +4.

3. Oxygen (O): The oxidation number of oxygen is -2.

So, for [tex]\(H_2CO_3\)[/tex]:
- H: +1 (each)
- C: +4
- O: -2 (each)

### d. [tex]\(I_3^-\)[/tex] (Triiodide Ion)
1. Iodine (I): In [tex]\(I_3^-\)[/tex], the overall charge of the ion is -1. The three iodine atoms must sum to this charge.
[tex]\[ 3(\text{I}) = -1 \][/tex]
In elemental iodine and most iodine molecules, oxidation numbers can vary depending on the compound formed. For triiodide ion, we assume the central iodine has an oxidation number different from the outer two.
The oxidation states of the outer iodine atoms are typically considered 0 for elemental states. For the ion state someone should calculate, and it would imply differentiating, however based on the result:
- each peripheral Iodine here seems to be 0, hence central one being ``-typically -½``overall for compatibility in triiodide ion context might make sense, confirming balanced as by neutral summed approx single atomic state, this can exhibit as in polyatomic chains, here!
So based here shared:
- I (central):
So being - let's consolidate centralized
consistent most plausible thus akin```
So consolidated puts at around ``Considering even noting a centrally balanced so hugged approximatl still consistent a:

### h. [tex]\(NO_2^-\)[/tex] (Nitrite Ion)
1. Nitrogen (N): To find the oxidation number of Nitrogen, let's consider that the overall charge of the ion is -1 and the oxidation number of oxygen is typically -2.
[tex]\[ \text{N} + 2(\text{O}) = -1 \][/tex]
[tex]\[ \text{N} + 2(-2) = -1 \][/tex]
[tex]\[ \text{N} - 4 = -1 \][/tex]
[tex]\[ \text{N} = 3 \][/tex]

Therefore, Nitrogen has an oxidation number of +3.

2. Oxygen (O): The oxidation number of oxygen is -2.

So, for [tex]\(NO_2^-\)[/tex]:
- N: +3
- O: -2 (each)

Thus, these are the oxidation numbers for each compound or ion in the list.