An impure sample of Na2 SO4 has a mass of 1.56 g. This sample is dissolved and allowed to react with BaCl2 solution. The precipitate has a mass of 2.15 g Calculate the percentage purity of Na2 SO4 in the original sample.

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles