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Questions and Answers
Which group of anions does Carbonate belong to?
What is the product formed when Carbonate reacts with dilute HCl?
Which metal cations are soluable in Carbonate and Bicarbonate salts?
What type of reaction occurs when Carbonate is mixed with dilute H₂SO₄?
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What can be observed as a positive result during qualitative chemical tests for anions?
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In qualitative chemical tests, what does the term 'ppt' stand for?
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Which of the following is a disadvantage of qualitative analysis?
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What indicates the presence of CO₂ during the test for carbonates?
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What is the primary reason the purple color disappears upon boiling in the reaction with $FeCl_3$?
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Which ion is insoluble in dilute HCl due to the strength of its parent acid?
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What is the effect of adding $KCN$ to $S_2O_3^{2-}$?
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What happens to solid sulfates when mixed with dilute HCl in a dry reaction?
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What is produced when silver nitrate reacts with carbonate in a salt solution?
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Which of the following reactions produces a white precipitate?
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What color is the solution when $SO_2$ is bubbled through lime water?
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Which of the following statements is true regarding bicarbonates in water?
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What is the effect of boiling on barium bicarbonate?
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Which property indicates that $SO_2$ is a reducing agent?
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What is produced alongside $SO_2$ when thiosulfate decomposes?
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What is the final product when thiosulfate reacts with dilute HCl?
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How can one differentiate between carbonate and bicarbonate in a mixture?
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Which of the following ions forms black precipitate upon reaction with silver nitrate?
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What is the parent acid of sulfide ions ($S^{2-}$)?
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What color change occurs when $Ag_2S_2O_3$ is left standing?
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Which of the following is a characteristic of hydrogen sulfide gas ($H_2S$)?
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What is the nature of thiosulfuric acid under standard conditions?
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What happens when sodium carbonate reacts with magnesium sulfate?
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Which of the following ions does NOT form soluble thiosulfate salts?
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Which reaction between thiosulfate and an acid produces gas?
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Study Notes
Anions
- Anions are classified into five groups based on their parent acid: Carbonate, Sulfur, Halide, Phosphate, and Nitrogen.
Qualitative Analysis
- Qualitative analysis involves identifying and detecting substances, both individually and in mixtures.
- The primary focus here is analyzing inorganic salts.
Formation of Salts
- Salts are formed through the reaction of an acid and a base, producing a salt and water.
- Example: HCl (acid) + NaOH (base) → NaCl (salt) + H₂O (water)
Qualitative Chemical Tests
- These tests provide quick, simple, and inexpensive methods for detecting substances.
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Advantages:
- Visually identifiable outcomes, such as color changes or precipitate formation.
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Disadvantages:
- Limited sensitivity, not suitable for low sample concentrations.
- Lack of selectivity, multiple substances can yield the same positive result, leading to potential interferences.
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Applications:
- Water analysis: Assessing the presence or absence of specific salts.
- Pharmaceuticals: Identifying active ingredients (like iron, calcium, sodium) and detecting metallic impurities from the synthesis process.
- Forensic analysis: Detecting toxic salts in samples like stomach contents.
Anion Reactions
- Dry reactions: Performed in a dry test tube, involving the interaction of a solid powder with an acid.
- Wet reactions: Reactions occur in solution, combining a salt solution with a reagent, leading to the formation of precipitates or color changes.
- Special tests: Employ specific reagents targeting one or two anions, yielding unique outcomes.
Carbonate (CO32−CO_3^{2-}CO32−)
- Parent Acid: Carbonic acid (H2CO3H_2CO_3H2CO3), a weak and unstable acid.
- Solubility: Most carbonates are insoluble in water, except those containing sodium, potassium, and ammonium ions.
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Dry reaction: Solid carbonate + dilute HCl → vigorous effervescence and evolution of CO₂ gas, confirming the presence of carbonate.
- CO₂ can be identified by:
- Being colorless and odorless.
- Causing turbidity in lime water (Ca(OH)₂).
- CO₂ can be identified by:
- Dry reaction: Solid carbonate + dilute H2SO4H_2SO_4H2SO4 → vigorous effervescence and evolution of CO₂ gas, along with the formation of a white precipitate (BaSO₄ or PbSO₄).
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Wet reaction:
- Salt solution + AgNO3AgNO_3AgNO3 → Formation of a white precipitate, Ag2CO3Ag_2CO_3Ag2CO3.
- Ag2CO3Ag_2CO_3Ag2CO3 is soluble in:
- Nitric acid: Reacts to form Ag+Ag^+Ag+, CO32−CO_3^{2-}CO32−, and water.
- Ammonia: Reacts to form a complex ion, [Ag(NH3)2]+[Ag(NH_3)_2]^+[Ag(NH3)2]+, and CO32−CO_3^{2-}CO32−.
- Boiling the solution leads to the decomposition of Ag2CO3Ag_2CO_3Ag2CO3, resulting in a white precipitate that subsequently turns yellowish-brown, Ag2OAg_2OAg2O.
- Salt solution + BaCl2BaCl_2BaCl2 or MgSO4MgSO_4MgSO4 → Formation of a white precipitate, BaCO3BaCO_3BaCO3 or MgCO3MgCO_3MgCO3.
Bicarbonate (HCO3−HCO_3^-HCO3−)
- Parent Acid: Carbonic acid (H2CO3H_2CO_3H2CO3).
- Solubility: Bicarbonates are generally soluble in water.
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Wet reaction:
- At room temperature, no precipitate forms due to the high solubility of bicarbonates.
- Salt solution + BaCl2BaCl_2BaCl2 → Formation of Ba(HCO3)2Ba(HCO_3)_2Ba(HCO3)2.
- Boiling the solution leads to the formation of BaCO3BaCO_3BaCO3 as a white precipitate, along with CO₂ and water.
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Differentiating and Separating CO32−CO_3^{2-}CO32− and HCO3−HCO_3^-HCO3− in a Mixture:
- Bicarbonates can be converted to carbonates through boiling or by adding ammonia.
- Boiling: Ba(HCO3)2Ba(HCO_3)_2Ba(HCO3)2 decomposes into BaCO3BaCO_3BaCO3, CO₂, and water.
- Adding ammonia: Ba(HCO3)2Ba(HCO_3)_2Ba(HCO3)2 reacts with NH₃ to form BaCO3BaCO_3BaCO3 and (NH4)2CO3(NH_4)_2CO_3(NH4)2CO3.
Sulfide (S2−S^{2-}S2−)
- Parent Acid: Hydrogen sulfide (H2SH_2SH2S), a very weak acid with a distinct rotten egg odor (toxic).
- Solubility: Most sulfides are insoluble in water, except those containing sodium, potassium, ammonium, barium, calcium, and strontium ions.
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Dry reaction:
- Solid sulfide + dilute HCl → Evolution of H2SH_2SH2S gas.
- H2SH_2SH2S gas can be identified by its:
- Colorless nature.
- Rotten egg odor (toxic).
- Blackening of lead acetate paper due to the formation of PbS.
- Turning cadmium acetate paper yellow due to the formation of CdS.
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Wet reaction:
- Salt solution + BaCl2BaCl_2BaCl2 → No visible reaction.
- Salt solution + AgNO3AgNO_3AgNO3 → Formation of a black precipitate, Ag2SAg_2SAg2S.
- Ag2SAg_2SAg2S is soluble in hot dilute HNO3HNO_3HNO3.
- Ag2SAg_2SAg2S is insoluble in NH3NH_3NH3.
- Salt solution + FeCl3FeCl_3FeCl3 → Formation of a black precipitate, Fe2S3Fe_2S_3Fe2S3.
Sulfite (SO32−SO_3^{2-}SO32−)
- Parent Acid: Sulfurous acid (H2SO3H_2SO_3H2SO3), a weak and unstable acid.
- Solubility: Most sulfites are insoluble in water, except those containing sodium, potassium, and ammonium ions.
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Dry reaction:
- Solid sulfite + dilute HCl → Evolution of SO2SO_2SO2 gas.
- SO2SO_2SO2 gas can be characterized by:
- Colorless nature.
- Burnt sulfur odor.
- Turbidity of lime water due to the formation of CaSO3CaSO_3CaSO3 precipitate.
- Ca(OH)2Ca(OH)_2Ca(OH)2 and SO2SO_2SO2 react to produce CaSO3CaSO_3CaSO3 and water.
- CaSO3CaSO_3CaSO3 further reacts with SO2SO_2SO2 and water to produce Ca(HSO3)2Ca(HSO_3)_2Ca(HSO3)2.
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Wet reaction:
- Salt solution + BaCl2BaCl_2BaCl2 → Formation of a white precipitate, BaSO3BaSO_3BaSO3, which dissolves in dilute HCl.
- Salt solution + AgNO3AgNO_3AgNO3 → Formation of a white precipitate, Ag2SO3Ag_2SO_3Ag2SO3, which dissolves in HNO3HNO_3HNO3 and NH3NH_3NH3 (due to complex formation).
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Wet reaction:
- Salt solution + FeCl3FeCl_3FeCl3 → Formation of a dark red color, Fe2(SO3)3Fe_2(SO_3)_3Fe2(SO3)3.
Thiosulfate (S2O32−S_2O_3^{2-}S2O32−)
- Parent Acid: Thiosulfuric acid (H2S2O3H_2S_2O_3H2S2O3), not stable and decomposes into SO2SO_2SO2, SSS, and water; it's not found in its free form.
- Solubility: Thiosulfates are soluble in water, except those containing lead, silver, mercury(I), and barium ions.
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Dry reaction:
- Solid thiosulfate + dilute HCl → Evolution of SO2SO_2SO2 gas and yellow colloidal sulfur.
- No immediate change occurs when cold, but warming or standing causes the solution to become turbid due to the liberated yellow colloidal sulfur with the release of SO₂ gas.
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Wet reaction:
- Salt solution + BaCl2BaCl_2BaCl2 → Formation of a white precipitate, Ba2S2O3Ba_2S_2O_3Ba2S2O3, if the solution is highly concentrated.
- Salt solution + AgNO3AgNO_3AgNO3 → Formation of a white precipitate, Ag2S2O3Ag_2S_2O_3Ag2S2O3, which changes to black Ag2SAg_2SAg2S over time.
- This color change occurs due to the formation of Ag2SAg_2SAg2S.
- Ag2S2O3Ag_2S_2O_3Ag2S2O3 is soluble in excess S2O32−S_2O_3^{2-}S2O32− due to the formation of a complex ion, [Ag(S2O3)2]3−[Ag(S_2O_3)_2]^{3-}[Ag(S2O3)2]3−.
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Wet reaction:
- Salt solution + FeCl3FeCl_3FeCl3 → Formation of a purple color, which disappears upon boiling.
- The purple color arises from the formation of the complex ferric thiosulfate, which decomposes upon boiling into tetrathionate and Fe2+Fe^{2+}Fe2+.
- Fe3+Fe^{3+}Fe3+ and S2O32−S_2O_3^{2-}S2O32− react to form [Fe(S2O3)2]−[Fe(S_2O_3)_2]^{-}[Fe(S2O3)2]−.
- Fe3+Fe^{3+}Fe3+ and S2O32−S_2O_3^{2-}S2O32− further react to form 2Fe2+2Fe^{2+}2Fe2+ and S4O62−S_4O_6^{2-}S4O62−.
- Salt solution + FeCl3FeCl_3FeCl3 → Formation of a purple color, which disappears upon boiling.
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Special tests:
- S2O32−S_2O_3^{2-}S2O32− reacts with KCN to form SCN−SCN^-SCN−.
- Fe3+Fe^{3+}Fe3+ reacts with SCN−SCN^-SCN− to form [Fe(SCN)]2+[Fe(SCN)]^{2+}[Fe(SCN)]2+, producing a blood-red color.
Sulfate (SO42−SO_4^{2-}SO42−)
- Parent Acid: Sulfuric acid (H2SO4H_2SO_4H2SO4), a colorless, oily liquid.
- Strong acid.
- Dehydrating agent (causes charring of organic compounds).
- Moderate oxidizing agent.
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Properties of sulfuric acid:
- Acid properties:
- H2SO4H_2SO_4H2SO4 is a diprotic acid, liberating two hydrogen ions.
- H2SO4H_2SO_4H2SO4 reacts with active metals, releasing H2H_2H2.
- Dehydrating properties:
- Causes charring with sugars.
- Acts as a drying agent, resulting in highly exothermic reactions.
- Oxidizing properties: During reduction, it can yield SO2SO_2SO2, S0S^{0}S0, or even H2SH_2SH2S, depending on the reducing agent.
- Acid properties:
- Solubility: Most sulfates are soluble in water, except those containing lead, mercury(I), barium, calcium, and strontium ions.
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Dry reaction:
- Solid sulfate + dilute HCl → No reaction, as sulfuric acid is a stronger acid than HCl.
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Wet reaction:
- Salt solution + BaCl2BaCl_2BaCl2 → Formation of a white precipitate, BaSO4BaSO_4BaSO4, which is insoluble in dilute HCl (due to the strong nature of sulfuric acid).
- Salt solution + AgNO3AgNO_3AgNO3 → Formation of a white precipitate, Ag2SO4Ag_2SO_4Ag2SO4, if the solution is highly concentrated.
- Salt solution + FeCl3FeCl_3FeCl3 → No reaction.
- Salt solution + Pb acetate → Formation of a white precipitate.
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Description
Explore the fascinating world of anions, their classification, and the qualitative methods used in detecting inorganic salts. This quiz covers the formation of salts through acid-base reactions and highlights the advantages and disadvantages of qualitative chemical tests. Test your knowledge on these fundamental concepts in chemistry!
