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Organic QA Flashcards

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1
Q

What is the distinguishing test for alkanes and what’s the reaction behind it?

Test, type of reaction and equation

A

In dark, orange Br₂(aq) remains orange
In UV light, orange Br₂(aq) decolourises

Reaction: Free Radical substitution
Equation: RH + X₂ → RX + HX

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2
Q

What is the distinguishing test for alkenes and what is the reaction behind it?

Test, type of reaction and equation

A
  1. Test: Br₂ (aq) or Br₂ dissolved in CCl₄
    Positive observation: Orange Br₂ decolourises
    Reaction: Electrophilic addition
    Equation: H₂C=CH₂ + X₂ → CH₂X-CH₂X
  2. 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)
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3
Q

How to distinguish between terminal and non-terminal alkene?

Test, type of reaction and equation

A

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

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4
Q

How to distinguish between methylbenzene and other substituted benzene?

Test, type of reaction and equation

A

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

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5
Q

What is the distinguishing test for ethylbenzene?

A

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

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6
Q

What is the distinguishing test for alkyl halides?

A
  1. 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)

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7
Q

What is the distinguishing test for alcohols?

A
  1. solid anhydrous PCl5
  2. SOCl2
  3. a few drops of enthanoyl chloride
  4. Warm with ethanoic acid and a few drops of conc. H2SO4, pour into water
  5. sodium, evaporate resultant mixture to dryness
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8
Q

What is the test, observation, reaction and equation of alcohol distinguishing test with solid anhydrous PCl5?

A

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

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9
Q

What is the test, observation, reaction and equation of alcohol distinguishing test with SOCl2?

A

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

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10
Q

What is the test, observation, reaction and equation of alcohol distinguishing test with ethanoyl chloride?

A

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

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11
Q

What is the test, observation, reaction and equation of alcohol distinguishing test with ethanoic acid?

A

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

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12
Q

What is the test, observation, reaction and equation of alcohol distinguishing test with sodium?

A

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

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13
Q

How to distinguish between primary or secondary alcohol and tertiary alcohol or phenol?

A

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)

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14
Q

How to differentiate between primary, secondary and tertiary alcohols?

A

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

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15
Q

How to differentiate alcohols and carboxylic acids since carboxylic acids also react with solid anhydrous PCl5 and SOCl2?

A

Alcohols: do not change moist blue litmus paper red
Carboxylic acid: turns moist blue litmus red (pH < 7)

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16
Q

What are the distinguishing tests for phenol?

A
  1. RCOCl, NaOH
  2. ferric chloride
  3. Br2(aq)
17
Q

What is the test, observation, reaction and equation of phenol and RCOCl, NaOH?

A

Observation: sweet smelling substance formed (ester)

Reaction: Acid-base, Condensation

Equations:
Ar-OH + NaOH → Ar-O⁻Na⁺ + H2O

RCOCl + Ar-O⁻ → RCOOAr + Cl⁻

18
Q

What is the test, observation of phenol and ferric chloride?

A

Test: Add one drop of neutral FeCl3
Observation: violet colouration

19
Q

What is the test, observation, reaction and equation of phenol and Br2?

A

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

20
Q

What is the distinguishing test for carbonyl compounds?

A

Test: 2,4-DNPH

Positive test: Yellow ppt.

Reaction: Condensation reaction
Equation: (search online)

21
Q

What is the distinguishing test for methyl carbonyl?

A

Test: Tri-iodomethane (Warm I₂ in NaOH (aq))

Positive test: Pale yellow ppt. with characteristic antiseptic smell

Equation: RCOCH3 + 3I₂ + 4OH⁻ → CHI3 + RCOO⁻ + 3H₂O

22
Q

What is the distinguishing test for aliphatic aldehyde?

A

Test: Fehling’s reagent, warm

Positive test: brick red ppt. of Cu₂O formed

Reaction: Oxidation
Equation: RCHO + 2Cu²⁺ + 5OH⁻ → RCOO⁻ + Cu₂O + 3H₂O

23
Q

What is the distinguishing test for aldehydes?

A

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

24
Q

How to prepare Tollens’ reagent?

A

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.

25
Q

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?

A
  • 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
26
Q

What are the tests to distinguish aldehyde and ketone?

A
  • Fehling’s reagent, warm
  • Tollens’ reagent, warm
  • acidified K₂Cr₂O₇, heat
  • acidified KMnO₄, heat
27
Q

What is the observation when Fehling’s reagent is used to distinguish aldehyde or ketone?

A
  • aliphatic aldehyde: brick red ppt. of Cu₂O formed
  • ketone/aromatic aldehyde: no brick red ppt. formed
28
Q

What is the observation when Tollens’ reagent is used to distinguish aldehyde or ketone?

A
  • aldehyde: silver mirror formed
  • ketone: no silver mirror formed
  • *methanoic acid gives false positive result
29
Q

What is the observation when acidified K₂Cr₂O₇, heat is used to distinguish aldehyde or ketone?

A
  • aldehyde: orange to green
  • ketone: remains orange
30
Q

What is the observation when acidified KMnO₄, heat is used to distinguish aldehyde or ketone?

A
  • aldehyde / aryl ketone: purple KMnO₄ decolourises
  • aliphatic ketone: purple KMnO₄ remains purple
31
Q

What is the distinguishing test for carboxylic acids?

positive test result, equation

A

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)

32
Q

What is the distinguishing test for phenylamine?

Test, positive test result

A

Test: a few drops of Br₂ (aq)
Positive test result: Orange Br₂ (aq) turned colourless, white ppt. formed

33
Q

What is the distinguishing test for amide?

Test, positive test result, equation

A

Test: boil with NaOH (aq)
Positive test: NH₃ (g) evolved
Equation: RCONH₂ (aq) + NaOH (aq) → RCOONa (aq) + NH₃ (g)

34
Q

What is the distinguishing test for ammonium salt of carboxylic acid?

Test, positive test result

A

Test: NaOH (aq), warm
Positive test result: NH₃ (g) evolved

35
Q

What is the test for aliphatic amines? (not distinguishing test)

Test, positive test, equation

A

Test: moist red litmus paper
Positive observation: fishy odour, moist red litmus turns blue
Equation: RNH₂ + H₂O → RNH₃⁺ + OH⁻

36
Q

What is the test for salt of amines? (not distinguishing test)

Test, positive test, equation

A

Test: Add NaOH (aq), test with moist red litmus paper
Positive observation: fishy odour, moist red litmus turns blue
RNH₃⁺ + OH⁻ → RNH₂ + H₂O

Chemistry Practical (4 decks)

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