Question

How to prepare 35% perchloric acid from 70% perchloric acid?

Answer 1

M1V1 = M2V2  

(71%)V1 = (35%)V2  

2.02V1 = V2  

thus, whatever volume of the 71% solution you start with, you will need to double its volume by diluting with H2O. NOTE: remember to add the acid slowly to water and NOT water to the acid.