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12th Class Chapter 12 Chemistry Short Questions

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Question: 1
Write three uses of formaldehyde?
Answer: 1
1-34
  1. It is used as decolouring agent in vat dyeing.
  2. It is used in the silvering of mirrors.
  3. It is used in making medicines urotropine used as urinary antiseptic.
Question: 2
What is sodium nitroprusside test?
Answer: 2
2-34
Ketones produce a wine red or orange red color on adding alkaline sodium nitroprusside solution drop wise,Aldehyde don't give this test.
Question: 3
What is sodium bisulphate test?
Answer: 3
3-34
Sodium bisulphate test: Aldehydes and small methyl ketons from a crystalline white precipitate with saturated sodium bisulphite solution.
Question: 4
What is Benedict solution test?
Answer: 4
4-34
Aliphatic aldehydes form a brick red precipitate with benedicts solution to an aldehyde solution add Benedict;s solution and coil A brick red precipitate of curprous oxide is formed.
Question: 5
What is Formalin?
Answer: 5
5-34
Methyl alchohol is oxidized to gaseous formaldehyde which is absorbed in water,The resulting mixture is called formalin.Formalin is a mixture of 40% formaldehyde ,8% methyl alchohol and 52% water.
Question: 6
Fehling solution reacts with aldehydes to give red ppt,Justify it?
Answer: 6
6-34
Aliphatic aldehydes form a brick red precipitate with Fehling solution,To an aldehyde solution and Fehling solution and boil .A brick red precipitate of cuprous oxide id formed. Ketones do not give this test,.
Question: 7
Write the name of those weal oxidizing agents which can oxidize aldehyde but not the ketone?
Answer: 7
7-34
Tollen's reagent ,Fehling solution and Bendict's solution.
Question: 8
Which products are formed by the catalytic reduction of aldehydes?
Answer: 8
8-34
Aldehyde and ketones on reduction with hydrogen in the presence of a metal catalyst like Pd,Pt or Ni form primary and secondary alcohols respectively.Hydrogen is added across the carbonyl group.
Question: 9
What is Tollen's Test?
Answer: 9
9-34
Aldehydes form silver mirror with Tollen's reagent (ammonical silver nitrate solution).Add tollen's reagent to an aldehyde solution in a test tube and warm,A silver mirror is formed on the inside of the test tube.
Question: 10
What is silver mirror test?What is its improvement?
Answer: 10
10-34
Aldehyde form silver mirror with Tollen's reagent .Add Tollen's reagent to aldehyde solution in a test tube and war,.A silver mirror is formed on the inside of the test tube.
Question: 11
How a-hydrogen acids are produced from aldehyde an ketones?
Answer: 11
11-34
a-hydrogen acids are produced from aldehyde and ketones by oxidation process using strong oxidizing agents .The oxygen atom attached to the carbonyl group in aldehydes is oxidizing to OH group.
Question: 12
Write down some used of acetaldehyde?
Answer: 12
12-34
It is used to make acetaldehyde ammonia used as rubber -accelerator,.It is used as antiseptic inhalant in nasal infections.It is used in silvering of mirrors.
Question: 13
How aldehyde reacts with hydrdzine?.
Answer: 13
13-34
Aldehyde react with phenyl hydrazine to form phenylhydrazone in the presence of an acid.
Question: 14
Define Aldol condensation.
Answer: 14
14-34
Aldehydes and ketons possessing a-hydrogen atoms reacts with cold dilute solution of an alkali to form addition products known as aldols,The name aldols is given to the products because it contain both aldehyde and alcohol functional groups,In this process two molecules of the same carbonyl compound condense to form an aldol.
Question: 15
Write chemical formulas of hydroxylamine and phenyl hydrazine.
Answer: 15
15-34
Chemical formula of hydroxylamine: NH2OH
Chemical formula of phenyl hydrazine.:C6H5NHNH2
Question: 16
How does an aldehyde react with
1.Hydroxylamine 2.Hydrazine
Answer: 16
16-34
1.Hydroxylamine:Aldehyde reacts with hydroxylamine to form oxims in the presence of an acid.
2.Hydrazine : Aldehyde reacts with hydrazinetoform hydrazone in the presence of acid.
Question: 17
Describe the mechanism of base catalyst nucleophillic addition to a carbonyl compound?
Answer: 17
17-34
A base catalyzed nucleophilic addition will take place with strong nucleophilic reagent which has general mechanism.
Question: 18
Write a reaction which is used to protect aldehyde group against alkaline oxidizing agent?
Answer: 18
18-34
Acetaldehyde combine with alcohol in the presence of hydrogen chloride gas to form acetals.The hydrogen chloride gas acts as a catalyst.Both the alcohols and the hydrogen chloride gas must be dry.This reaction is used to protect the aldehyde group against alkaline oxidizing,
Question: 19
How will you distinguished between ethanal and propanal?
Answer: 19
19-34
Ethanal forms yellow precipitate of iodoform with an alkaline solution of iodoine,Propanal will not give this test.
Question: 20
Give formula of formaldehyde and acetaldehyde.
Answer: 20
20-34
Formula of formaldehyde : HCHO
Formula of acetaldehyde: CH3CHO
Question: 21
Define nucleophilic addition reaction with an example?
Answer: 21
21-34
Addition of nucleophillic reagent to the substrate in the presence of some catalyst is called nbucleophilic addition reaction.It is due to the unsymmetrical electronics configuration about the carbonyl group,the nucleophilic reagent can start the initial attack on the carbon.
Question: 22
Addition of HCN on aldehydes and ketones is abase catalyzed reaction?
Answer: 22
22-34
Hydrogen cyanide adds to aldehydes and ketones to form cyanohydrines. The reaction is carried out by adding slowly a mineral acid to an aqueous solution of sodium cyanide,The acid generates HCN from sodium cyanide in SItu.
Question: 23
What is iodoform test?
Answer: 23
23-34
The haloform reaction using iodine and aqueous sodium hydroxide is called the iodoform test. It results in the formation of water insoluble iodoform which is yellow solid,iodoform test is used for distinguish ,ethyl ketones from other ketones.
Question: 24
How will you distinguish between acetaldehyde and benzaldehyde?
Answer: 24
24-34
Acetaldehyde is an aldehyde having a hydrogen atom which react with cold dilute solution of an alkali to form product known as aldol,While benzaldehyde is an aldehyde having no a hydrogen atom so under which reacts with cold dilute solution of an alkali to form product known as Cannizzaro product.
Question: 25
Write down mechanism of Cannizzaro reaction?
Answer: 25
25-34
The hydroxid ion act as a nucleophile. It attacks ion the electrophile carbonyl carbons to form a complex anion.
Question: 26
What is the difference between aldhydes an ketones?
Answer: 26
26-34
Aldehydes: In aldehydes,the cabonyl group is bonded to at leat one hydrogen atom,and so occurs at the end or a chain,An aldehyde can be represented by the general formula.
Question: 27
Give industrial preparation of acetaldehydes?
Answer: 27
27-34
Acetaldehyde is prepared industrially by air oxidation of ethylene using palladium chloride with a cupric chloride promoter.
Question: 28
Justify that Cannizzaro reaction is self oxidation-reduction reaction?
Answer: 28
28-34
Cannizzaro reaction is a disproportion reaction.two molecules of the aldehyde are involved one molecule being converted into the corresponding alcohol (the reduce product)and the other into the acid in the salt form(the oxidation process).
Question: 29
What is the use of iodoform test to distinguish between acetaldehyde and formaldehyde?
Answer: 29
29-34
The haloform reaction using iodine and aqueous sodium hydroxide is called the iodoform test,It results in the formation of water insoluble iodoform which is a yallow solid,Iodoform test is used for distinguish acetaldehyde from other aldehydes,
Question: 30
Explain one method of formation of formaldehyde form methyl alchohol.
Answer: 30
30-34
Formaldehyde is prepared in laboratory by passing a mixture of methyl alcohol vaporous and air over plantinized asbestos or copper or silver catalyst at 300 C.Acetaldehyde is prepared in laboratory by the oxidation of ethyl alchohol with acidified sodium dichromate solution.
Question: 31
How formaldehyde is prepared on industrial scale?
Answer: 31
31-34
Formaldehyde is manufactured by passing a mixture of methanol vaporous and air over iron oxide molybdenum oxide or silver catalyst at 500 C.
Question: 32
How acetals are formed?
Answer: 32
32-34
Acetaldehyde combine with alcohols in the presence of hydrogen chloride gas to form acetyl,The hydrogen chloride gas acts a catalyst .Both the alcohol and the hydrogen chloride gas must be dry.
Question: 33
What is Cannizzaro reaction?
Answer: 33
33-34
Aldehydres that have no a hydrogen atom under cannizaro reaction,cannizzaro reaction is a disproportional (self oxidation and reduction reaction).two molecule of the aldehyde are involved one molecule being converted into the corresponding alcohol and the other into the acid in the salt form (the oxidation product).
Question: 34
What is halofrom reaction?
Answer: 34
34-34
Acetaldehyde and methyl ketones react with halogens in the presence of sodium hydroxide to give haloform this reaction is called haloform reaction,The term haloform is used for the distinguish acetaldehyde fromother aldehydes.

12th Class Chemistry Chapters Short Questions