Question

Determine the oxidation number of chlorine in each of the following substances:

a. KCLO3
b. Cl2
c. Ca(ClO4)2
d. Cl2O

Answer 1

Answer : The oxidation number of chlorine in
`KClO_3,Cl_2,Ca(ClO_4)_2\text{ and }Cl_2O` are,
`+5,0,+7\text{ and }+1` respectively.

Explanation :

Oxidation number : It represent the number of electrons lost or gained by the atoms of an element in a compound.

Oxidation numbers are generally written with sign (+ and -) first and then the magnitude.

Rules for Oxidation Numbers :

• The oxidation number of a free element is always zero.
• The oxidation number of a monatomic ion equals the charge of the ion.
• The oxidation number of Hydrogen (H) is +1, but it is -1 in when combined with less electronegative elements.
• The oxidation number of oxygen (O) in compounds is usually -2, but it is -1 in peroxides.
• The oxidation number of a Group 1 element in a compound is +1.
• The oxidation number of a Group 2 element in a compound is +2.
• The oxidation number of a Group 17 element in a binary compound is -1.
• The sum of the oxidation numbers of all of the atoms in a neutral compound is zero.
• The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion.

Now we have to calculate the oxidation number of chlorine (Cl) in each of the following substances.

(a)
`KClO_3`

Let the oxidation state of Cl be, 'x'

`(+1)+x+3(-2)=0\\\\x=+5`

Thus, the oxidation state of Cl is, (+5)

(b)
`Cl_2`

The oxidation number of a free element is always zero.

Thus, the oxidation state of Cl is, (0)

(c)
`Ca(ClO_4)_2`

Let the oxidation state of Cl be, 'x'

`(+2)+2[x+4(-2)]=0\\\\x=+7`

Thus, the oxidation state of Cl is, (+7)

(d)
`Cl_2O`

Let the oxidation state of Cl be, 'x'

`2x+(-2)=0\\\\x=+1`

Thus, the oxidation state of Cl is, (+1)

Therefore, the oxidation number of chlorine in
`KClO_3,Cl_2,Ca(ClO_4)_2\text{ and }Cl_2O` are,
`+5,0,+7\text{ and }+1` respectively.

Answer 2

The oxidation number of Cl may vary in each compound. In a, this is a neutral compound which means the overall charge is zero. oxygen has a total of -6, k has +1, so Cl has to be +5. Cl in b has a zero charge. In c, oxygen has -16, Ca has +2 and Cl has to be +7. In d, oxygen has -2 so Cl is +1.