Anionic Tests and Observations in Chemistry
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Questions and Answers

What observation occurs when a salt containing carbonate ions is treated with dilute HCl?

  • Formation of a precipitate
  • Color change to blue
  • Effervescence and CO2 evolution (correct)
  • Release of a brown gas

Which gas evolves during the experiment with SO3-2 that causes the solution to turn yellow due to precipitation of sulphide?

  • H2S
  • NO2
  • Cl2
  • SO2 (correct)

Which observation is characteristic of an acidic radical containing sulphide?

  • Clear solution with no gas evolved
  • Dense white fumes with ammonium hydroxide
  • Brown fumes evolution
  • Suffocating odour and blackness on lead acetate paper (correct)

When testing for nitrate ions (NO3-), which observation indicates their presence?

<p>Faint blue color in the solution (D)</p> Signup and view all the answers

What conclusion can be drawn if no gas is evolved when a salt is treated with concentrated H2SO4?

<p>The acidic radical may be from group II or III (C)</p> Signup and view all the answers

Which anionic test produces a white precipitate with barium chloride and is soluble in mineral acids?

<p>Borate ion (A)</p> Signup and view all the answers

What color does the solution become when testing for bromide ions with concentrated H2SO4?

<p>Reddish-brown (A)</p> Signup and view all the answers

Which compound forms when iodide ions react with concentrated H2SO4 and produces violet vapours?

<p>Iodine (I2) (B)</p> Signup and view all the answers

When identifying chloride ions, which indicates the presence of HCl gas?

<p>White clouds of ammonium chloride (C)</p> Signup and view all the answers

What is produced when nitrate ions are treated with concentrated H2SO4 and copper turnings are added?

<p>Blue color solution (C)</p> Signup and view all the answers

Which test would confirm the presence of the bromide ion using silver nitrate?

<p>Pale yellow precipitate (D)</p> Signup and view all the answers

Which of the following ions can form a white precipitate with lead acetate that is soluble in boiling water?

<p>Bromide ion (D)</p> Signup and view all the answers

Which test involves observing the disappearance of pink color upon the addition of glycerol to verify a specific anion?

<p>Borate ion (D)</p> Signup and view all the answers

What color change indicates the presence of nitrate ions in a reaction?

<p>Solution turns faint blue (A)</p> Signup and view all the answers

When testing for sulfate ions, what indicates a positive result?

<p>Solubility in mineral acids (D)</p> Signup and view all the answers

What is the expected precipitate when testing for barium ions using ammonium carbonate?

<p>Barium carbonate (A)</p> Signup and view all the answers

Which of the following tests confirms the presence of phosphate ions?

<p>Canary yellow precipitate with ammonium molybdate (D)</p> Signup and view all the answers

Which of the following confirms the presence of strontium ions through a precipitate?

<p>Strontium carbonate (D)</p> Signup and view all the answers

In a flame test, what color does calcium ions produce?

<p>Brick-red (A)</p> Signup and view all the answers

What is the significance of using copper turnings in copper nitrate tests?

<p>To evolve brown fumes (C)</p> Signup and view all the answers

What is the result of adding ammonium oxalate to a solution containing calcium ions?

<p>White ppt of calcium oxalate (D)</p> Signup and view all the answers

With respect to barium phosphate, which statement is true?

<p>It forms a white precipitate with BaCl2 (C)</p> Signup and view all the answers

What color and type of gas indicates the presence of iodide ions in a reaction?

<p>Violet vapors produced (C)</p> Signup and view all the answers

Which compound is formed when testing for potassium ions with sodium cobalt nitrite?

<p>Yellow ppt of Potassium cobalt nitrite (C)</p> Signup and view all the answers

What does a white precipitate of Ag2SO4 signify in a confirmatory test for sulfate?

<p>Presence of sulfates (B)</p> Signup and view all the answers

What gas is evolved when testing for ammonium ions using sodium hydroxide?

<p>Ammonia (A)</p> Signup and view all the answers

What color does the flame turn when testing for potassium ions?

<p>Violet (C)</p> Signup and view all the answers

Which ion is suspected if there are no gases evolved from group II upon testing?

<p>Phosphate ions (PO4-3) (D)</p> Signup and view all the answers

How can one confirm the presence of strontium ions after filtering the precipitate?

<p>By dissolving the precipitate in hydrochloric acid (B)</p> Signup and view all the answers

What is produced when sodium hydroxide is added to a magnesium salt solution?

<p>White precipitate of Mg(OH)2 (B)</p> Signup and view all the answers

Which ion would produce a pale green precipitate when treated with ammonium hydroxide?

<p>Chromic ion (Cr3+) (C)</p> Signup and view all the answers

What is the result of adding ammonium sulfide to a solution of aluminum nitrate?

<p>Formation of gelatinous white precipitate (D)</p> Signup and view all the answers

Which reagent is used in testing for ferrous ions to yield a pale blue precipitate?

<p>Potassium ferrocyanide (D)</p> Signup and view all the answers

Which of the following ions gives a brown precipitate upon reaction with ferric chloride?

<p>Fe3+ (D)</p> Signup and view all the answers

When sodium doxide reacts with chromic ion, which solution results?

<p>Yellow solution (A)</p> Signup and view all the answers

What type of precipitate is formed when lead cation is tested with dilute hydrochloric acid?

<p>White precipitate of lead chloride (A)</p> Signup and view all the answers

Which of the following solutions produces a yellow precipitate when tested with potassium iodide for mercurous cation?

<p>Solution of mercurous nitrate (C)</p> Signup and view all the answers

Which of the following best describes the precipitation of aluminum ions in the presence of ammonium hydroxide?

<p>The formation of a white gelatinous precipitate (B)</p> Signup and view all the answers

Which of the following ions would not form a precipitate with sodium hydroxide?

<p>Na+ (D)</p> Signup and view all the answers

The precipitation of which cation is confirmed by a scarlet red precipitate when combined with potassium chromate?

<p>Silver cation (D)</p> Signup and view all the answers

Which characteristic indicates the presence of cations in group II when using H2S?

<p>Precipitation as sulfides in acidic medium (C)</p> Signup and view all the answers

What is the outcome of adding dilute hydrochloric acid to a solution containing silver nitrate?

<p>Formation of a white precipitate (C)</p> Signup and view all the answers

Which of the following describes the confirmatory test result for lead cation using potassium chromate?

<p>Yellow precipitate of PbCrO4 (C)</p> Signup and view all the answers

What happens to the white precipitate formed from mercurous cation when ammonia is added?

<p>It becomes black (A)</p> Signup and view all the answers

Which of the following is the group reagent used to precipitate Group I cations?

<p>Dilute hydrochloric acid (A)</p> Signup and view all the answers

Flashcards

Identifying Carbonate (CO3-2) or Bicarbonate (HCO3-)

Effervescence (fizzing) with dilute acid (HCl), resulting in CO2 gas, which turns limewater cloudy; indicates the presence of carbonate or bicarbonate ions.

Identifying Sulfate (SO3-2)

Warming the salt with dilute acid produces SO2 gas, which turns acidified potassium dichromate paper green, and the solution remains clear.

Identifying Thiosulfate (S2O3-2)

Warming with dilute acid produces SO2 gas with a suffocating odor, turning acidified potassium dichromate paper green and turning solution yellow due to a sulfide precipitate.

Identifying Sulfide (S-2)

Warming the salt with dilute acid generates H2S gas (rotten egg smell) and blackened lead acetate paper.

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Identifying Nitrate (NO3-)

Warming the salt with dilute acid produces NO2 gas (brown fumes) with the solution becoming faint blue color.

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Sulphate (SO42-) Test

A test to confirm the presence of sulphate ions in a solution.

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Sulphate (SO42-) Confirmatory Test

Further test to verify the sulphate ion presence after BaCl2 precipitation.

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Phosphate (PO43-) Test

A test to confirm the presence of phosphate ions in a solution.

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Phosphate (PO43-) Confirmatory Test

Further tests to confirm the phosphate ion presence after BaCl2 precipitation.

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Group III Acidic Radicals

A group of acidic radicals including sulphate, phosphate, and metaborate (B4O72-).

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Bromide (Br-) Identification

A reddish-brown colour or gas forms on reaction testing.

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Iodide (I-) Identification

Forms a violet vapor or precipitates on reaction testing.

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Nitrate (NO3-) Identification

Produces brown fumes that turn dense on heat.

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Borate Ion Test

A white precipitate forms when barium chloride is added to a solution containing borate ions. This precipitate dissolves in mineral acids.

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Confirmatory Borate Test

A white precipitate of silver borate forms when silver nitrate is added to a borate solution.

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Chloride Ion Test

When concentrated sulfuric acid is added to a chloride salt, hydrogen chloride gas is evolved, forming white ammonium chloride fumes when exposed to ammonia.

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Confirmatory Chloride Test

A white precipitate of silver chloride forms when silver nitrate is added to a chloride solution. This precipitate dissolves in dilute ammonia.

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Bromide Ion Test

A reddish-brown vapor of bromine and hydrogen bromide is released when concentrated sulfuric acid is added to a bromide salt, turning the solution reddish-brown.

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Confirmatory Bromide Test

A pale yellow precipitate of silver bromide forms in the presence of silver nitrate, insoluble in dilute nitric acid.

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Iodide Ion Test

Violet iodine vapors are released when concentrated sulfuric acid is added to an iodide salt, turning starch paper blue.

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Confirmatory Iodide Test

A yellow precipitate of silver iodide forms with silver nitrate, insoluble in ammonia. A scarlet red precipitate of mercuric iodide forms when reacting with mercuric chloride.

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Barium Ion Test

A white precipitate of barium carbonate (BaCO3) forms when ammonium chloride (NH4Cl), ammonium hydroxide (NH4OH), and ammonium carbonate (NH4)2CO3 are added to a solution containing barium ions (Ba2+).

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Confirmatory Test for Barium

A yellow precipitate of barium chromate (BaCrO4) forms when potassium chromate (K2CrO4) is added to a solution containing barium ions (Ba2+). This precipitate dissolves in mineral acids.

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Flame Test for Barium

Barium ions color the flame yellowish green.

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Strontium Ion Test

A white precipitate of strontium carbonate (SrCO3) forms when ammonium chloride (NH4Cl), ammonium hydroxide (NH4OH), and ammonium carbonate (NH4)2CO3 are added to a solution containing strontium ions (Sr2+).

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Confirmatory Test for Strontium

A white precipitate of strontium oxalate (SrC2O4) forms when ammonium oxalate is added to a solution containing strontium ions.

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Flame Test for Strontium

Strontium ions color the flame crimson.

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Calcium Ion Test

A white precipitate of calcium carbonate (CaCO3) forms when ammonium chloride (NH4Cl), ammonium hydroxide (NH4OH), and ammonium carbonate (NH4)2CO3 are added to a solution containing calcium ions (Ca2+).

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Confirmatory Test for Calcium

A white precipitate of calcium oxalate (CaC2O4) forms when ammonium oxalate is added to a solution containing calcium ions.

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Magnesium Ion Test

To identify Mg2+, add NH4Cl and NH4OH to a salt solution, followed by disodium hydrogen phosphate (Na2HPO4). A white precipitate of magnesium ammonium phosphate [Mg(NH4)PO4] forms if Mg2+ is present.

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Alternative Magnesium Test

An alternative test for Mg2+ involves adding NaOH to a salt solution. A white precipitate of magnesium hydroxide [Mg(OH)2] indicates the presence of Mg2+.

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Chromic Ion Test

To confirm the presence of Cr3+, add a buffer solution (NH4Cl + NH4OH) to a chromic nitrate solution. A pale green precipitate of Cr(OH)3 forms.

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Chromic Ion Further Test

Adding sodium peroxide (Na2O2) to the chromic solution turns it yellow, indicating the formation of chromate ions (CrO4)2-. Adding NaOH to this yellow solution will again produce a pale green precipitate of Cr(OH)3.

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Aluminium Ion Test

To test for Al3+, add a buffer solution to an aluminium nitrate solution. A gelatinous white precipitate of Al(OH)3 will form.

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Ferrous Ion Test

To test for Fe2+, add a buffer solution to a ferrous ammonium sulphate solution. A green precipitate of Fe(OH)2 forms.

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Ferric Ion Test

To confirm the presence of Fe3+, add a buffer solution to a ferric chloride solution. A brown precipitate of Fe(OH)3 forms.

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Group I Cations

These cations (Pb²⁺, Ag⁺, Hg₂²⁺) are precipitated as chlorides by the addition of dilute hydrochloric acid (HCl).

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Lead Ion (Pb²⁺)

Lead(II) ions form a white precipitate of lead chloride (PbCl₂) when reacted with dilute HCl. This precipitate is soluble in hot water.

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Mercurous Ion (Hg₂²⁺)

Mercurous ions form a white precipitate of mercurous chloride (Hg₂Cl₂) when reacted with dilute HCl. This precipitate is insoluble in hot water and turns black when ammonia is added due to the formation of amino-mercuric chloride and metallic mercury.

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Silver Ion (Ag⁺)

Silver ions form a white precipitate of silver chloride (AgCl) when reacted with dilute HCl.

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Confirmatory Tests

These are additional tests used to confirm the presence of a specific cation after its initial precipitation. They often involve the formation of a colored precipitate or a solution of a specific color.

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Group II Cations

These cations are precipitated as sulfides by the addition of hydrogen sulfide (H₂S) in an acidic medium (dilute HCl).

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Solubility Product Constant (Ksp)

This constant represents the equilibrium constant for the dissolution of a sparingly soluble salt. A lower Ksp value indicates a less soluble salt, which means it will precipitate more readily.

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Common Ion Effect

Adding a common ion (an ion already present in the solution) to a saturated solution of a sparingly soluble salt will decrease the solubility of that salt.

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Study Notes

Acidic Radicals

  • Experiment: Salt + dilute HCl
  • Observation 1: Effervescence on cold, CO2 gas evolved, which renders lime water turbid.
  • Result 1: CO32- or HCO3-
  • Observation 2: SO2 gas with suffocating odor on warming, turns acidified potassium dichromate paper to green, and solution is clear.
  • Result 2: SO32-
  • Observation 3: SO2 gas with suffocating odor on warming, turns acidified potassium dichromate paper green, and solution becomes yellow due to a precipitate.
  • Result 3: S2O32- (S + SO32-)
  • Observation 4: H2S gas evolves on warming, with a rotten egg odor, and blackens lead acetate paper.
  • Result 4: S2-
  • Observation 5: NO2 gas evolves with brown fumes, and solution turns faint blue.
  • Result 5: NO3-
  • Observation 6: No gas evolved.
  • Result 6: Acidic radical is not from group I; it may be from group II or group III.

Acidic Radicals (More Detailed Scheme)

  • Experiment: Salt + concentrated H2SO4
  • Observation 1: HCl - colorless gas evolves, forming dense white fumes when a rod dipped in ammonium hydroxide is brought near the test tube.
  • Result 1: Chloride (Cl-)
  • Observation 2: HBr/Br2 - reddish brown gases, solution turns reddish brown.
  • Result 2: Bromide (Br-)
  • Observation 3: HF/I2 - violet vapors, turning starch paper blue, layer of violet sublimate, with sulfur ppt on sides of tube.
  • Result 3: Iodide (I-)
  • Observation 4: NO2 - brown fumes, which become dense, reaction mixture heated with copper turnings, solution turns faint blue.
  • Result 4: Nitrate (NO3-)
  • Observation 5: No gas evolved.
  • Result 5: Acidic radical is not from group II, it may be from group III.

Acidic Radicals (Salt solution + BaCl2 solution)

  • Experiment: Salt solution + BaCl2 solution
  • Observation 1: White ppt of insoluble in mineral acids (barium sulfate).
  • Result 1: SO42-
  • Observation 2: White ppt of soluble in mineral acids (barium phosphate or barium metaborate).
  • Result 2: PO43- or B4O72-

Acidic Radicals (Group III, SO42-, PO43-, B4O72-)

  • Sulfate ion test: Salt solution + barium chlorides, white ppt of barium sulfate, insoluble in mineral acids.
  • Phosphate ion test: Salt solution + barium chlorides, white ppt of barium phosphate, soluble in mineral acids.
  • Borate ion test: Salt solution + barium chlorides, white ppt of barium metaborate, soluble in mineral acids.

Acidic Radicals (More Tests)

  • Chloride: Salt solution + AgNO3 = white ppt (AgCl), soluble in dilute ammonia.
  • Bromide: Salt solution + AgNO3 = pale yellow ppt (AgBr), soluble in dilute nitric acid.
  • Iodide: Salt solution + AgNO3= yellow ppt (AgI), soluble in ammonia solution.
  • Nitrate: Salt solution + NaOH + warming = brown fumes NO2, solution turns pale blue.

Acidic Radicals (Group I—CO32-, HCO3-, S2-, SO32-, S2O32-, NO3-)

  • Carbonate/Bicarbonate: Effervescence with HCl, gas turns lime water milky. (CaCO3).
  • Sulfide: H2S gas with rotten egg smell, blackens lead acetate.
  • Sulfite: SO2 gas with suffocating odor, turns acidified potassium dichromate paper green.
  • Thiosulfate: SO2 gas, turning acidified potassium dichromate paper green, and solution becomes yellow due to precipitate.
  • Nitrate: NO2 gas evolves with brown fumes, solution turns faint blue.

Acidic Radicals (Group II, Cl, Br, I, NO3)

  • Chloride: Solid + few drops concentrated H2SO4 and warm (HCl gas evolves)

Basic Radicals (Group V)

  • Barium Ion (Ba2+): Salt solution + potassium chromate (K2CrO4) = yellow ppt (BaCrO4), dissolving in mineral acids. Salt solution + ammonium oxalate= white ppt (BaC2O4). Flame test: yellowish-green.

Basic Radicals (Group VI)

  • Ammonium Ion (NH4+): Salt solution + sodium hydroxide = ammonia gas (NH3) evolves-test with HCl—turns white fumes.
  • Potassium Ion (K+): Salt solution = sodium cobalt nitrite = yellow ppt (K3[Co(NO2)6]). Flame Test= violet color.

Basic Radicals (Group IV)

  • Manganese Ion (Mn2+): Salt solution + NaOH = white ppt Mn(OH)2. Salt solution + disodium hydrogen phosphate = white ppt MnHPO4.
  • Nickel Ion (Ni2+): Salt solution + NaOH = green ppt Ni(OH)2. Salt solution + NH4OH + dimethylglyoxime = red ppt Ni(DMG)2.
  • Cobalt Ion (Co2+): Salt solution + NaOH = blue ppt (Co(OH)2), changes to pink when warmed with excess NaOH.
  • Zinc Ion (Zn2+): Salt solution + NaOH = white ppt Zn(OH)2. Salt solution + potassium ferrocyanide K4[Fe(CN)6] = white ppt Zn2 [Fe(CN)6].

Basic Radicals (Group III)

  • Chromium Ion (Cr3+): Solution of chromic nitrate + buffer = pale green ppt Cr(OH)3
  • Aluminium Ion (Al3+): Solution of aluminum nitrate + buffer = gelatinous white ppt Al(OH)3
  • Ferrous Ion (Fe2+): Solution of ferrous ammonium sulfate + buffer = pale green ppt. + K4[Fe(CN)6] = pale blue ppt
  • Ferric Ion (Fe3+): Solution of ferric chloride + buffer = brown ppt Fe(OH)3 . + K4[Fe(CN)6] = dark blue ppt.

Basic Radicals (Group II—Pb, Hg2, Ag)

  • Lead Ion (Pb2+): Lead nitrate + dilute HCl = white ppt (PbCl2). Dissolves in hot water.
  • Mercurous Ion (Hg2+): Mercurous nitrate + dilute HCl = white ppt (Hg2Cl2). Becomes black in ammonia.
  • Silver Ion (Ag+): Silver nitrate + dilute HCl = white ppt (AgCl). + KI = yellow ppt (AgI). + K2CrO4 = scarlet red ppt (Ag2CrO4), soluble in nitric acid.

Group II, Subgroup A, B and Tests

  • Mercury (II): Mercuric Chloride + Hydrogen Sulphide, black precipitate.
  • Bismuth: Bismuth Nitrate + Hydrochloric Acid + Hydrogen Sulphside = Brown precipitate.
  • Cadmium: Cadmium Sulfate + Hydrochloric Acid + Hydrogen Sulphside = Yellow precipitate.
  • Copper: Copper Sulphate + Hydrochloric Acid + Hydrogen Sulphside = Black precipitate

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Description

This quiz covers various anionic tests and observations in chemistry, focusing on the reactions of different ions with acids and reagents. You will explore gaseous products, color changes, and precipitation reactions, as well as indicators for the presence of specific anions like nitrate, bromide, and chloride. Test your knowledge on these fundamental concepts in analytical chemistry!

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