posted by joanna .
calculate the mass given element of each of the following compounds
a) brimine in 50.0 potassium bromide, KBr
b) Chromium in 1.00 kg sodium dichromate Na2Cr2O7
Here is how to do (a). You can do (b) the same way.
The molar mass of KBr is 39.1 + 79.9 = 119.0. I just added the atomic masses of one K and one Br atom.
50.0 g is 50.0/119.0 = 0.420 moles.
The mass of bromine is the sample is 79.9 g/mole* 0.420 moles = 33.6 g