Chemistry Test - 14

Explanation-

Iodoform test is used to check the presence of carbonyl compounds with the structure R-CO-CH₃ or alcohols with the structure R-CH(OH)-CH₃ in a given unknown substance.

The reaction of iodine, a base, and a methyl ketone gives a yellow precipitate along with an “antiseptic” smell. It also tests positive for a few specific secondary alcohols that contain at least one methyl group in the alpha position.

Compounds that give positive iodoform test-

• Acetaldehyde
• Methyl Ketones
• Ethanol
• Secondary Alcohols that contain Methyl Groups in Alpha Position

Given data and Analysis:

Ethanol, Ethanal, and Propan-2-ol will give a positive iodoform test whereas Butan-1-ol will not give a positive iodoform test as it is not secondary alcohol.

Butan-2-ol’s structural formula is CH₃CHOHCH₂CH₃.

The hydroxy group is on the second carbon atom, making butan-2-ol a methyl, secondary alcohol. Hence butan-2-ol will give a positive iodoform test 

Methanol is an example of the Alcohol group.

• This liquid is acidic, flammable, colorless and has a distinctive fragrance close to that of ethanol (drinking alcohol).
• Methanol is slightly more acidic than water.
• The order of acidity in aqueous solution is as following:
• CH3OH > H2O > CH3CH2OH > (CH3)2 CHOH
• For an acid to be strong its conjugate base anion has to be very stable. Only then acid will disassociate faster to give hydronium ion.

Hence we can conclude that CH3OH is more acidic.

Explanation:

The formula of ethyl alcohol is C₂H₅OH

In the option, it is given as C₂H₃OH

Explanation:

The molecular formula is C₆H₄OH_2.

Additional Information 

Explanation-

⇒ Lucas test is used to differentiate and categorize primary, secondary and tertiary alcohols using a solution of anhydrous zinc chloride in concentrated hydrochloric acid.

⇒ This solution is commonly referred to as the Lucas reagent.

Primary, Secondary, and Tertiary Alcohols are classified based on their reactivity with the Lucas reagent.

⇒ The reaction that occurs in the Lucas test can be seen as a nucleophilic substitution reaction.

⇒ In this reaction, the Chloride in the zinc-chloride bond is replaced with a hydroxyl group originating from the given alcohol.

Butan-2-ol reacts with Lucas reagent and milkiness appears within 5 min. but 2-methyl propane-2-ol reacts with the same to give milkiness immediately.

Explanation:-

Halogenation Reaction:-

• The addition of halogens (Cl, Br, I, F) to the aromatic compounds is termed a halogenation reaction.
• Benzene reacts with chlorine or bromine in the presence of Lewis acids like AlCl₃, FeCl₃, FeBr₃ etc to give chlorobenzene or bromobenzene.
• Here, these Lewis acids act as a catalyst for the reaction.
• The catalyst initiates the reaction by generating the electrophile, that is, chloronium Cl⁺ and bromonium Br⁺ ions.

Halogenation of  Organic compounds:-

• The parent compound is added to the halogen group by the halogenating agent.
• Here, the reagent of halogenation that is acting as a catalyst is SOCl₂.
• Water will be realized in the given organic reaction.

=  

Concept: 

• This is a type of Reduction Reaction. 
• The reduction is a chemical reaction that involves the gaining of electrons by one of the atoms involved in the reaction between two chemicals.
• Oxidation is the gain of oxygen and reduction in loss of oxygen.​

Explanation:

• When phenol is reacted with zinc dust it forms benzene with zinc oxide as a side product.
• It is because zinc dust is a strong reducing agent. 
• Zinc oxidized itself and become ZnO and reduces phenol to benzene.
• NaOH is just a base and H2SO4 is a strong oxidizing agent and acid.

​Additional Information

Phenol to C6H5COOH (Benzoic acid):

Phenol to C6H5CHO (Benzaldehyde)

Explanation:-

Given,

Phenol is treated with acidified Na₂Cr₂O_7.

Phenol is an electron-rich compound and Na₂Cr₂O₇ is a good oxidizing agent that yields Benzoquinone.

As oxidation is taking place there is an addition of oxygen.

Key Points

Detection of Phenol:

• When phenol is treated with neutral ferric chloride solution, a water-soluble colored complex is formed.
• Different phenols give different colored solutions violet, red, blue, etc.
• Aliphatic alcohols do not give this test.
• This reaction is used to distinguish between alcohols and phenols. The reaction is:

• Hence, FeCl3 is used in the detection of the phenolic group is the correct statement.

Fehling's test:

• It is an alkaline solution of CuSO4 and sodium-potassium tartrate.
• The aldehydes reduce Cu2+ to red cuprous oxide.
• Fehling, Tollen's, and Benedict's tests are used to distinguish between aldehydes and ketones.
• As glucose contains an aldehydic group, it responds to Fehling's test.
• Hence, Fehling Solution is used in the detection of Glucose is the correct statement.

Tollen's Test:

• It is the ammoniacal solution of silver nitrate.
• When aldehydes are treated with Tollen's reagent, they reduce it to the silver mirror of Ag.

• Tollen's test is given by aldehydes and not alkenes. Hence, Tollen's reagent is used in the detection of unsaturation is an incorrect statement.

NaHSO3 test:

• Both aldehydes and ketones respond to this test.
• With sodium bisulfite, aldehydes and ketones form crystalline substances called aldehyde bisulfite and ketone bisulfite respectively.
• Hence, NaHSO3 is used in the detection of the carbonyl group is a correct statement.

Hence, the correct option is 3.

Additional Information

• Unsaturation is detected with the help of Bayer's reagent. 

Explanation:

Victor Mayer's test:

• Victor Mayer's test is performed to distinguish between the primary, secondary and tertiary alcohols. All three alcohols respond differently towards the test.
• In this test, the alcohol under examination is treated as follows:
  • It is treated with red phosphorus and iodine when the hydroxyl group is replaced by iodine to form the corresponding iodide.
  • The iodide is then treated with silver nitrite to get the corresponding nitroalkane.
  • In the last step the solution is made alkaline .
  • Primary alcohols forms nitrolic acid, which on treatment with alkali gives gives blood red colouration.
  • Secondary alcohols form pseudo nitrols which on treatment with alkali forms blue color solution.
  • Tertiary alcohols do not produce any color change.
• The reactions may be summarised as follows:

Hence, in Victor Mayer's test, the primary alcohols give a red colour.