calculate the mass of the given element in each of the following compounds?

Question

a)bromine in 50.0g of potassium bromide, KBr
b)chromium in 1.00 Kg of sodium dichromate, Na2Cr2O7
c)nitrogen in 85.0g of the amino acid lysine, C6H14N2O2
d)cobalt in 2.84g of cobalt (II) acetate, Co(C2H3O2)2

Answer 1

I'll start you off.

For Br in KBr: mass x Ar/Mr

So it's 50 x 80/(39 + 80)

Now you can do the rest!