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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