What is the oxidation number of chromium in potassium dichromate? 

CONCEPT:

Oxidation Number:

• The oxidation number of an element in a compound is the charge it would have if all bonds were ionic.
• For polyatomic ions, the sum of the oxidation numbers of all atoms equals the charge of the ion.
• Potassium dichromate (K₂Cr₂O₇) contains chromium in a compound where its oxidation number can be determined using the rules for calculating oxidation numbers.

EXPLANATION:

• In potassium dichromate, the formula is K₂Cr₂O₇.
• Potassium (K) has an oxidation number of +1.
• Oxygen (O) has an oxidation number of -2.
• Let the oxidation number of chromium (Cr) be x.
• Using the rule that the sum of oxidation numbers equals the total charge of the compound (which is 0 for neutral compounds):
  • 2(+1) + 2x + 7(-2) = 0
  • 2 + 2x - 14 = 0
  • 2x - 12 = 0
  • 2x = 12
  • x = +6

Therefore, the oxidation number of chromium in potassium dichromate is +6.