Micro-chemical test for hydrogen carbonate (bicarbonate)

Author: Christine Bläuer

back to Micro-chemical testing

More information about the necessary equipment and materials see Article Micro-chemistry.

Procedure

preliminary remark about the micro-chemical differentiation of carbonates and hydrogen carbonates

The micro-chemical differentiation of carbonates and hydrogen carbonates in practice is difficult. Therefore it is normally necessary to verify the obtained results by analyzing the salt samples with other methods like e.g. polarized light microscopy or other analytical methods.

pH value of hydrogen carbonate salts

The pH of an aqueous solution of alkali hydrogen carbonates lies at about 8. For mixed salts of alkali carbonates and hydrogen carbonates (e.g. Trona = Na3H(CO3)2.2H2O) the pH lies at about 10.

Hydrogen carbonate test using mineral acids

When adding diluted hydrochloric or nitric acid to the crystalline salt or the salt solution CO2 is released which can be observed as bubbling.

Hydrogen carbonate test using calcium chloride solution

Adding a drop of CaCl2 solution to a sample solution containing only HCO3- but no CO32- leads to no visible reaction.

Literature

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