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Chromate anions (CrO 2− 4) and dichromate (Cr 2 O 7 2−) anions are the principal ions at this oxidation state. They exist at an equilibrium, determined by pH: 2 [CrO 4] 2− + 2 H + ⇌ [Cr 2 O 7] 2− + H 2 O. Chromium(VI) oxyhalides are known also and include chromyl fluoride (CrO 2 F 2) and chromyl chloride (CrO
The hydrogen chromate ion, HCrO 4 −, is a weak acid: HCrO − 4 ⇌ CrO 2− 4 + H +; pK a ≈ 5.9. It is also in equilibrium with the dichromate ion: 2 HCrO − 4 ⇌ Cr 2 O 2− 7 + H 2 O. This equilibrium does not involve a change in hydrogen ion concentration, which would predict that the equilibrium is independent of pH.
Barium chromate has been found to be useful in many capacities. The compound is often used as a carrier for the chromium ions. One such case is the use of barium chromate as a sulfate scavenger in chromium electroplating baths. [5] Over time the chromium concentration of the bath will decrease until the bath is no longer functional.
The structure of nickel chromate is the same as for chromium vanadate, CrVO 4. Crystals have an orthorhombic structure with unit cell sizes a = 5.482 Å, b = 8.237 Å, c = 6.147 Å. The cell volume is 277.6 Å 3 with four formula per unit cell. [5] [7] Nickel chromate is dark in colour, unlike most other chromates which are yellow. [3]
Lead(II) chromate can be produced by treating sodium chromate with lead salts such as lead(II) nitrate or by combining lead(II) oxide with chromic acid.. Related lead sulfochromate pigments are produced by the replacement of some chromate by sulfate, resulting in a mixed lead-chromate-sulfate compositions Pb(CrO 4) 1−x (SO 4) x.
Basic chromium sulfate is produced from chromate salts by reduction with sulfur dioxide, although other methods exist. [4] [5] The reduction could formally be written: Na 2 Cr 2 O 7 + 3 SO 2 + H 2 O → Cr 2 (SO 4) 3 + 2 NaOH. Since 33% of the anion charges are due to hydroxy ions the basicity is 33% (but in tanning jargon it is known as 33%
A chromate ester is a chemical structure that contains a chromium atom (symbol Cr) in a +6 oxidation state that is connected via an oxygen (O) linkage to a carbon (C) atom. The Cr itself is in its chromate form, with several oxygens attached, and the Cr–O–C attachment makes this chemical group structurally similar to other ester functional groups.
It may be formed by the salt metathesis reaction of potassium chromate and iron(III) nitrate, which gives potassium nitrate as byproduct. 2 Fe(NO 3) 3 + 3 K 2 CrO 4 → Fe 2 (CrO 4)3 + 6 KNO 3. It also can be formed by the oxidation by air of iron and chromium oxides in a basic environment: 4 Fe 2 O 3 + 6 Cr 2 O 3 + 9 O 2 → 4 Fe 2 (CrO 4) 3