Chromium is manufactured by heating a mixture of chromium(III) oxide with aluminium powder. Cr2O3(s) + 2Al(s) → 2Cr(s) + Al2O3(s)

a=Calculate the mass of aluminium needed to react with 50 g of Cr2O3.
b=Calculate the mass of chromium produced from 50 g of Cr2O3.
c=Calculate the mass of chromium produced from 5 kg of Cr2O3.
d=Calculate the mass of chromium produced from5 tonnes of Cr2O3.

Note: 1 tonne = 1,000,000 g
Ar: Cr = 52, O = 16, Al = 27

a)

b)

c)

d)            

Explanation:

The reaction is:

Cr₂O₃(s) + 2Al(s) → 2Cr(s) + Al₂O₃(s)    

a) To find the Al mass needed to react with 50 g of Cr₂O₃, we need to calculate the number of moles of Cr₂O₃:

Where:    

: is the mass = 50 g

: is the molar mass = 2*52+3*16 = 152 g/mol

Now, the estoichiometric relation between Cr₂O₃ and Al is 1:2, so:

Hence, the mass of  Al is:

b) The stoichiometric relation from Cr₂O₃ and Cr is 1:2, hence:

Thus, the mass of Cr is:

c) The number of moles of Cr₂O₃ with a mass of 5 kg is:

So, the mass of Cr is:

d) The mass of Cr produced from 5 tonnes of Cr₂O₃ is:

I hope it helps you!