Question

What is the oxidation number of chromium in k2cr2o7

Answer 1

The oxidation number of chromium in K2Cr2O7 (potassium dichromate) is +6. This is determined by knowing that potassium has an oxidation number of +1, oxygen has an oxidation number of -2, and the sum of the oxidation numbers of the chromium atoms must balance the charge contributed by potassium and oxygen to make the compound neutral.

Step-by-step explanation:

The oxidation number of chromium in K2Cr2O7 requires some calculation using the rules of oxidation states. Firstly, potassium (K) has an oxidation number of +1, and each oxygen (O) has an oxidation number of -2. In the compound K2Cr2O7, there are two potassium atoms contributing a total of +2 to the charge of the compound. There are seven oxygen atoms each contributing -2, for a total of -14. Since the compound is neutral overall, the sum of the oxidation numbers of the chromium atoms must balance the negative charge contributed by the oxygen. Therefore, the total oxidation state for the two Cr atoms must be +12 in order to have a net charge of zero when added to the oxidation states of potassium and oxygen. Dividing this by two, since there are two chromium atoms, gives an oxidation number of +6 for each chromium atom.

Additionally, in the reduction half-reaction, Cr2O72- is reduced to Cr3+ with each chromium atom being in the +6 oxidation state initially. The chemical reaction involving the conversion of Fe2+ to Fe3+ supported by potassium dichromate provides further evidence that each chromium atom has an initial oxidation state of +6.

Answer 2

• The oxidation state of chromium in K₂Cr₂O₇ is 6⁺ (i.e. + 6).

Step-by-step explanation:

You can calculate the oxidation number of most elements following some simple rules.

This is how you do it for chromium in K₂Cr₂O₇.

1) Rule: in a neutral compound the net oxidation number is zero (0).

Hence, sum of the oxidation numbers of K, Cr and O in K₂Cr₂O₇ is 0.

2) Rule: The most common oxidation number of oxygen in compounds, except in peroxides, is 2 ⁻ (negative 2).

3) Rule: the most common oxidation state of alkali metals is 1⁺ (positive 1)

4) Rule: multiply each oxidation state by the corresponding number of atoms in the compound (the subscripts)

• 2(1⁺) + 2(x) + 7(2⁻) = 0

↑ ↑ ↑

K Cr O

• 2 + 2x - 14 = 0

• 2x - 12 = 0

• 2x = 12

• x = 6

Hence, the oxidation number of chromium in this compound is 6⁺.