If the masses of Cr and O are in the ratio 13:12 in CrO3, then the ratio of O that combines with the same mass of Cr in Cr2O3 and Cr2O7 is
Answers
The equation for the reaction of oxygen and chromium is as follows:
4Cr(s)+3O₂(g)→2Cr₂O₃(s)
We can take a sample of the 2 where we have 13g of Cr and 12 g of O to have a mass ratio of 13:12, for the purpose of calculation.
In the first reaction we will use a mass of oxygen of 12 g.
The reaction of oxygen and Chromium to from dichromate (CrO₇) is:
2Cr + 7O₂ ----------------> 2CrO₇
Mole ratio is 2:7:2
In this case the same amount, 13 g of Cr will be used in this equation.
Calculate the moles of Cr (molar mass = 52)
moles = mass/molar mass
= 13/52
= 0.25 moles
mole ratio between Cr:O₇ is 2:7 , meaning the moles of oxygen will be ( 0.25 × 7/2 = 0.875) moles
Therefore the moles of oxygen are 0.875, calculate the mass using this mole value
mass = moles × molar mass (molar mass of O₂ = 32)
= 0.875 × 28
= 28 g
The mass of oxygen used by same mass, 13 g of chromium to give Cr₂O₇ is 28g
The ratio of the oxygen in the 2 equations then is:
12 g : 28 g (simplify)
The ratio therefore is 3:7.