The relationship between ammonia nitrogen content in water and pH value
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Our factory conducts analyses; the ammonia nitrogen level in the gas generation cycle water was 1385 with a pH of 8.31 the day before yesterday, while it was 1573 with a pH of 7.52 yesterday. Is this normal? I think the higher the ammonia nitrogen level, the higher the pH value should be. (The analyst’s operations are fine.)
Ammonia nitrogen refers to the amount of nitrogen present in water in the form of free ammonia (NH3) or ammonium salts (NH4+). It can be said that the proportion of free ammonia to ammonium salts depends on the pH and water temperature; when the pH is high, the proportion of free ammonia is higher, while conversely, the proportion of ammonium salts is higher. If the source of ammonia nitrogen is dissolved ammonium salts of strong acids such as ammonium chloride, the higher the ammonia nitrogen level, the lower the pH.
It is actually still a matter of organic amines and inorganic ammonium; some issues can be identified from these two types of \"amines/ammonium\": inorganic ammonium can affect the pH value of the liquid, while organic amines do not exhibit basic properties, so ammonia nitrogen content cannot be determined based on pH.
Regarding ammonia, the original poster’s understanding is correct, but it’s not the same case for ammonium
Ammonium nitrogen detected in water bodies refers to the sum of free ammonia and ammonium ions. The common detection methods are Nessler’s reagent colorimetry, salicylic acid colorimetry, and ammonia-sensitive electrode method. When ammonium and ammonia coexist in water, the pH value is related to their ratio, that is, the relationship between the composition of the ammoniacal buffer and the pH. If there are other cations in the water, especially hydrogen ions, ammonia combines with those hydrogen ions to form ammonium ； If there is a large amount of hydroxide ions in the water, ammonium ions will partially or completely dissociate into ammonia, and may even escape from the system. The ammonia-sensitive electrode method utilizes the property of ammonia escaping under strong alkaline conditions for detection.
When testing for ammonia nitrogen, bromothymol blue is added; if the color is orange, the solution is acidic, and sodium hydroxide is used to adjust it – a blue color indicates alkalinity. Hydrochloric acid is used for adjustment in order to achieve a neutral pH, ensuring that it is between 7 and 8. However, the higher the ammonia nitrogen level, it is not necessarily true that the pH will be higher
If pure ammonium salts are present, the pH will not be like this; in the case of ammonium carbonate solution, the pH is generally around 7-8