12th Class Chemistry Chapter 11 Short Questions with Answers Solved

Question: 1

Define Fermentation.

Answer: 1

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Fermentation is a biochemical process which occurs in presence of certain enzymes secreted by microorganism such as yeast,Optimum temperature for the process of fermentation is 25-35 degree,Proper aeration ,dilution of solution and the absence of any preservative are essential conditions for fermentation.

Question: 2

Classify alcohols giving an example for each?

Answer: 2

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Alcohols are classified into monohydric and polyhydric alcohols,Monohydric alcohols contain one -OH group while polyhydric alcohol contain two three or more -OH group and names as dihydric or trihydric.

Question: 3

Why ethyl alcohol is liquid while Ethyl chloride is gas at room temperature?

Answer: 3

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Ethyl alcohol is liquid while ethyl chloride is gas because ethyl alcohol has hydrogen bonding which is present in it but absent in ethyl chloride.

Question: 4

Only 12-14% ethanol can be prepared by fermentation process .Justify?

Answer: 4

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Alcohol obtained by fermentation is only upto 12% an never exceeds 14% because beyond this limit enzymes become inactive,This alcohol is distilled again an again to obtain 95% alcohol which is called rectified spirit.

Question: 5

How ethanol is prepared form Molasses?

Answer: 5

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The residue obtained after the crystallization of sugar from concentrated sugar cane juice is called molasses .It undergoes fermentation in the presence of enzymes present in yeast to give ethanol.

Question: 6

How is methylated spirit prepared?

Answer: 6

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Ethanol is denatured by addition of 10% methanol to avoid its use for drinking purposes,Such alcohol is called methylated spirit,A small quantity of pyridine of acetone may also be added for this purpose.

Question: 7

Define Dihydric and Teihydric Alcohols?

Answer: 7

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Alcohols are classified into monohydric and polyhydric alcohols. Monohydric alcohols contain n-OH group while polyhydric alcohols contain two ,three or more -OH groups and names as dihydric or trihydirc .

Question: 8

Define the preparation of methanol by reaction of Co and H₂?

Answer: 8

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First of all mixture of carbon monoxide and hydrogen is purified,It is compressed under a pressure of 200 atmospheres and taken into a reaction chamber by means of coiled pipers. These vapors are passed through a condenser to get methanol Unreacted gasses are recycled though compressor to reaction chamber.

Question: 9

How ethanol is prepared on industrial scale in the world?

Answer: 9

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Ethanol is prepared on industrial scale world over by the process of fermentation.Fermentation is a biochemical process which occurs in the presence of certain enzymes secreted by microorganism such as yeast.Optimum temperature for this process of fermentation is 25-35 degree.

Question: 10

Explain denaturing of alcohol?

Answer: 10

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Ethanol is denatured by addition of 10% methanol to avoid its use for drinking purposes,Such as alcohol is called methylated spirit.A small quantity of pyrimidine or acetone may also be added for this purposes.

Question: 11

Absolute alcohol can not be prepared by fermentation process Why?

Answer: 11

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Absolute alcohol cannot be prepared by fermentation process because there if moisture in the process,Absolute alcohol can be prepared by the rectified spirit in the presence of CaO which absorb its moisture.

Question: 12

Differentiate between primary and secondary alcohol?

Answer: 12

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Monohydric alcohols are further classified into primary ,secondary and tertiary alcohols. In primary alcohols -OH group is attached with primary carbon atom,In secondary alcohols -OH groups is attached with secondary carbon atom .

Question: 13

How is alcohol denatured to make it unfit for drinking?

Answer: 13

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Ethanol is denatured by addition of 10% methanol to avoid its use for drinking purposes,Such alchohol is called methylated spirit,A small quantity of pyrindine or acetone may also be added for this purposes.

Question: 14

Give any three uses of methyl alcohol?

Answer: 14

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It is used as solvent for fats oils,paints ,varnishes.
It is also used as antifreeze in the radiator of automobile.
It is used for denaturing of alcohol.

Question: 15

How will you distinguish between methanol and ethanol?

Answer: 15

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Ethanol gives iodoform with iodine in the presence of Na-OH,Formation of yellow crystals indicate that the alchohol is ethanol. Methanol does not give idodrom test.

Question: 16

How will you distinguished between 1-propanol and 2-propanol?

Answer: 16

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1-propanol is primary alcohol while 2-propanol is a secondary alcohol.

Primary,Secondary and Tertiary alcohols are identified and distinguished by reacting them with con.HCI is anhydrous ZnCI₂. An oily layer of alkyl halides separates out in these reaction :

Tertiary alcohol form an oily layer immediately.
Secondary alcohols for an oily layer in five to ten minutes.
Primary alcohols form an oily layer only on heating.

Question: 17

How secondary and tertiary alcohols can be distinguished by Lucas Test?

Answer: 17

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Secondary and tertiary alcohols are identified and distinguished by reacting them with con.HCI in an hydrous ZnCI₂,An oily layer of alkyl halides separates out on these reactions.

Question: 18

Write a note on Lucas Test?

Answer: 18

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Primary,Secondary and Tertiary alcohols are identified and distinguished by reacting them with con.HCI is anhydrous ZnCI₂. An oily layer of alkyl halides separates out in these reaction :

Tertiary alcohol form an oily layer immediately.
Secondary alcohols for an oily layer in five to ten minutes.
Primary alcohols form an oily layer only on heating.

Question: 19

Water has higher boiling point that ethanol.Explain.

Answer: 19

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Melting and boiling point of alcohol are higher than corresponding alkanes,Methyl alcohol and ethyl alcohol are liquids while methane and ethane are gases,This is also due to hydrogen bonding which is present in alcohols but absent in alkanes.

Question: 20

Distinguish ethanol and tertiary butyl alcohol by Lucas test?

Answer: 20

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Primary,Secondary and tertiary alcohol are identified and distinguished by reacting them with con,HCI in anhydrous ZnCI2,An oily layer of alkyl halides separated out in these reaction:

1.Ethanol is a primary alchohol which form an oily layer only on heating.

2.Tertiary butyl alcohol is a tertiary alcohol which form an oil layer immediately.

Question: 21

Write formula of carbolic acid and it one use.

Answer: 21

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Carbolic acid: C₆H₅OH

its is poisonous and used as a disinfectant in hospitals and washrooms.

Question: 22

Write four uses of each methanol and ethanol.

Answer: 22

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Methanolis used as solvent for fats oil ,paints ,varnishes,It is also used as antifreeze in the radiators of automobiles and for denaturing of alcohol.

Ethanolis is used as solvent as a drink and as a fuel in some countries.Moreover it is used in pharmaceutical preparation and as preservation for biological specimen.

Question: 23

Distinguish between alcohol and a phenol by chemical reaction?

Answer: 23

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1.Alcohols does not react with bases but phenol reacts and gives salts.

Alcohols reacts with bromine water and phenol reacts to give white ppy of tribromophenol.

Question: 24

What are the essential condition for fermentation?

Answer: 24

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Fermentation is biochemical process which occures in presence of certain enzymes secreted by microorganism such as yeast,Optimum temperature for this process of fermentation is 25-35 degree.Proper aeration,dilution of solution and the absence of any preservative are essential condition for fermentation.

Question: 25

Describe the method for preparation of phenol from sodium salt of benzene?

Answer: 25

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Sodium salt of benzene sulphonic acid reacts with NaOh at 320 Degree to give sodium phenoxide which on treatment with HCI give phenol.

Question: 26

Give chemical reaction for preparation of Bakelite?

Answer: 26

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Phenol reacts with formaldehyde in the presence of acid or alkali to give hydrooxyl benzyl alcohol which on further reaction with other phenol molecules yields a polymer called Bakelite.

Question: 27

Explain acidic behavior of phenol.

Answer: 27

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Phenoxide ion is formed by the dissociation of phenol,The negative charge on oxygen atom can become involved with the pie electron cloud on the benzene ring,The negative charge is thus delocalizes in the ring and the phenoxide ion becomes relatively stable.

Question: 28

How phenol is identified chemically?

Answer: 28

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An aqueous solution of phenol reacts with bromine water to give white ppt of 2,4,6 tribromophenol,Thus the color of bromine is discharged.

Question: 29

Picric acid is phenol which behaves like an acid .Justify.

Answer: 29

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Picric acid is 2,4,6 trintophenol,It is actually phenol but has three nitro groups attached to the benzene ring of phenol,Nitro groups are electrons with drawing in nature,Nitro groups attracts electron to themselves and makes easy for phenolic part to donate easily,so picric acid can donate a proton and behave like an acid .

Question: 30

How phenol can be converted into benzene?

Answer: 30

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Benzene is prepared by the reduction of phenol in the presence of Zn.

Question: 31

Why phenol is acidic while alcohol is not?

Answer: 31

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Phenol is much more acidic than alcohols but less acidic than carboxylic acids,Phenoxide formed by the dissociation of phenol.The negative charge on oxygen atom can become involved with the pie electron cloud on the benzene ring,The negative charge is thus delocalized in the ring and the phenoxide ion becomes relatively stable this type of delocalization is not possible in alcohol.

Question: 32

How does phenol react with alkali?

Answer: 32

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Phenol has a acidic nature ,it reacts with alkalies to form salts.

Question: 33

Conc .HNO₃reacts with phenol to give picric acid how?

Answer: 33

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Picric acid is synthesized by the nitration of phenol,.Phenol reacts with conc HNO₃at different temperature.

Question: 34

How does picric acid synthesis take place?

Answer: 34

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Picric acid is synthesized by the nitration of phenol,Phenol reacts with dil and conc.

Question: 35

How to convert phenol to an alcohol?

Answer: 35

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When hydrogen is passed through phenol at 150C in the presence of Ni catalyst ,It gives cyclogexanol which is an alcohol.

Question: 36

Prepare diethyl ether by Williamson synthesis?

Answer: 36

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Alcohols are reacted with metallic sodium from alkoxides. This alkaloides ion is a strong nucleophile and readily reacts with alkyl halide to produce an ether.

Question: 37

Write down two method for the preparation of phenol?

Answer: 37

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1.Prepare phenol by Dow method:In Dow method chloroenzene is treated with 10% Na OH at 360 degree and 150 atmospheres pressure. Sodium phenoxide is produced which on treating with HCI.

2.Prepare phenol by Sodium salt of benzene sulphonic acid:

Sodium salt of benzene sulphonic acid reacts with NaOh at 320 degree to give sodium phenoxide which on treatment with HCi gives phenol.

Question: 38

Ethers are less reactive than alcohols.Justify

Answer: 38

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Ethers are comparatively inert substance.The reagents like ammonia,alkalies,dilute acids and metallic sodium have no action no ethers on cold state .Moreover they are not oxidized or reduced easily.

On the other hand alcohols can react with reagents due to C-O and O-H bonds.These can be oxidized and reduced ,Alcohols also undergo dehydration reaction.

Question: 39

Why are lower alcohols more soluble in water than higher alcohols.

Answer: 39

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Lower alcohols more soluble in water than higher alcohols because solubility of alcohols is due to hydrogen bonding which is prominent in lower alcohols but diminishes in higher alcohols.

Question: 40

Define the following terms

1. Phenol 2. Oxonium ions.

Answer: 40

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Aromatic compounds which contain one or more OH groups directly attached with carbons of benzene ring are called Phenol,The simplest example of phenol which is also known as Carbolic acid.

Oxonium ion is any oxygen cations with three bonds,The simplest oxonium ion is hydronium ion H₃O+.

Question: 41

Ethanol has higher boiling point than diethyl ether.

Answer: 41

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Ethanol has higher boiling point than diethyl ether because ethanol has strong hydrogen bonding in molecule while ether don't show hydrogen bonding with its molecule.

Question: 42

Ethers belong to an inert class of organics compound.Discuss.

Answer: 42

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