# IMAT 2018 Q41 [Oxidation States]

Compounds of chlorine include:

Cl_2O
KCl
KClO
KClO_3
KClO_4
Cl_2O_7

Which one of the following options correctly lists the oxidation states of chlorine that are shown in these compounds?

A. –1, +1, +5 and +7 only
B. –1, 0 and +1 only
C. –1 only
D. –1, 0, +1, +5 and +7 only
E. –1, +1, +3, +5 and +7 only

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To solve, find the oxidative states of the other molecules in the compound, sum them, and then Chlorine’s charge will be equal to the opposite charge of that number (i.e if other molecules summed charged = -1, then chlorine will have a charge of +1. Why? In neutral compounds, the total oxidative number must be equal to 0).

Cl_2O : Oxygen is a group 6 non metal, and will have an oxidative state of -2. Cl_2 - 2 = 0

Cl_2 = +2

Cl = +1

KCl : Potassium is a group 1 alkali metal, and will have an oxidative state of +1

Cl = -1

KClO : Potassium has an oxidative state of +1, oxygen has an oxidative state of -2.

1 + Cl - 2 = 0

Cl = +1

KClO_3 : Potassium has an oxidative state of +1, oxygen has an oxidative state of -2.

1 + Cl + (3)(-2) = 0

Cl - 5 = 0

Cl = 5

KClO_4 : Potassium has an oxidative state of +1, oxygen has an oxidative state of -2.

1 + Cl + (4)(-2) = 0

Cl - 7 = 0

Cl = +7

Cl_2O_7 : oxygen has an oxidative state of -2.

Cl_2 + (7)(-2) = 0

Cl = +7

\fcolorbox{red}{grey!30}{Therefore the answer is D, \$-1, 0, +1, +5, +7\$}