I'm working with a delicate experiment whilst trying to test corrosion of stainless-steels in a chloramine environment. I've run into various literature that discusses the formation of different types of chloramines relative to pH and ratios of chlorine to nitrogen (or ammonia). In order to create this environment without being a complete f-bomb and accidentally creating concentrated Nitrogen Trichloride. I'd love some clarification for my non-chemical-based knowledge.

Production of Chloramines

I've read that monochloramine dominates when the chlorine to nitrogen weight ratio in <5:1 (or 1:1 molar ratio). Separate ratios exist for other chloramines but let's focus on this for the purpose of my question.

Firstly, I'm a little confused how to convert between these units. I imagine the 'weight ratio' is measure as PPM or mg/L, while molar ratio is g/mol? I feel like this should be easy but my head's in a twist.

Secondly, separate literature use similar figures for 'chlorine to nitrogen ratio [Cl:N]' whilst other reference 'chlorine to ammonia ratio [Cl:NH3]' (or even chlorine to ammonia-nitrogen). Are these synonymous or should weight of the included hydrogen (albeit minimal) be included?

Tertiary , I'd assume the ratios mentioned above refer to 'free chlorine residual' not total chlorine, which includes chloramines (chorine already bonded to ammonia). Sounds obvious but just checking.

  • $\begingroup$ molar ratio [mol/mol] = weight ratio [g/g] / molar mass ratio[(g/mol)/(g/mol)]. The ratios can be expressed in any compatible form, like molar PPM= mass PPM / molar mass ratio. Important thing is not to ignore proper unit arithmetics. // Nitrogen is synonym to ammonia nitrogen if there is not other nitrogen. Nitrogen is obviously not a synonym for ammonia. Molar ratios are the same for nitrogen and ammonia, but not weight ratios. N has molar mass approx. 14 g/mol, ammonia 17 g/mol. $\endgroup$
    – Poutnik
    Oct 4, 2023 at 4:16
  • $\begingroup$ @Poutnik, thanks working with units directly makes life simpler. I thought it may have been that simple so appreciate the clarification. As a simple Mech. Eng I'll stick with the familiar grams and litres. $\endgroup$
    – Kuhrta
    Oct 4, 2023 at 22:02


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