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Predominance diagram for chromate. In aqueous solution, chromate and dichromate anions exist in a chemical equilibrium.. 2 CrO 2− 4 + 2 H + ⇌ Cr 2 O 2− 7 + H 2 O. The predominance diagram shows that the position of the equilibrium depends on both pH and the analytical concentration of chromium.
Using these values and the equality conditions, the concentrations of the three species, chromate CrO 2− 4, hydrogen chromate HCrO − 4 and dichromate Cr 2 O 2− 7 can be calculated, for various values of pH, by means of the equilibrium expressions. The chromium concentration is calculated as the sum of the species' concentrations in terms ...
When the pH of the solution is increased by adding an alkaline solution to it, the extent of hydrolysis increases. Measurements of pH or colour change are used to derive the equilibrium constant for the reaction. Further hydrolysis may occur, producing dimeric, trimeric or polymeric species containing hydroxy- or oxy- groups.
The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency towards further change. For a given set of reaction conditions, the equilibrium constant is ...
Chemical equilibrium Le Chatelier's principle ... Chromate and dichromate. Lead(II) chromate. Chrome yellow; ... Equilibrium constant. Dissociation constant;
The pK a for the equilibrium is not well characterized. Reported values vary between about −0.8 to 1.6. [4] The structure of the mono anion has been determined by X-ray crystallography. In this tetrahedral oxyanion, three Cr-O bond lengths are 156 pm and the Cr-OH bond is 201 pm [5] [HCrO 4] − condenses to form dichromate:
Strontium chromate is approximately 30 times more soluble in water at 100 °C than at room temperature. Therefore, the yellow strontium chromate can be suspended in a hot solution of a soluble sulfate to digest until fully converted to the much less soluble and white strontium sulfate, leaving the chromate or dichromate in solution.
Equilibrium constants are defined in terms of fugacity. If the gases are at sufficiently low pressure that they behave as ideal gases, the equilibrium constant can be defined as a quotient of partial pressures. An example of gas-phase equilibrium is provided by the Haber–Bosch process of ammonia synthesis.