Sciencemadness Discussion Board

Making nitrosulfuric acid

dangerous amateur - 5-11-2015 at 13:24

What is the best way to do it, with minimal heating and decomposition?

95% sulfuric and 55% nitric as starting materials.

Since sulfuric acid is the stronger one i would pour nitric acid slowly into the sulfuric.

Is that the optimal process, or would you do it the other way round, and why?

Detonationology - 5-11-2015 at 13:36

A nitrating solution is commonly composed of ~3:1 ratio of 98% sulfuric to 68% nitric acid. No, the rule of thumb when it comes to acid is Always add acid to water (slowly). Never the opposite with very concentrated acids. The reason is because the reaction of a strong acid (or even a strong base) in water can be very exothermic and cause the acid to flash boil, spewing acid... and that's never a pleasant day, is it.

annaandherdad - 5-11-2015 at 13:48

Quote: Originally posted by Detonationology  
No, the rule of thumb when it comes to acid is Always add acid to water (slowly).


Of course I know this rule but I have never seen that it was necessary except with sulfuric acid. Concentrated hydrochloric acid, for example, does release some energy on dilution, but it's nowhere near enough to cause any flash boiling, nor does standard 68% nitric acid. I admit I've never tried concentrated (95% or more) nitric acid or phosphoric acid etc, don't know about these.

Detonationology - 5-11-2015 at 13:57

Quote: Originally posted by annaandherdad  
Quote: Originally posted by Detonationology  
No, the rule of thumb when it comes to acid is Always add acid to water (slowly).


Of course I know this rule but I have never seen that it was necessary except with sulfuric acid. Concentrated hydrochloric acid, for example, does release some energy on dilution, but it's nowhere near enough to cause any flash boiling, nor does standard 68% nitric acid. I admit I've never tried concentrated (95% or more) nitric acid or phosphoric acid etc, don't know about these.

You are probably right, and I've never had any problems, but it sounds like there is a fair amount of water in the nitric acid to consider before dumping it into some sulfuric acid.

woelen - 6-11-2015 at 00:58

Never add conc. nitric acid to H2SO4 (nor conc. HCl). These acids contain a lot of water and this will produce a lot of heat with H2SO4. You should add the H2SO4 to the other acids. With HCl there is the added issue that the released HCl is a gas and hence there is even more expansion and the risk of splashing around conc. H2SO4 is even larger with that.

Adding water to conc. HNO3 (max. 70%) or conc. HCl is not a real problem, hardly any heat is produced. Adding water to fuming nitric acid, however, also is dangerous. This should be done the other way around.

dangerous amateur - 7-11-2015 at 04:51

Thank you guys.

chornedsnorkack - 8-11-2015 at 08:25

Quote: Originally posted by woelen  

Adding water to conc. HNO3 (max. 70%) or conc. HCl is not a real problem, hardly any heat is produced. Adding water to fuming nitric acid, however, also is dangerous. This should be done the other way around.


Does it mean that fuming nitric acid (because of its low water concentration) can be added to concentrated sulphuric acid?

Also, does HCl dissolve in fuming nitric acid, or does addition of fuming nitric acid to concentrated HCl always drive HCl off by binding the water, even if flash heating is avoided?