Silver chromate
| Silver chromate | ||
|---|---|---|
| Identifiers | ||
| CAS number | 7784-01-2  | |
| PubChem | 62666 | |
| ChemSpider | 56417  | |
| Jmol-3D images | {{#if:[Ag+].[Ag+].[O-][Cr]([O-])(=O)=O|Image 1 | |
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| Properties | ||
| Molecular formula | Ag2CrO4 | |
| Molar mass | 331.73 g/mol | |
| Appearance | brown-red powder | |
| Density | 5.625 g/cm3 | |
| Boiling point | 1,550 °C; 2,820 °F; 1,820 K | |
| Solubility | soluble in nitric acid, ammonia, alkali cyanides and chromates [1] | |
| Thermochemistry | ||
| Std enthalpy of formation ΔfH |
−712 kJ·mol−1[2] | |
| Standard molar entropy S |
217 J·mol−1·K−1[2] | |
| Specific heat capacity, C | 142 J/mol K | |
| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa) | ||
| Infobox references | ||
Silver chromate (Ag2CrO4) is a brown-red monoclinic crystal and is a chemical precursor to modern photography. It can be formed by combining silver nitrate (AgNO3) and potassium chromate (K2CrO4) or sodium chromate (Na2CrO4). This reaction has been important in neuroscience, as it is used in the "Golgi method" of staining neurons for microscopy: the silver chromate produced precipitates inside neurons and makes their morphology visible.
Preparation
Silver chromate is produced by an exchange reaction with a soluble silver salt, such as that between potassium chromate and silver nitrate.
Laboratory use
The use of the compound itself in the laboratory is rather limited, although its formation is used to indicate the endpoint in the titration of chloride with silver nitrate in the Mohr method of argentometry.
The solubility of silver chromate is slightly higher than that of silver chloride(Ksp = 1.1x10-12 or 6.5x10-5 moles / L). So, in a mixture of both ions silver chloride will be formed. Only when no chloride is left will silver chromate form and precipitate out.
Prior to the endpoint the solution has a milky lemon yellow appearance, due to the color of the chromate ion and the precipitate of silver chloride already formed. When approaching the endpoint, additions of silver nitrate lead to steadily slower disappearing red colorations. When the red brownish color remains (with grayish spots of silver chloride in it) the endpoint of titration is reached.
References
- ↑ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
- ↑ 2.0 2.1 Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 0-618-94690-X.
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