Question

Problem 3. n chromium(II) oxide, CrO, is obtained from pure elements, the composition of solid is actually Cro9201.00, and the compound is electrically neutral, and don't conduct electricity. Provide an explanation for this fact.

Answer 1

The compound is electrically neutral. It means total number of positive charges is equal to total number of negative charges. The charge on O ions is -2. Some Cr ions have charge of +2. Some Cr ions have charge of +3. For 100 oxide ions, there are 76 Cr(II) ions and 16 Cr(III) ions. Total 92 chromium ions are present for 100 oxide ions. This gives formula $Cr_{0.92}O_{1.00}$ .

Total charge on 100 oxide ions $=-2 \times 100 = -200$

Total charge on 76 Cr(II) ions $=+2 \times 76 =+152$

Total charge on 16 Cr(III) ions $=+3 \times 16 =+48$

Total positive charges $=+152+48=+200$

Thus total charges cations is equal to total charges on anions. This maintains electrical neutrality.