Chromium can show different valencies in compounds with Oxygen – II, III, VI. Draw up the formulas

Chromium can show different valencies in compounds with Oxygen – II, III, VI. Draw up the formulas of the possible oxides of Chromium and compare the mass fraction of Chromium in these oxides.

Let’s compose the corresponding formulas of oxides: chromium (II) oxide – CrO, chromium (III) oxide – Cr2O3, chromium (VI) oxide – CrO3.
We find the mass fraction in oxides by the general formula w = n * Ar (Cr) / Mr (oxide), where n is the number of chromium atoms, Ar (Cr) –
relative atomic mass of chromium (52), Mr (oxide) – relative molecular weight of oxide (resp. 68, 152, 100).

wCr (CrO) = 52/68 = 0.765 * 100% = 76.5%
wCr (Cr2O3) = 52 * 2/152 = 0.684 * 100% = 68.4%
wCr (CrO3) = 52/100 = 0.52 * 100% = 52%