Hepar sample

The hepar sample is a preliminary sample in the classic separation process of inorganic analysis . It is used to determine whether the sample to be analyzed contains sulfur in any form, for example as sulfide or sulfate.

Historical

The hepar sample was first mentioned in July 1697 by the chemist and physician Georg Ernst Stahl, who is known for his precise test instructions. He published it as follows:

“Secundum, quod verum Sulfur sit, probatur fusion ejus cum alcali in forma rubicunda, quae delisquescendo, sit nigra remanente tamen bona parte eliam cum alcali solubili & solutionem flavam probente quae si cum aceto praecipitetur. Lac Sulphuris cadit. "

“Secondly, that it is real sulfur is proven by its melt with potassium carbonate, which has a red appearance, which turns black when it becomes liquid, but a good part remains with Alcali as more soluble and presents a yellow solution Acid is precipitated as milk of sulfur falls. "

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procedure

A little sodium carbonate is melted on a magnesia rod (or a platinum wire) to form a small ball and this is wetted with the sample to be analyzed. This is held in the reducing flame of the Bunsen burner to reduce all sulfur compounds to sulfide. Then it is wetted with water and pressed onto a piece of bare silver . In connection with oxygen , silver sulfide is formed . This forms a yellow-brown to black spot that is reminiscent of the color of sulfur liver. Because of this similarity, the name Heparprobe (Greek hepar , liver) came about .

Silver sulfide is formed according to the reaction:

{\ displaystyle \ mathrm {4Ag + 2 {S ^ {\ operatorname {2-}} + 2H_ {2} O + O_ {2} \ longrightarrow 2Ag_ {2} S + 4 \ OH ^ {\ operatorname {-}} }}}

The hepar sample is a sensitive but not specific detection reaction, because selenium and tellurium also produce a positive reaction .

For further differentiation, the sample is heated with 1 molar sulfuric acid . This creates hydrogen sulfide (H ₂ S), which can be identified by its typical smell or by its ability to blacken lead acetate paper .

Slightly modified, the hepar sample is also known in mineralogy . A sample of the mineral is mixed with sodium carbonate (soda) and a little charcoal powder, moistened and melted with a reducing flame. Here too, sodium sulphide is formed in the presence of sulfur. This can be recognized by a yellow coloration of the sample and also leads to a black coloration of a bare silver sheet or a bare silver coin.

Individual evidence

↑ Observationum chymico-physicarium curiosarum, Mensis Primus Julius, sistens Experimentum Novum, verum Sulfur Arte producendi, Illustratum & Demnonstrantum, Frankfurt and Leipzig 1698.
↑ G. Jander, E. Blasius et al .: Textbook of analytical and preparative inorganic chemistry .
^ AF Holleman , E. Wiberg : Textbook of Inorganic Chemistry . 71–80. Edition. Walter de Gruyter, Berlin 1971, p. 727.

[1] Observationum chymico-physicarium curiosarum, Mensis Primus Julius, sistens Experimentum Novum, verum Sulfur Arte producendi, Illustratum & Demnonstrantum, Frankfurt and Leipzig 1698.

[2] G. Jander, E. Blasius et al .: Textbook of analytical and preparative inorganic chemistry .

[3] AF Holleman , E. Wiberg : Textbook of Inorganic Chemistry . 71–80. Edition. Walter de Gruyter, Berlin 1971, p. 727.