26Study Notes: Synthesis and Properties of Pink Salt (Ammonium Hexachloridostannate(IV))

Properties and Characteristics of Pink Salt (Ammonium Hexachloridostannate(IV))

• Name and Systematic Designation: The preparation P26 is known as "Pinksalz" or Ammoniumhexachloridostannat(IV).
• Chemical Formula: $(NH_4)_2[SnCl_6]$.
• Physical Appearance: It is a white crystalline solid.
• Density: The density of the solid is $2.39\,g/cm^3$.
• Stability and Solubility:
      * The substance is stable in air.
      * It is highly soluble in water.
      * Behavior in Dilute Solutions: Dilute solutions of the salt become cloudy when left standing in the air. This phenomenon is due to the formation of Zinn(IV)-säure (Tin(IV) acid).

Theoretical Foundations and Research Requirements

• Chemical Context: The study of this preparation involves understanding the chemistry of Tin (specifically its oxidation states in aqueous media and its complex compounds) and redox reactions.
• Synthesis Rationale:
      * Aqua Regia (Königswasser): Research is required to explain why Aqua Regia is necessary for the synthesis of this complex.
      * Etymology: Students must investigate the historical origin of the name "Pinksalz."
• Application in Dyeing (Beizenfärbung):
      * The salt is historically significant in the process of mordant dyeing.
      * The student must be able to sketch the process using structural formulas.
      * Special attention must be paid to the role of the metal ion ($Sn^{4+ shadow}$) in binding the dye to the fiber.
• Literature Reference: The procedure is based on J. Strähle, E. Schweda, Jander‐Blasius ‐ Lehrbuch der analytischen und präparativen anorganischen Chemie, S. Hirzel Verlag 16th Edition, 2006, Page 228.

Safety Protocols and Handling

• GHS Compliance: Students must be familiar with the H-statements (Hazard statements) and P-statements (Precautionary statements) for all chemicals used.
• Verbal Translation: Information should be reproducible in the student's own words rather than simply reading lists of numbers.
• Specific Hazards:
      * Nitrogen Oxides (Stickoxide): These are highly toxic. All work involving their production must be performed under a fume hood (Abzug).
      * Acid Handling: Aqua Regia and hydrochloric acid involve significant chemical hazards.

Materials and Reagents for Synthesis

• Granulated Tin (Zinn): $2.5\,g$.
• Ammonium Chloride ($NH_4Cl$): $4.5\,g$.
• Nitric Acid ($HNO_3$): Concentrated, $65\%$ (sourced from the assistant's station).
• Hydrochloric Acid ($HCl$): $24\%$ (sourced from the standard set).
• Aqua Regia (Königswasser): A total of approximately $50\,ml$ is prepared by mixing the $65\%\,HNO_3$ and $24\%\,HCl$ in a specific ratio under the fume hood.
• Distilled Water: Used for dissolving salts and washing the final product.

Detailed Synthesis Procedure

• Dissolution Phase:
      * In a $100\,ml$ beaker, $2.5\,g$ of granulated tin is combined with approximately $10\,ml$ of the prepared Aqua Regia.
      * The mixture is heated (using a burner, tripod, and Ceran plate) and boiled until the tin has completely dissolved.
      * Crucial Maintenance: If the volume of Aqua Regia decreases significantly before the tin is dissolved, more must be added. The mixture must never be allowed to evaporate to dryness (eindampfen), as this would destroy the batch.
      * Avoid Contamination: Stirring must be performed only with a glass rod. Iron spatulas must not be used because they dissolve in the acid and contaminate the product with iron ions.
• Removal of Nitric Acid ("Abrauchen"):
      * After the tin has dissolved, if brown fumes are still observed, $24\%\,HCl$ is added.
      * The solution is heated to remove excess nitric acid. The nitric acid is exclusively required for the oxidation of the tin.
      * This result is a solution containing Hexachloridozinn(IV)-säure (Hexachloridostannic(IV) acid).
• Precipitation and Recrystallization:
      * A saturated solution of ammonium chloride is prepared by dissolving $4.5\,g$ of $NH_4Cl$ in the minimum possible amount of distilled water.
      * This solution is added to the tin solution, causing a precipitate to form.
      * Add approximately $10\,ml$ of hot distilled water until the precipitate just redissolves.
      * The clear solution is then filtered through a Büchner funnel (hot filtration) to remove any remaining undissolved impurities.
• Concentrating and Crystallization:
      * The filtrate is transferred to a porcelain dish and concentrated over a water bath (using a crystallization dish as the bath) on a burner/tripod setup.
      * Heating continues until the first crystals appear on the bottom of the dish or the surface of the liquid. It must not be evaporated to dryness.
      * The dish is then placed in an ice bath for approximately $0.5\,hours$ (30 minutes) to allow the product to crystallize completely.
• Filtration and Drying:
      * The crystals are filtered via a Büchner funnel using a membrane pump vacuum.
      * The product is washed with a very small amount of ice-cold distilled water that has been acidified with a few drops of hydrochloric acid.
      * Drying Methods: The product can be air-dried under the fume hood or dried by pulling air through the Büchner funnel with the membrane pump until the substance is dry.

Laboratory Documentation and Presentation

• Lab Journal: All weighings (Einwaagen), conditions, and observations must be meticulously recorded.
• Photography: It is recommended to document experimental setups with photos.
• Final Report (Versuchsvorschrift): A written elaboration must be prepared following the provided template.
• Introductory Presentation: A short presentation is required at the scheduled time to explain the chemical background and the practical steps of the synthesis. This serves as a preliminary discussion and practice for communicating chemical facts.