w/w percentage
= mass of the pure compound /
total mass of the sample x 100%
70% HNO₃
contains by mass means every 100 g of sample has 70 g of HNO₃.
The mass of solution = 103.8 g
Hence the mass of HNO₃ = 103.8 g x 70%
= 103.8 g x (70 / 100)
= 72.66 g = 72.7 g.
