Micro-chemical test for hydrogen carbonate (bicarbonate): Difference between revisions
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For more information on the required equipment and materials see the Micro-chemistry article. | 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. | The micro-chemical differentiation of carbonates and hydrogen carbonates, i.e., bicarbonates, 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 == | == Procedure == | ||
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An aqueous solution of alkali hydrogen carbonate has a pH of around 8. | 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 (Na<sub>3</sub>H(CO<sub>3</sub>)<sub>2</sub>.2H<sub>2</sub>O) the pH is around 10. | For mixed salts of alkali carbonates and hydrogen carbonates (e.g., trona (Na<sub>3</sub>H(CO<sub>3</sub>)<sub>2</sub>.2H<sub>2</sub>O) the pH is around 10. | ||
===Hydrogen carbonate test using mineral acids === | ===Hydrogen carbonate test using mineral acids === | ||
When adding diluted hydrochloric or nitric acid | When adding diluted (2M) hydrochloric or nitric acid to the crystalline salt or the salt solution, CO<sub>2</sub> is released and can be observed as bubbling. | ||
===Differentiation between hydrogen carbonate and carbonate using calcium chloride solution === | ===Differentiation between hydrogen carbonate and carbonate using calcium chloride solution === | ||
Adding a drop of CaCl<sub>2</sub> solution (1% aqueous solution) to a sample solution containing only HCO<sub>3</sub><sup>-</sup> | Adding a drop of CaCl<sub>2</sub> solution (1% aqueous solution) to a sample solution containing only HCO<sub>3</sub><sup>-</sup>, i.e., no CO<sub>3</sub><sup>2-</sup> present, will not produce any visible reaction. | ||
== Literature == | == Literature == | ||
Latest revision as of 22:31, 24 November 2017
Author: Christine Bläuer
back to Micro-chemical testing
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, i.e., bicarbonates, 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 (2M) hydrochloric or nitric acid to the crystalline salt or the salt 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-, i.e., no CO32- present, will not produce any visible reaction.