In which compound does chlorine have the highest oxidation number?

6 Answers

• You just have to follow oxidation rules.

  First rule that applies is that K (a group 1A metal) always has an oxidation state of +1

  Second rule that applies is that O (in this type of compound) always has an oxidation state of -2

  Third rule is that the oxidation state of a polyatomic must equal the charge of the polyatomic ion.

  In hypochlorite (ClO-) the sum of the oxidation states must equal -1. If Oxygen has a -2 state, Cl must have a +1 oxidation number.

  In chlorite (ClO2-), the sum also equals -1, so if O has a -2 and there are two of them for a total -4, Cl must have a +3 oxidation state.

  You can see the oxidation state of Cl gets higher as more O is added, so with 4 oxygen KClO4 has the highest Cl oxidation state. 4 (-2) = -8 oxygen, so Cl would be +7.

  Hope that helps!

• It's easy to find the oxidation number for Cl since you know the oxidation numbers for K and O. K is always +1 and O is always -2 (unless it's peroxide, which is -1).

  a) KClO . . .in any compound, the sum of the oxidation numbers must be zero.

  So, ox. no. K + ox. no. Cl + ox. no. O = 0

  . . . . .+1 . . .+ ox. no. Cl + . . .-2 . . = 0

  ox. no. Cl = +1

  b) KClO2 . . .here we have 2 O, so the ox. no. of 2 O = 2 x -2 = -4

  +1 + ox. no. Cl + (-4) = 0

  ox. no. Cl = +3

  For c) and d), the oxidation numbers for Cl are 5 and 7, respectively.

• d, KClO4.

  What you do is look at the common oxidation numbers for the other elements in the compound. In this case, K is always +1, and O is usually -2. From there, you can work out what oxidation number Cl should have - it is +7 in the case of KClO4, and that's the highest oxidation number Cl can attain.

• In (d) the K is +1, and each O is -2, the without the Cl we have -7. So the Cl must be +7 to make the whole compound zero.

• So would this answer not change if the answer choices were NaClO, NaClO2, NaClO3, and NaClO4?

• (mass of O)(# of O) divided by (molecular formula)

  answer is d