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Aldehydes, Ketones, and Carboxylic Acids — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryAldehydes, Ketones, and Carboxylic Acids3 Marks
Question
Answer the following question:
Give chemical tests to distinguish between:
  1. Acetaldehyde and benzaldehyde.
  2. Propanone and propanol.
✓

Answer

  1. Acetaldehyde reacts with $NaOI (I_2/ NaOH$) to form yellow ppt of iodoform while benzaldehyde does not give this test.
$\text{CH}_3-\text{CHO}\ +\ 3\text{NaOI}\ \rightarrow\ \text{HCO ONa}\ +\ \text{CHI}_3\downarrow\ +\ 2\text{NaOH}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Iodoform}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{(Yellow ppt.)}$
  1. Propanone gives orange-red ppt with 2, 4-DNP reagent and yellow precipitate of iodoform with sodium hypoiodite, whereas 1-propanol does not give these tests.
$\text{CH}_3-\text{COCH}_3\ +\ 3\text{NaOI}\ \rightarrow\ \text{CHI}_3\downarrow\ \\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{Iodoroem}\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ^\text{(Yellow ppt.)}\\+\ \text{CH}_3\text{COO Na}^+\ +\ 2\text{NaOH}$

$\text{CH}_3-\text{CH}_2-\text{CH}_2-\text{OH}\ \xrightarrow{\ \text{N}_2\text{OI}\ }\ \text{No yellow ppt. of iodoform}$

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