`you have to be careful about pouring drano down your pipes since it is mainly hydrochloric acid--you can't do it if they are made of aluminum because it will dissolve them! you can't acid clean your aluminum auto parts for the same reasons: 2 al + 6 hcl → 2 alcl3 + 3h2. if you wanted to make 10.0 moles of hydrogen gas, how many many moles of al would you need? note: all numbers located immediately after elemental symbols should be considered subscripts.