Chemistry – Experimental techniques and chemical analysis - Identification of ions and gases | e-Consult
Experimental techniques and chemical analysis - Identification of ions and gases (1 questions)
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Test 1: Reaction with Dilute Acid
- A small amount of the unknown salt is added to dilute hydrochloric acid (HCl) or dilute sulphuric acid (H2SO4).
- The reaction is observed for effervescence (the production of bubbles).
- If carbon dioxide gas is produced, the solution will fizz. This is because the carbonate ion reacts with the acid to form carbonic acid (H2CO3), which is unstable and decomposes into carbon dioxide and water.
- The balanced chemical equation for the reaction is: CO32-(aq) + 2H+(aq) → H2CO3(aq) → H2O(l) + CO2(g)
Test 2: Testing for Carbon Dioxide Gas
- The gas evolved in the first test is passed into limewater (calcium hydroxide solution, Ca(OH)2).
- If carbon dioxide is present, the limewater will turn milky due to the formation of calcium carbonate (CaCO3).
- The balanced chemical equation for the reaction is: CO2(g) + Ca(OH)2(aq) → CaCO3(s) + H2O(l)
Conclusion: If both tests show effervescence in the first test and the limewater turns milky in the second test, it confirms the presence of the carbonate ion.