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Questions and Answers
What is the primary characteristic of the carbonate ion CO32- when treated with dilute HCl?
What is the primary characteristic of the carbonate ion CO32- when treated with dilute HCl?
What is the outcome of the BaCl2 test for bicarbonate ions?
What is the outcome of the BaCl2 test for bicarbonate ions?
Which of the following reactions indicates the identification of carbonate ions?
Which of the following reactions indicates the identification of carbonate ions?
Which anion is represented by the formula HCO3-?
Which anion is represented by the formula HCO3-?
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What happens to MgCO3 when bicarbonate is tested?
What happens to MgCO3 when bicarbonate is tested?
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Which test yields a reddish-brown precipitate indicative of carbonate ions?
Which test yields a reddish-brown precipitate indicative of carbonate ions?
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What is the first product formed during the ionization of carbonic acid?
What is the first product formed during the ionization of carbonic acid?
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Which of the following correctly describes the carbonate ion when tested with dilute HCl?
Which of the following correctly describes the carbonate ion when tested with dilute HCl?
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Study Notes
Physical and Inorganic Chemistry - Section 2 PMC (101)
- Qualitative determination of anions is the focus
- Cation is a positively charged fragment of a salt
- Anion is a negatively charged fragment of a salt
- Salts are formed from the reaction of an acid and a base, producing a salt and water
Qualitative Determination of Anions
- Identification of anions is based on various reactions
- Dry reactions involve treating salts with acids (dilute HCl, dilute H₂SO₄) to identify volatile products
- This method identifies volatile products
- Some acids, like HCl and H₂SO₄, displace carbonic acid
- Sub-categories include volatile products upon treatment with dilute acid, and gases developed upon use of concentrated sulfuric acid (H₂SO₄)
- Wet reactions involve color, precipitation, or oxidation-reduction reactions
- Specific and selective methods are used to classify different anions for precise identification
Identification of Carbonate Group (CO₃²⁻) and Bicarbonate (HCO₃⁻)
- The carbonate group includes carbonate (CO₃²⁻) and bicarbonate (HCO₃⁻)
- Carbonate and bicarbonate are salts of carbonic acid (H₂CO₃)
- Carbonate ion: CO₃²⁻
- Bicarbonate ion: HCO₃⁻
- Carbonic acid ionizes in two steps, producing bicarbonate and carbonate ions
Tests for Carbonate and Bicarbonate (Dry Reactions - Action of Dilute HCl)
-
Carbonate (CO₃²⁻): Effervescence (bubbling) due to CO₂ gas evolution, turning limewater turbid (cloudy) due to CaCO₃ precipitation
- CO₃²⁻ + 2H⁺ → CO₂ + H₂O
- CO₂ + Ca(OH)₂ → CaCO₃ + H₂O
-
Bicarbonate (HCO₃⁻): Similar reaction to carbonate, producing CO₂ gas
- HCO₃⁻ + H⁺ → CO₂ + H₂O
Tests for Carbonate and Bicarbonate (Wet Reactions)
-
Carbonate (CO₃²⁻): Immediate white ppt. of BaCO₃, soluble in dilute HCl
- Na₂CO₃ + BaCl₂ → BaCO₃ + 2NaCl
-
Bicarbonate (HCO₃⁻): White ppt. of BaCO₃ after boiling
- 2NaHCO₃ + BaCl₂ → Ba(HCO₃)₂ + 2NaCl
- Ba(HCO₃)₂ (on boiling) →BaCO₃ + CO₂ + H₂O
-
MgSO₄ test:
-
Carbonate (CO₃²⁻): Immediate white ppt of MgCO₃
- Na₂CO₃ + MgSO₄ → MgCO₃ + Na₂SO₄
-
Bicarbonate (HCO₃⁻): White ppt of MgCO₃ after boiling
- 2NaHCO₃ + MgSO₄ → Mg(HCO₃)₂ + Na₂SO₄
- Mg(HCO₃)₂ (on boiling) →MgCO₃ + CO₂ + H₂O
-
Carbonate (CO₃²⁻): Immediate white ppt of MgCO₃
-
HgCl₂ test:
-
Carbonate (CO₃²⁻): Reddish-brown ppt. of basic mercury carbonate (Hg₄O₃CO₃)
- 4Na₂CO₃ + 4HgCl₂ → Hg₄O₃CO₃ + 8NaCl + 3CO₂
- Bicarbonate (HCO₃⁻): No observation
-
Carbonate (CO₃²⁻): Reddish-brown ppt. of basic mercury carbonate (Hg₄O₃CO₃)
Summary of Tests for Carbonate and Bicarbonate
- Test 1 (dilute HCl): Effervescence indicates possible carbonate/bicarbonate.
- Test 2 (BaCl₂): White ppt for carbonate, white ppt after boiling for bicarbonate.
- Test 3 (MgSO₄): White ppt for carbonate, white ppt after boiling for bicarbonate.
- Test 4 (HgCl₂): Reddish-brown ppt for carbonate, no observation for bicarbonate.
Conclusion
- Carbonate (CO₃²⁻) is indicated by the presence of certain observations according to the tests performed.
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