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The solution needs to be near neutral, because silver hydroxide forms at high pH, while the chromate forms Ag 2 Cr 2 O 7 or AgHCrO4 at low pH, reducing the concentration of chromate ions, and delaying the formation of the precipitate. Carbonates and phosphates precipitate with silver, and need to be absent to prevent inaccurate results.
Silver chromate is an inorganic compound with formula Ag 2 CrO 4 which appears as distinctively coloured brown-red crystals. The compound is insoluble and its precipitation is indicative of the reaction between soluble chromate and silver precursor salts (commonly potassium/sodium chromate with silver nitrate).
The following chart shows the solubility of various ionic compounds in water at 1 atm pressure and room temperature (approx. 25 °C, 298.15 K). "Soluble" means the ionic compound doesn't precipitate, while "slightly soluble" and "insoluble" mean that a solid will precipitate; "slightly soluble" compounds like calcium sulfate may require heat to precipitate.
The tables below provides information on the variation of solubility of different substances (mostly inorganic compounds) in water with temperature, at one atmosphere pressure.
Silver chloride – AgCl; Silver chromate – Ag 2 CrO 4; Silver fluoroborate – AgBF 4; Silver fulminate – AgCNO; Silver hydroxide – AgOH; Silver iodide – AgI; Silver nitrate – AgNO 3; Silver nitride – Ag 3 N; Silver oxide – Ag 2 O; Silver perchlorate – AgClO 4; Silver permanganate – AgMnO 4; Silver phosphate (silver ...
Silver bromate: 4.24 Silver bromide: 12.11 Silver carbonate: 11.21 Silver chloride: 9.97 Silver chromate: 11.05 Silver cyanide (Ag[Ag(CN) 2]) 11.66 (20 °C) Silver dichromate: 6.70 Silver hydroxide: 7.82 (20 °C) Silver iodate: 8.04 (9.4 °C) Silver iodide: 15.82 Silver thiocyanate: 11.94 Strontium carbonate: 8.80 Strontium fluoride: 8.55 (18 ...
The chromate and dichromate ions are fairly strong oxidizing agents. Commonly three electrons are added to a chromium atom, reducing it to oxidation state +3. In acid solution the aquated Cr 3+ ion is produced. Cr 2 O 2− 7 + 14 H + + 6 e − → 2 Cr 3+ + 7 H 2 O ε 0 = 1.33 V. In alkaline solution chromium(III) hydroxide is produced.
Some silver oxide powder.. Silver is a relatively unreactive metal, although it can form several compounds. The common oxidation states of silver are (in order of commonness): +1 (the most stable state; for example, silver nitrate, AgNO 3); +2 (highly oxidising; for example, silver(II) fluoride, AgF 2); and even very rarely +3 (extreme oxidising; for example, potassium tetrafluoroargentate(III ...