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Thread: Making for making Nitric Acid, Half Baked, (NO2<->N2O4) --> HNO3

  1. #1 Making for making Nitric Acid, Half Baked, (NO2<->N2O4) --> HNO3 
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    Objective: small scale making of nitric acid of moderate purity with minimal or no controlled chemical precursors. Note that I do not always include H2O in the formulas when I'm writing about principles.

    Nitric acid is unhealthy to ingest, is corrosive and can produce unhealthy gasses. Before handling please refer to appropriate msds.
    In advance I'd like to appologize for this half baked idea, it's something I've been contemplating but never actually done. I'd like input and ideas.

    Nitric acid ca be used for many different things, it can be bought in some countries but is restricted to a varying degree in many others. By "moderate purity" I mean pure enough for use in simple chemical analysis, titration or simple synthesis. It should be relatively free from nitrous acid (HNO2). The goal is not the end product but the actual method for making (aq)HNO3.

    Formation of (NO2<->N2O4)

    Precursors: common air, electricity
    Equipment: High voltage source, low capacity air pump (aquarium), various glassware and hoses, condenser with cooling system

    NO2 and N2O4 exists in equilibrium, N2O4 favoured in cold temperatures (will from here on be written NO2<->N2O4). They can be made from common air by using the an electric spark gap, powered by say a neon transfomrer. Inside the spark nitrogen dioxide will form. If the spark is contained in an airtight container with connectors for air inlet and outlet, a common aquarium air pump could be used to pump air into the container. The output will contain a mixture of air and (NO2<->N2O4). The output can then be run through a condenser, (NO2<->N2O4) will conense to liquid form at ~20c. The air gasses will escape and most of the (NO2<->N2O4) could be collected in a container.

    Q1) Formation of HNO2 and HNO3

    (NO2<->N2O4) can react with water forming a solution of a mixture of (aq)HNO2 and (aq)HNO3.

    Is it enough to simply pour the (NO2<->N2O4) into deionised water (DI water)?
    If not, how is this reaction achieved?

    Q2) Removal of (aq)HNO2

    Wiki suggests that heating the blend of HNO2 and HNO3 would cause the HNO2 to break down NO and more HNO3.
    *NO is a colourless gas, how would one know when the mixture is pure?
    *Heating can also evaporate the HNO3, what's the right temperature?

    Sincerely yours.

    Last edited by heres; June 30th, 2013 at 07:04 PM.
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  3. #2  
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    Thanks for a detailed reply!
    Quote Originally Posted by PhDemon View Post
    NO2 is NOT colourless, I don't know where you got this from, it's very dark brown.
    The correct temperature is not something I would be able to guess at off the top of my head but NO is a hell of a lot more volatile than HNO3 so it probably wouldn't need to be that high.
    I meant to write NO, not NO2, my bad. The question was how do I know when all the NO has been evapourated since NO (contrary to NO2) is colourless. Since you can't see the NO evaporating, there's no visual clue to when it stops.
    Quote Originally Posted by PhDemon View Post
    If you apply high voltage to air you will make NO and ozone... /---/ The ozone produced will oxidise some of the NO to NO2 /---/where did this information come from?
    There's a myriad of videos on youtube of amateurs and professionals making NO2 in a glass container, usually with a spark ladder.
    Quote Originally Posted by PhDemon View Post
    I don't think NO2 will condense to a liquid at 20 C
    I do not like to quote wikipedia but the BP for NO2 is 21c. Running ~0c water through a condenser might get you liquid NO2 but honestly I prefer your idea of bubbling the gas through DI water to collect the gas.

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