I worked on a project at school for determining nitrogen content in water from a local lake. This is the digested lake water right off the heating block, prior to dilution. Total nitrogen content of various substances can be quantified by Kjeldahl digestion and subsequent titration. For this project, the lake water was added to a tube with sulfuric acid and copper sulfate and digested at 390° C. The copper sulfate makes it blue

Я работал над проектом в школе по определению содержания азота в воде местного озера. Это обработанная озерная вода сразу после нагревательного блока перед разбавлением. Общее содержание азота в различных веществах может быть определено с помощью разложения по методу Кьельдаля и последующего титрования. Для этого проекта вода из озера была добавлена ​​в пробирку с серной кислотой и сульфатом меди и обработана при температуре 390 ° C. Сульфат меди придает ей синий цвет.

Mohr's method for the determination of chloride was founded by and named after german chemist Karl Friedrich Mohr (1806-1878). A solution of silver nitrate is added to the flask contaning chloride ions, potassium chromate is used as an indicator. While added, a precipate of silver chloride forms (Picture 1). The end point is indicated by the red-brown precipate of silver chromate (Picture 2). In the last picture i overshot the titration to better show the color of silver chromate. The titration is carried out in solutions with a pH of 6.5-9. If the solution is to acidic, the chromate will Form dichromate which won't Form an insoluble salt. If to basic, the added silver solution will Form silver oxid or silver hydoxide.

The method can also be used to determine the amount of bromide ions. It may be a little outdated, but still works nicely.

Note: potassium chromate (K2CrO4) is toxic and carcinogen. Silver nitrate is corrosive and can seriously damage your skin etc. Always be carefull!
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