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Predominance diagram for chromate. A predominance diagram purports to show the conditions of concentration and pH where a chemical species has the highest concentration in solutions in which there are multiple acid-base equilibria. [1] The lines on a predominance diagram indicate where adjacent species have the same concentration.
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.
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.
The case of the chromate ion provides a relatively simple example. In the predominance diagram for chromate, shown at the right, pCr stands for the negative logarithm of the chromium concentration and pH stands for the negative logarithm of H + ion concentration. There are two independent equilibria. Equilibrium constants are defined as follows ...
The color of chemicals is a physical property of chemicals that in most cases comes from the excitation of electrons due to an absorption of energy performed by the chemical. The study of chemical structure by means of energy absorption and release is generally referred to as spectroscopy .
The change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of potassium chromate. At yet lower pH values, further condensation to more complex oxyanions of chromium is possible. Both the chromate and dichromate anions are strong oxidizing reagents at low pH ...
Chrome yellow or crocoite (PY34): lead chromate (PbCrO 4). Cobalt pigments. Aureolin or cobalt yellow (PY40): potassium cobaltinitrite (K 3 Co(NO 2) 6). Iron pigments. Yellow ochre (PY43): a naturally occurring clay of monohydrated ferric oxide (Fe 2 O 3 ·H 2 O). Lead pigments. Naples yellow (PY41). Lead-tin-yellow: PbSnO 4 or Pb(Sn,Si)O 3 ...
For example, menthone may be prepared by oxidation of menthol with acidified dichromate. [7] Tertiary alcohols cannot be oxidized. In an aqueous solution the color change exhibited can be used to test for distinguishing aldehydes from ketones. Aldehydes reduce dichromate from the +6 to the +3 oxidation state, changing color from orange to green ...