Organic QA Flashcards
What is the distinguishing test for alkanes and what’s the reaction behind it?
Test, type of reaction and equation
In dark, orange Br₂(aq) remains orange
In UV light, orange Br₂(aq) decolourises
Reaction: Free Radical substitution
Equation: RH + X₂ → RX + HX
What is the distinguishing test for alkenes and what is the reaction behind it?
Test, type of reaction and equation
- Test: Br₂ (aq) or Br₂ dissolved in CCl₄
Positive observation: Orange Br₂ decolourises
Reaction: Electrophilic addition
Equation: H₂C=CH₂ + X₂ → CH₂X-CH₂X - Test: Cold KMnO₄ (aq) in Na₂CO₃ (aq)
Positive observation: Purple KMnO₄ turns colourless and brown ppt. (MnO₂) formed
Reaction: Oxidation
Equation: H₂C=CH₂ + [O] + H₂O → (diol that looks like whiskers)
How to distinguish between terminal and non-terminal alkene?
Test, type of reaction and equation
Test: KMnO4(aq), dilute H2SO4, heat, pass gaseous product in limewater
Terminal alkene: purple KMnO4 decolourises and CO2 formed
Equation: alkene + [O] → CO2 + H2O
Non-terminal alkene: Purple KMnO4 decolourises but no CO2 formed
Reaction: Oxidation
How to distinguish between methylbenzene and other substituted benzene?
Test, type of reaction and equation
Test: H2SO4(aq), KMnO4(aq), heat
Methylbenzene (positive observation): Purple KMnO4 decolourises, when cooled, white ppt. formed (benzoic acid)
Reaction: Ar-CH3 + 3[O] → Ar-COOH + H2O
What is the distinguishing test for ethylbenzene?
Test: H2SO4, KMnO4, heat
Positive observation: Purple KMnO4 turns colourless, when cooled, white ppt. formed, CO2 evolved
Equation: Ar-CH2CH3 + 6[O] → Ar-COOH + CO2 + H2O
What is the distinguishing test for alkyl halides?
- Test: Heat with NaOH(aq) for a few minutes, acidify cooled products with HNO3 (aq), add AgNO3(aq)
Equation: RX + OH- → R-OH + X-
Ag⁺ (aq) + X⁻ (aq) → AgX (s)
Observation for both tests:
White ppt: Cl⁻
Cream ppt: Br⁻
Yellow ppt: I⁻
No ppt: Aryl halide (or just not alkyl halide)
What is the distinguishing test for alcohols?
- solid anhydrous PCl5
- SOCl2
- a few drops of enthanoyl chloride
- Warm with ethanoic acid and a few drops of conc. H2SO4, pour into water
- sodium, evaporate resultant mixture to dryness
What is the test, observation, reaction and equation of alcohol distinguishing test with solid anhydrous PCl5?
Test: Add solid anhydrous PCl5, test fumes with moist blue litmus paper and AgNO3 (one drop on end of glass rod)
Observation: White fumes observed, fumes turn moist blue litmus red and white ppt. formed with AgNO3
Reaction: Nucleophile substitution
Equation: ROH + PCl5 → RCl + HCl + POCl3
What is the test, observation, reaction and equation of alcohol distinguishing test with SOCl2?
Test: Add SOCl2, test fumes with moist blue litmus paper and AgNO3 (one drop on end of glass rod)
Observation: SO2 (can do additional tests) and white fumes produced, fumes turn moist blue litmus red and white ppt. formed with AgNO3
Reaction: Nucleophilic substitution
Equation: ROH + SOCl2 → RCl + SO2 + HCl
What is the test, observation, reaction and equation of alcohol distinguishing test with ethanoyl chloride?
Test: A few drops of ethanoyl chloride, test fumes with moist blue litmus paper and AgNO3 (one drop on end of glass rod)
Observations: White fumes produced, fumes turn moist blue litmus red and white ppt. formed with AgNO3
Reaction: nucleophilic substitution
Equation: ROH + CH3COCl → CH3COOR + HCl
What is the test, observation, reaction and equation of alcohol distinguishing test with ethanoic acid?
Test: Warm with ethanoic acid and a few drops of conc. H2SO4, pour in water
Observation: A sweet-smelling substance (ester) was formed
Equation: RCOOH + R’OH → RCOOR’ + H2O
What is the test, observation, reaction and equation of alcohol distinguishing test with sodium?
Test: Add sodium, evaporate resultant mixture to dryness
Observation: H2 produced, white crystalline solid remains
Equation: ROH + Na → RONa + 1/2H2
Reaction: Acid metal reaction
How to distinguish between primary or secondary alcohol and tertiary alcohol or phenol?
Test: warm, dilute H2SO4, KMnO4(aq)
Primary or secondary alcohol: Purple KMnO4 decolourises
Tertiary alcohol or phenol: KMnO4 remains purple
Reaction: Oxidation (tertiary alcohols and phenols are resistant to oxidation)
How to differentiate between primary, secondary and tertiary alcohols?
Lucas reagent
Test: Stir a few drops of cold ZnCl2 in conc. HCl
tertiary alcohol: white ppt. forms rapidly
secondary alcohol: white ppt. forms slowly
primary alcohol: solution remains colourless (white ppt. forms very slowly)
Reaction: nucleophilic substitution
Equation: ROH + HCl → RCl + H2O
How to differentiate alcohols and carboxylic acids since carboxylic acids also react with solid anhydrous PCl5 and SOCl2?
Alcohols: do not change moist blue litmus paper red
Carboxylic acid: turns moist blue litmus red (pH < 7)
What are the distinguishing tests for phenol?
- RCOCl, NaOH
- ferric chloride
- Br2(aq)
What is the test, observation, reaction and equation of phenol and RCOCl, NaOH?
Observation: sweet smelling substance formed (ester)
Reaction: Acid-base, Condensation
Equations:
Ar-OH + NaOH → Ar-O⁻Na⁺ + H2O
RCOCl + Ar-O⁻ → RCOOAr + Cl⁻
What is the test, observation of phenol and ferric chloride?
Test: Add one drop of neutral FeCl3
Observation: violet colouration
What is the test, observation, reaction and equation of phenol and Br2?
Test: Add Br2 (aq) gradually
Observation: Orange Br2 (aq) rapidly decolourises, white ppt. formed upon adding excess Br2 (aq)
Reaction: Electrophilic substitution
Equation: Ar-OH + 3Br₂ → 2,4,6-tribromophenol + 3HBr
What is the distinguishing test for carbonyl compounds?
Test: 2,4-DNPH
Positive test: Yellow ppt.
Reaction: Condensation reaction
Equation: (search online)
What is the distinguishing test for methyl carbonyl?
Test: Tri-iodomethane (Warm I₂ in NaOH (aq))
Positive test: Pale yellow ppt. with characteristic antiseptic smell
Equation: RCOCH3 + 3I₂ + 4OH⁻ → CHI3 + RCOO⁻ + 3H₂O
What is the distinguishing test for aliphatic aldehyde?
Test: Fehling’s reagent, warm
Positive test: brick red ppt. of Cu₂O formed
Reaction: Oxidation
Equation: RCHO + 2Cu²⁺ + 5OH⁻ → RCOO⁻ + Cu₂O + 3H₂O
What is the distinguishing test for aldehydes?
Test: Tollens’ reagent, warm
Positive test: Silver mirror formed
Equation: RCHO + 2[Ag(NH₃)₂]⁺ + 3OH⁻ → RCOO⁻ + 2Ag (s) + 4NH₃ + 2H₂O
*methanoic acid HCOOH gives false positive
How to prepare Tollens’ reagent?
NaOH(aq) is added to a solution of AgNO3 dropwise until a light brown precipitate is obtained. To this, conc. NH3 solution is added dropwise until the brown precipitate of Ag2O dissolves completely. The amount of NH3 should be sufficient enough to dissolve the precipitate completely until a clear solution is obtained.
What is tri-iodomethane test?
- how to conduct it?
- What is positive test result?
- What compounds test positive?
- what is the equation?
- What is the type of reaction?
- I₂ (aq), NaOH (aq), warm in water bath
- Pale yellow ppt. with characteristic antiseptic
- Alcohols with -CH(OH)CH3 group or carbonyl compounds with -COCH3 group
- RCH(OH)CH₃ (aq) + 4I₂ (aq) + 6OH⁻ (aq) → RCOO⁻ (aq) + CHI₃ (s) + 5I⁻ (aq) + 5H₂O (l)
- Oxidation
What are the tests to distinguish aldehyde and ketone?
- Fehling’s reagent, warm
- Tollens’ reagent, warm
- acidified K₂Cr₂O₇, heat
- acidified KMnO₄, heat
What is the observation when Fehling’s reagent is used to distinguish aldehyde or ketone?
- aliphatic aldehyde: brick red ppt. of Cu₂O formed
- ketone/aromatic aldehyde: no brick red ppt. formed
What is the observation when Tollens’ reagent is used to distinguish aldehyde or ketone?
- aldehyde: silver mirror formed
- ketone: no silver mirror formed
- *methanoic acid gives false positive result
What is the observation when acidified K₂Cr₂O₇, heat is used to distinguish aldehyde or ketone?
- aldehyde: orange to green
- ketone: remains orange
What is the observation when acidified KMnO₄, heat is used to distinguish aldehyde or ketone?
- aldehyde / aryl ketone: purple KMnO₄ decolourises
- aliphatic ketone: purple KMnO₄ remains purple
What is the distinguishing test for carboxylic acids?
positive test result, equation
Test: Add Na₂CO₃ (aq), bubble gaseous products into limewater
Positive test result: effervescence observed, white ppt. formed with limewater
Equation: RCOOH (aq) + Na₂CO₃ (aq) → RCOO⁻Na⁺ (aq) + CO₂ (g) + H₂O (l)
What is the distinguishing test for phenylamine?
Test, positive test result
Test: a few drops of Br₂ (aq)
Positive test result: Orange Br₂ (aq) turned colourless, white ppt. formed
What is the distinguishing test for amide?
Test, positive test result, equation
Test: boil with NaOH (aq)
Positive test: NH₃ (g) evolved
Equation: RCONH₂ (aq) + NaOH (aq) → RCOONa (aq) + NH₃ (g)
What is the distinguishing test for ammonium salt of carboxylic acid?
Test, positive test result
Test: NaOH (aq), warm
Positive test result: NH₃ (g) evolved
What is the test for aliphatic amines? (not distinguishing test)
Test, positive test, equation
Test: moist red litmus paper
Positive observation: fishy odour, moist red litmus turns blue
Equation: RNH₂ + H₂O → RNH₃⁺ + OH⁻
What is the test for salt of amines? (not distinguishing test)
Test, positive test, equation
Test: Add NaOH (aq), test with moist red litmus paper
Positive observation: fishy odour, moist red litmus turns blue
RNH₃⁺ + OH⁻ → RNH₂ + H₂O
