Nessler s reagent

Mcrcuryill) iodide, HgL. Scarlet (to 126 C) or yellow substance (HgC L solution plus KI or Hg plus I2)- Forms complex iodides with excess iodide (Nessler s reagent). 

Nessler s reagent An alkaline solution of Hglj in KI used for detecting and estimating ammonia (brown colour or precipitate formed). 

All ammonium salts evolve ammonia on heating with alkali. Ammonia may be delected by (a) its smell, (b) its action in turning red litmus blue and (c) the orange-brown colour produced with Nessler s reagent. This is a very sensitive test. 

Ammonia present in very small quantities in solution may be estimated by comparing the intensity of colour produced with Nessler s reagent (p. 439) with standard colours, using a simple form of colorimeter called a Nessleriser . 

Nessler s reagent (for free ammonia) dissolve 50 g of K1 in the least possible amount of cold water add a saturated solution of HgClj until a very slight excess is indicated add 400 mL of a 50% solution of KOH allow to settle, make up to a liter with water, and decant. 

The other method is less accurate but more rapid and involves direct Nessleri2ation of the sample for colorimetric deterrnination. Other colorimetric indicators with more sensitivity, such as indophenol, have been used in place of Nessler s reagent. Ion-selective electrodes have also found use in analysis for trace ammonia (93). 

Discussion. J. Nessler in 1856 first proposed an alkaline solution of mercury(II) iodide in potassium iodide as a reagent for the colorimetric determination of ammonia. Various modifications of the reagent have since been made. When Nessler s reagent is added to a dilute ammonium salt solution, the liberated ammonia reacts with the reagent fairly rapidly but not instantaneously to form an orange-brown product, which remains in colloidal solution, but flocculates on long standing. The colorimetric comparison must be made before flocculation occurs. 

The reaction with Nessler s reagent [an alkaline solution of potassium tetraiodomercurate(II)] may be represented as ... 

If necessary, dilute the sample to give an ammonia concentration of 1 mg L 1 and fill a 50 mL Nessler tube to the mark. Prepare a series of Nessler tubes containing the following volumes of standard ammonium chloride solution diluted to 50 mL 1.0,2.0,3.0,4.0,5.0, and 6.0 mL. The standards contain 0.01 mg NH3 for each mL of the standard solution. Add 1 mL of Nessler s reagent to each tube, allow to stand for 10 minutes, and compare the unknown with the standards in a Nessler stand (Section 17.4) or in a BDH Nesslerimeter. This will give an approximate figure which will enable another series of standards to be prepared and more accurate results to be obtained. 

Urea (Nitrogen) Urease, Na2W( >4, Nessler s Reagent 490... 

In caustic soda or caustic potash solution, mercury(TI) iodide forms complex salts, Na2Hgl4 and K2Hgl4, respectively. Alkaline solution of this complex in excess potassium hydroxide is known as Nessler s reagent, used to analyze ammonia. The reaction of Nessler s reagent with ammonia may be written as ... 

The compound is prepared and marketed only in aqueous solution. It is used mostly as a disinfectant and a topical antiseptic. Also, it is used to make Nessler s reagent for analyzing ammonia, and as an analytical reagent for alkaloids. 

All this can mean that, if the aq soln of unknown sample is colorless in Test 2, no ppt with,Nessler s reagent, no color with ethylene-diamine in Test 2, deep blue color with DPhA in Test 3 and green a>lor with thymol soln in Test 4, it could be NG... 

Reaction to Ammonium Ion (Nessler s Reagent). Introduce 5 ml of a 0.1 N mercury(II) nitrate solution heated to 80 °C into a 50-ml beaker and add 5 ml of a 0.1 A potassium iodide solution. Cool the mixture, let the precipitate settle, pour off the solution, and wash the precipitate three times with cold water by decantation. Add 0.2 g of potassium iodide dissolved in 5 ml of water to the precipitate. When the latter dissolves, pour in 3 ml of a 10% sodium hydroxide solution and transfer the contents into a dark jar. 

Accdg to A.R. Lusardi of picArsn, LSt does not form any ppt with Nessler s Reagent. The presence of lead can be verified by hydrogen sulfide test, potassium dichromate test or dithizone test Basic Lead Styphnate (Baste LSt)... 

To a 25 nil of condensate in a 50 ml Nessler tube was added from a pipette 5 ml of Nessler s reagent and distd w to the mark. Tbe presence of ammonia was indicated by the appearance of brown turbidity due to the formation of NHg,I - HjO and the intensity of this turbidity was detd colori-metrically using the Nalco Phototester, which was previously calibrated by using freshly prepd standards... 

Ammonium Salts. — Carefully add 2 cc. of fuming sulphuric acid, by drops, to 30 cc. of water, and add aqueous solution (1 6) of potassium hydroxide to alkalinity on now adding 10 to 15 drops of Nessler s reagent, at most a pale-yellow, but in no case a brownish-red, color or precipitate may develop. 

Ammonium Compounds. — On adding 1 cc. of Nessler s reagent to a solution of 10 gm. of sodium carbonate in 50 cc. of water, no change should be observed. 

Ammonium. Hie solution of 3 gm. of sodium chloride in 20 re. of water should not bo changed in appearance on the addition of Nessler s reagent. 

The well known Nessler s reagent for ammonia is a solution of mercuric oxide in aqueous potassium iodide. 

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