Nitrites and nitrates are salts of nitrous acid and nitric acid respectively, essential for the growth of plants that use nitrogen to synthesize proteins. For this reason, they are the main components of chemical soil fertilizers and, unfortunately, also among the major pollutants of groundwater. However, nitrites and nitrates are also used as preservative additives in foods (read the sheet).
Nitrates are harmless to the human body, but they can transform into the harmful nitrites in conditions like heat or acidic pH. Nitrites, in fact, can bind hemoglobin, reducing the ability to transport oxygen to tissues. The ability of nitrites to combine with protein rich amines produces carcinogenic nitrosamine as happens with nicotin, that in heat condition turns into N-nitrosonornicotine, a highly carcinogenic tobacco specific nitrosoamine.

Logo Avogadro

If you have not already done so, download Avogadro for free and watch the tutorials if necessary.

Open Avogadro and build nitric acid and nitrous acid molecules (pencil à element). On a separate page of Avogadro recalls the structure of N-nitrosonornicotine (fileàimportà fetch file by chemical name).

Answer the following questions:
• what kind of hybridisation and molecular geometry the nitric acid has? Check your response in properties (view àproperties) and with Lewis’s point structures.
• Are the hybridization and molecular geometry of nitrous acid predictable from the electron-point structure of Lewis?
• The general formula of nitrosamines is…

Are you able to recognize the N R portions in the molecule reported with Avogadro?
• In which portion of nitrosamine molecule built with Avogadro can you recognize part of the initial nitrous acid?
• Research whether this nitrosamine is formed not only by tobacco.

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