How many millilitres of 85% (w/w) phosphoric acid having a density of 1.71 g/ml should be used in preparing 3.8L of 0.25% (w/v) phosphoric acid solution to be used for bladder irrigation? (3 marks)

0.25% w/v -> 0.25 g/100ml -> 2.5 g/1L

X 3.8 -> 9.5 g of phosphoric acid in 3.8L solution.

85% w/w -> 85g/100g

X 9.5/85 -> 9.5 g / 11.18g

Density of phosphoric acid 1.71 g/ml

11.18/1.71 = 6.54 ml