• Written By Sushmita Rout
  • Last Modified 25-01-2023

Test for Alcohols: Formulas, Structures, Various Tests for Alcohol Groups

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Test for Alcohols: Alcohols are organic compounds with the functional group OH, called the hydroxyl group. Ethanol is the most common alcohol widely used in alcoholic drinks as a preservative for biological specimens, fuel (gasoline), and solvent for drugs and paints.

While naming alcohols, the suffix ol is added to the parent chain of the alkane name. The position of the OH functional group is indicated in the name. The numbering of the parent chain is done at the end closest to where the OH is located.

The general formula of alcohol homologous series is CnH2n+1OH, where n=1,2,3..

Alcohol, Formula, Structure

Alcohol - Carbon Number, Formula, Structure
Alcohol – Carbon Number, Formula, Structure

The homologous series of alcohols consists of methanol, ethanol, propanol, and butanol with chemical formulas of CH3OH,CH3CH2OH,CH3CH2CH2OH and CH3CH2CH2CH2OH, respectively, where each successive compound differs from the previous one by a CH2 group.

Study Structure of Alcohol Here

Based on the number of hydroxyl groups attached to the parent chain, alcohols are classified as monohydric (contain only one OH group), dihydric (contain two OH groups) and trihydric (contains three OH groups).

Monohydric - Dihydric - Trihydric
Monohydric – Dihydric – Trihydric

When the OH group is attached to the primary, secondary and tertiary carbon atoms, alcohols are further classified as primary (1), secondary (2), and tertiary (1).

Primary - Secondary - Tertiary
Primary – Secondary – Tertiary

Tests to Distinguish Alcohols from Other Functional Groups

To distinguish alcohols from other functional groups, the following tests are performed-

1. Sodium Metal Test

Alcohols react with active metals like sodium with a brisk effervescence to liberate hydrogen gas. A colourless solution of sodium ethoxide, CH3CH2ONa is left behind.

Sodium Metal Test

The absence of phenyl or carboxyl groups favours this reaction.

2. Phosphorus Pentachloride Test

Alcohol reacts with PCl5 with the evolution of HCl gas. Hydrogen chloride reacts with ammonium hydroxide to form white fumes of ammonium chloride.

ROH+PCl5POCl3+HCl

NH4OH+HClNH4Cl+H2O

3. Ester Test

A fruity-smelling compound called esters is formed when alcohols react with carboxylic acids. The reaction between alcohol and carboxylic acid is known as esterification and is a slow and reversible reaction catalysed by an acid such as concentrated sulphuric acid.

The chemical reaction is given below.

Ester Test

4. Ceric Ammonium Nitrate Test

Alcohols react with ceric ammonium nitrate (NH4)2Ce(NO3)6 to form a pink or red coloured precipitate of alkoxy cerium (IV) complex and ammonium nitrate. The red colour disappears if an excess of ceric ammonium nitrate solution is added to the alcoholic sample

The red colour also disappears after resting the reaction mixture.

The chemical reaction is given below.

Ceric Ammonium Nitrate Test

5. Acetyl Chloride Test

Alcohols react with acid halides to form esters with the liberation of hydrogen chloride gas. The hydrogen chloride gas reacts with ammonium hydroxide to give white fumes of ammonium chloride.

The chemical equation is given below.

Acetyl Chloride Test

6. Iodoform Test

Secondary alcohols, ketones and acetaldehyde show a positive iodoform test. A yellow precipitate of iodoform is formed when the given compound is heated with sodium hydroxide solution and iodine.

The chemical reactions are given below

Iodoform tes

Primary, Secondary and Tertiary Alcohols

1. Lucas Test

Primary, secondary and tertiary alcohols react with Lucas reagent (zinc chloride and concentrated hydrochloric acid) at different rates. This reagent forms a cloud-like appearance on reacting with alcohols. Tertiary alcohols react immediately; secondary alcohols react slowly to form a cloud-like appearance after 5 to 10 minutes. However, there is no reaction with primary alcohols. Alcohols are soluble in Lucas reagent, so a clear solution is obtained, while alkyl chlorides being insoluble results in cloudiness in the solution.

The chemical reactions are given below.

Lucas Test

Cloudiness appears immediately Tertiary alcohols
Cloudiness appears within five to ten minutes Secondary alcohols
Cloudiness does not appear  Primary alcohols

2. Victor Meyer Test

Victor Meyer’s test is an important test to distinguish between primary, secondary and tertiary alcohols. It is an organic compound that has a functional group RC(NO)2=NOH and appears as red colour.

The reagents used in the Victor Meyers test are Hl,Ag(NO)2 and KOH/NaOH.

In the test, three different colours are observed for different alcohols. These are listed below.

Blood Red ColourPrimary Alcohol
Blue ColourSecondary Alcohol
No Colour ChangeTertiary Alcohol

When primary alcohol reacts with the reagents (Hl,Ag(NO)2 and KOH/NaOH) the final product is nitrolic acid. However, with tertiary alcohols, there would be no reaction. Victor Meyer’s test is also known as the Red, Blue and White test.

Tests for Phenolic group

Phenols are compounds that contain a hydroxyl group attached to an aromatic ring. The simplest phenol is C6H5OH. Other examples of phenols are o-cresol, m-cresol, p-cresol, quinol, catechol, resorcinol etc.

Tests for Phenolic group

The following tests can detect the phenolic group:

1. Litmus Test

Phenol is weakly acidic and gives a red colour with blue litmus paper. Phenol dissociates in water to form phenoxide ions and water. This is represented as follows:

Litmus test

2. Ferric Chloride Test

Phenols react with neutral ferric chloride solution to give a coloured complex. For example, phenol gives a complex of violet colour as follows:

Ferric chloride test

Observations:

  1. Resorcinol, o,m,pcresol, give violet or blue colouration.
  2. β-Naphthol gives a green colouration.
  3. α-Naphthol gives pink colouration.
  4. Formic acid and acetic acid give deep red colouration.

3. Liebermann’s Test

Phenol in concentrated sulphuric acid reacts with sodium nitrite to form a deep blue or green coloured complex. The blue or green colour changes to red or brown colour on being treated with water. The red colour is due to the formation of indophenol, which changes to blue or green by adding strong alkali. The blue or green colour is due to the formation of indophenol anion.

Liebermann's test

Note:
This test is not given by Nitrophenols and p-substituted phenols. Among the dihydroxy phenol, only resorcinol gives a positive test.

4. Phthalein Dye Test

Phenols in the presence of concentrated H2SO4 condenses with phthalic anhydride to form phenolphthalein. It gives a dark pink colour with NaOH solution. This is called the phthalein dye test.

o-cresolRed
m-cresolBluish Purple
p-cresolNo Colour
CatecholUsually, blue takes a longer time to appear
ResorcinolGreen Fluorescent Colour of Fluorescein

Tests for Alchol Groups

The Tests for the alcohol group (Distinguishing test from other functional groups) are tabulated below:

TestProcedureObservation
Sodium metal TestReagent: 5% sodium hydroxide solution is prepared by dissolving 5g of solid sodium hydroxide in about 50ml. It is then diluted to 100ml.
The organic compound to be tested is taken in a dry test tube.
To it, 1gm of anhydrous calcium sulfate is added and shaken well. This is done to remove excess water.
To the above solution, a small piece of sodium metal is added. 
A brisk effervescence indicates the presence of an alcoholic group
Ester Test1ml of the organic liquid is taken in a clean, dry test tube.
To the above solution, 1ml of glacial acetic acid and 23 drops of conc. Sulfuric acid is added.
The mixture is heated in a water bath for 10 minutes.
The hot mixture is poured into a beaker containing cold water.
A fruity smell confirms the presence of an alcoholic group.
Ceric Ammonium Nitrate TestReagent: The reagent is prepared by dissolving 20g of ceric ammonium nitrate orange crystals in 200ml of warm dilute nitric acid (2N).
1ml of the given compound is taken in a dry test tube.
A few drops of ceric ammonium nitrate reagent is added to the above solution and shaken. 
A wine red coloured precipitate shows the presence of an alcoholic group
Acetyl Chloride Test2ml of given organic compound is taken in a clean test tube.
To the above solution, 1gm of anhydrous calcium sulfate is added and filtered.
To the filtrate, 3 to 4 drops of acetyl chloride solution is added and shaken well.
A glass rod dipped in ammonium hydroxide solution is brought near the mouth of the test tube.
The formation of white fumes indicates the presence of alcohol
Iodoform TestReagent: 2g of solid potassium iodide is dissolved in about 40ml water. To it, 1g solid iodine is added and shaken. The solution is diluted to 100ml.
1ml of given organic compound is taken in a clean, dry test tube.
1ml of 1% iodine solution is added to it.
A dilute solution of sodium hydroxide solution is added dropwise to the above solution until the brown colour of iodine is discharged.
The mixture is heated gently in a water bath.
The formation of yellow precipitate shows the presence of alcohol

Tests for distinguishing primary, secondary and tertiary alcohols

TestProcedureObservation
Lucas TestDissolve 135g of anhydrous zinc chloride in 100ml of concentrated hydrochloric acid. Shake well and cool.
1ml of the organic compound is taken in a test tube, and to it, 10ml of Lucas reagent is added and shaken well. 
Cloudiness appears immediately Tertiary alcohols
Cloudiness appears within five to ten minutes Secondary alcohols
Cloudiness does not appear  Primary alcohols

Victor Meyer’s TestTo the given organic compound, concentrated hydrogen iodide or red phosphorus and iodine are added.
To the above solution, silver nitrite is added to produce nitroalkane.
Nitroalkane is then treated with nitrous acid (NaNO2+H2SO4) and is made alkaline with potassium hydroxide.
Primary alcohol – Blue red
Secondary alcohol – red
Tertiary alcohol – No change

FAQs on Test for Alcohols

Q.1. Which alcohol gives red colour in Victor Meyer’s test?
Ans:
Primary alcohols or 1 alcohol gives red colour in Victor Meyer’s test.

Q.2. Which alcohol gives Lucas test immediately?
Ans:
Primary alcohols or 1 alcohol will not show turbidity immediately. However, tertiary alcohols or 3 alcohols show turbidity immediately, and they give a positive Lucas test.

Q.3. What is acidic dehydration of alcohol?
Ans:
Alcohol reacts with protic acids and loses a molecule of water to form alkenes. As the reaction involves the removal of the water molecule, these are generally known as dehydration of alcohols. It is an example of an elimination reaction. The rate of the reaction differs for the primary, secondary and tertiary alcohols.

Q.4. What are the qualitative tests for alcohol?
Ans:
The qualitative tests for alcohols are –
(i) Chromic Acid Test (or Jones Oxidation)
(ii) Lucas Test using ZnCl2 and HCl
(iii) Iodoform Test.

Q.5. Which alcohol gives a positive iodoform test?
Ans:
Ethanol is the only primary alcohol to give the triiodomethane (iodoform) reaction. However, secondary alcohols with a methyl group attached to the carbon with the OH group respond positively to this reaction.

Study Preparation of Alcohols Here

We hope this article on tests for alcohols is helpful to you. If you have any queries about this page or in general about the alcohols test, ping us through the comment box below and we will get back to you as soon as possible.

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