Question

A laboratory has a 2.0-mol sample of pure selenium and a 2.0-mol sample of pure chromium. How many more grams of selenium than chromium does this represent?

A) 65.5 g
B) 53.9 g
C) 27.0 g
D) 13.5 g

Answer 1

Δm=2*(M(Se)-M(Cr))
Δm=2*(78.96-52.00)≈53.9 g

B) 53.9 g

Answer 2

B. 53.9

With my periodic table the math works out to:

2 mol Se * (79.0g Se/1 mol Se)= 158.0g Se

2 mol Cr * (52.0g Cr/1 mol Cr)= 104.0g Cr

158.0g Se - 104.0g Cr = 54.0g