Question: From NCERT SubTopic:Alcohols: Preparation & Properties Derived PYQ

n-Propyl alcohol and iso-propyl alcohol can be distinguished by -

1. ${PCl}_{5}$

2. reduction

3. oxidation with potassium dichromate

4. ozonolysis

Answer ▽

3.oxidation with potassium dichromate

The first option PCl5 as we know is a chlorinating agent. On reacting n-propyl alcohol and iso-propyl alcohol with PCl5, both the OH will be replaced by Cl atom. So PCl5 cannot be used to distinguish between them.

We know that OH is not a good leaving group and thus it cannot be easily reduced to alkanes. The OH group is first converted into other easy leaving groups (maybe by treating with PCl5 ) and then it is reduced to alkanes. Therefore, a reduction cannot be used to distinguish between n-propyl alcohol and isopropyl alcohol.

We know that acidified potassium chromate is an oxidizing agent.

On treating n-propyl alcohol with acidified potassium dichromate, we get an aldehyde

CH3CH2CH2OH + K2Cr2O7 + H + →CH3CH2CHO + H2O + Cr3 +

We already discussed that isopropyl alcohol is a secondary alcohol. On treating secondary alcohol with potassium dichromate in an acidic medium, it acts as an oxidation agent and gives propanone (ketone) as the product.

CH3COCH3

Thus, n propyl alcohol and isopropyl alcohol give different products on oxidation with potassium dichromate. Therefore, this reagent can be used to distinguish between the two.

Ozonolysis is the addition of Oxygen to alkenes or alkynes and making it saturated. Therefore, it cannot be used to distinguish between them.

Thus, the correct option is C.

Note: There are various other distinguishing steps. Some of them are treated with Fehling's reagent, Tollen’s reagent, Schiff reagent, and benedict solution. These are some of the reactions that aldehydes undergo but ketone does not. On adding Schiff’s reagent, if there is a change in the pink color, it means that aldehyde is formed. This shows the presence of primary alcohol. It shows the absence of primary alcohol if there is no change in the pink color. Another test is the iodoform test which is answerable only by ketone. If it gives the iodoform test, it shows the presence of secondary alcohol.

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Question: From NCERT SubTopic:Alcohols: Preparation & Properties Derived PYQ

The reaction of ethyl formate with an excess of CH3MgI followed by hydrolysis gives-

1. n-Propyl alcohol

2. Ethanol

3. Isopropyl alcohol

4. Propanal

Answer ▽

3. Isopropyl alcohol

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Question: From NCERT SubTopic:Alcohols: Preparation & Properties Derived PYQ

Propene, CH3-CH=CH2 can be converted into 1-propanol by oxidation. Indicate which set of reagents amongst the following is ideal to effect the above conversion?

1. KMnO4(alkaline)

2. Osmium tetroxide (OsO4/CH2Cl2)

3. B2H6 and alk H2O2

4. O3/Zn

Answer ▽

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Question: From NCERT SubTopic:Alcohols: Preparation & Properties Derived PYQ

Lucas reagent is-

1. conc. HCl and anhy. ZnCl2

2. conc. HNO3 and anhy. ZnCl2

3. conc. HCl and hydrous ZnCl2

4. conc. HNO3 and hydrous ZnCl2

Answer ▽

Lucas reagent is a mixture of anhydrous $Z n C l_{2}$ and conc. $H C l$ is used for the distinction of monohydric alcohol. Tertiary alcohols on addition produce a precipitate immediately while secondary alcohols produce ppt. after 5 minutes. Primary alcohols do not produce any precipitate. Therefore, assertion is true but reason is false

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Question: From NCERT SubTopic:Alcohols: Preparation & Properties Derived PYQ

The number of primary alcohol isomers of C5H11OH is -

1. 5

2. 4

3. 2

4. 3

Answer ▽

2. 4

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Question: From NCERT SubTopic:Alcohols: Preparation & Properties Derived PYQ

The decreasing order of boiling points of $1 °$ , $2 °$ , and $3 °$ alcohol is-

1. $1 °$ > $2 °$ > $3 °$

2. $3 °$ > $2 °$ > $1 °$

3. $2 °$ > $1 °$ > $3 °$

4. None of the above

Answer ▽

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Question: From NCERT SubTopic:Alcohols: Preparation & Properties Derived PYQ

The most effective reagent used to converts but-2-enal to but-2-enol is-

1. KMnO4

2. NaBH4

3. H2/Pt

4. K2Cr2O7/H2SO4

Answer ▽

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Question: From NCERT SubTopic:Alcohols: Preparation & Properties Derived PYQ

Which is the best reagent among the following to convert but-2-yne to trans-but-2-ene?

H_{2} / P d

-charcoal

H_{2} / Raney nickel

H_{2} / P d - B a S O_{4}

N a / liq . N H_{3}

Answer ▽

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