directed number

Numbers such as minus 2 plus 2 which has specifically stated direction are called directed number.

Example

- add up -2 -3 +2

Solution

-2 +2 -3 = +2-5 =4

- Divide 8 by 2

Solution

8/2 = 4

- Subtract 2 from 8

Solution

8-2 = 6

- Multiply 3 x -2

Solution

3 x -2 = -6

## Finding the oxidation number of a particular element in a given compound

Oxidation number is the combining power of an element relative to itself or other element in a group.

Finding the oxidation number of an element there rule governing it you must first adhere to the rule before you can get accurately the oxidation number of any element.

Rule 1

The oxidation number of an atom in its standard state is zero.

For example

Na, Cl, H, O, Cr, Ba, Ca, and N etc

The full name of the above element are, sodium, chlorine, hydrogen, oxygen, chromium, barium, calcium, and nitrogen.

Rule 11

The oxidation number of a charged species is equal to the charge it bears.

For example

Na+ = +1

Cl- = -1

NH4+ = +1

SO42- = -2

NO3- = -1

Work example

- What is the oxidation number of N in [NH4]+1 if H = -1?

Solution

Let N = x

NH4+ = +1

X + 4(-1) = +1

X – 4 = +1

X – 4+4 = +1 + 4

X = +5

Oxidation number of N = +5

- What is the oxidation number of S in SO42- if O = -2.

Let the oxidation number of S = x

[SO4] = -2

[X – 4x -2] = -2

X – 8 = -2

The oxidation number of S = +6

Rule lll

An oxidation number is a number assigned to an atom or an iron to describe it relative state of oxidation or reduction. The oxidation numbers of all the atoms in a compound must add up to zero.

For example

H2O = 0

Solution

+2-2=0

Etc.

Source from everyday chemistry by john A Oyelese

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