Micro-chemical test for hydrogen carbonate (bicarbonate)

Author: Christine Bläuer

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Micro-chemical test for hydrogen carbonate (HCO₃^-)

For more information on the required equipment and materials see the Micro-chemistry article.

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

The micro-chemical differentiation of carbonates and hydrogen carbonates is difficult in practice. Therefore it is generally necessary to verify the obtained results by analyzing the salt samples with other methods, such as polarized light microscopy or other analytical procedures.

Procedure

pH value of hydrogen carbonate salts

An aqueous solution of alkali hydrogen carbonate has a pH of around 8.

For mixed salts of alkali carbonates and hydrogen carbonates (e.g., trona (Na₃H(CO₃)₂.2H₂O) the pH is around 10.

Hydrogen carbonate test using mineral acids

When adding diluted hydrochloric or nitric acid (2M) to the crystalline salt or its solution, CO₂ is released and can be observed as bubbling.

Differentiation between hydrogen carbonate and carbonate using calcium chloride solution

Adding a drop of CaCl₂ solution (1% aqueous solution) to a sample solution containing only HCO₃^- but no CO₃^2- leads to no visible reaction.