Write the net-ionic equation for the chemical reaction that occurs in each of the following qualitative tests.
The production of carbon dioxide gas in the test for carbonate.
The production of the white precipitate in the test for sulfate.
The production of the aqueous Fe(SCN) complex ion in the test for thiocyanate.
The Correct Answer and Explanation is :
Net Ionic Equations and Explanations for Qualitative Tests
- Test for Carbonate – Production of Carbon Dioxide Gas
Net Ionic Equation:
[
\text{CO}_3^{2-} (aq) + 2H^+ (aq) \rightarrow \text{CO}_2 (g) + \text{H}_2\text{O} (l)
]
Explanation:
The carbonate ion ((\text{CO}_3^{2-})) reacts with acid ((H^+)), typically from hydrochloric acid ((\text{HCl})) or nitric acid ((\text{HNO}_3)), to produce carbon dioxide gas ((\text{CO}_2)) and water. The evolution of bubbles is an indicator of the presence of carbonate ions. This reaction is widely used to identify carbonate-containing substances such as limestone ((\text{CaCO}_3)). - Test for Sulfate – Formation of White Precipitate
Net Ionic Equation:
[
\text{Ba}^{2+} (aq) + \text{SO}_4^{2-} (aq) \rightarrow \text{BaSO}_4 (s)
]
Explanation:
When barium ions ((\text{Ba}^{2+})), typically from barium chloride ((\text{BaCl}_2)), are added to a solution containing sulfate ions ((\text{SO}_4^{2-})), a white precipitate of barium sulfate ((\text{BaSO}_4)) forms. This reaction is highly specific because (\text{BaSO}_4) is an insoluble salt, making it a reliable qualitative test for sulfates. - Test for Thiocyanate – Formation of Fe(SCN) Complex
Net Ionic Equation:
[
\text{Fe}^{3+} (aq) + \text{SCN}^- (aq) \rightarrow [\text{Fe(SCN)}]^{2+} (aq)
]
Explanation:
When thiocyanate ions ((\text{SCN}^-)) react with ferric ions ((\text{Fe}^{3+})), a deep red complex ion, ([\text{Fe(SCN)}]^{2+}), is formed. This reaction is used in forensic and laboratory analysis to detect iron(III) ions. The red color intensity correlates with the concentration of ferric ions in the solution.
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Here is an illustration depicting the three qualitative chemical tests: carbonate (CO₂ gas formation), sulfate (white precipitate), and thiocyanate (red complex). Let me know if you need any modifications or further explanations!