Soda extract
In qualitative analytical chemistry, soda extract is a method for separating possibly interfering cations when determining anions .
Execution and response
About four to five times the amount of crystalline sodium carbonate is added to the mixture of substances to be analyzed . After adding water, the mixture is boiled ( digested ) for about 10 minutes and then filtered off. The carbonate ions react when boiling with water to form hydrogen carbonate and hydroxide ions ( acid-base reaction ). Many cations are thus precipitated as carbonates and hydroxides .
In the filtrate, the soda extract, the anions contained in the mixture of substances to be analyzed can then be determined. It contains the sodium salts of the anions previously contained in the sample. The (heavy metal) cations that have now been converted into poorly soluble carbonates and hydroxides are in the filter residue.
Disruptions
It should be noted that undesired reactions can also take place in the solution during the digestion. The simultaneous presence of elemental zinc means , for example, that the nitrate ions originally present in the soda extract can no longer be detected because they are reduced to nitrite .
In the presence of bismuth ions, nitrate can get into the residue of the soda extract, as bismuth ions form poorly soluble basic salts with nitrate. Thus, nitrate can no longer be detected in the soda extract.
Individual evidence
- ^ Brockhaus ABC Chemie , VEB FA Brockhaus Verlag Leipzig 1965, p. 1306.