12th Class Chemistry Short Questions Preparation for Pakistani Students

Question # 1

Write any four uses of nitric acid?

Ans 1: i) It is used as laboratory reagent.
Ans 2: ii) It is used in manufacturing of explosives.
Ans 3: iii) It is used in manufacturing of nitrogen fertilizers.
Ans 4: iv) It is used to make varnishes and organic dyes.

Question # 2

What is the difference between aldhydes an ketones?

Ans 1: 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.
Ans 2: Ketones: In ketones ,the carbonyl group is bonded to two carbons atoms and so it occurs within a chain,A ketone may be represented by the general formula.

Question # 3

Define Enzymes ,name their two properties?

Ans 1: The reaction catalyst of biological systems produced by living cells and are capable of catalyzing chemical reaction are called enzymes.
Properties of enzymes:
1.Enzymes are protein or contain proteins as essential components and in addition require non protein components which are also essential for their activity.
2.Many enzymes contain vitamins as their co factors for example ,nicotinamide adenine dinucleotide contain nicotinamide vitamin.

Question # 4

Justify that Ethene is more reactive than C₆H_6.

Ans 1: The highly sable ,delocalized electron of benzene ring not readily available for the nucleophilic attack like the electron of alkenes,therefore the electrons of benzune ring do not assist in the attack of weak electrophiles.

Question # 5

Distinguish between Ethene and Acetylene?

Ans 1: Ethene and acetylene both are un-saturated compounds. Ethene contains sigma-bond,having partially fiiled p-orbitals overlap in a parallel fashion.sigma-electron are less firmly held between the nuclie. In ethene a sigma-bond is a weak bond.
Ans 2: In actetylene,the carbon atoms are held together by a triple bond,a o-bond and two sigma-bond.The electron density between the carbon atoms is very high which draws atoms very close to each other.Electron in a triple bond are,therefore,less exposed and thus less reactive towards reagents than ethene.

Question # 6

What is the role of potassium in growth of plants?

Ans 1: Potassium is required for the formation of starch sugar and the fibrous material of the planet.They increase resistance to disease and make the plant strong by helping in healthy root development.Potassium fertilizers are especially used for tobacco,coffee and corn.

Question # 7

What objective were raised on Kekule formula of Benzene?

Ans 1: Kekula formula with three double bonds demands of high degree of unsaturation from benzene while usually it exhibits a saturated character,This benzene yields substitution products readily and from addition products .Benzene is also very stable compound.

Question # 8

What is recycling of raw material?

Ans 1: In recycling some of the used or waster material are not discard after their initial use but are processed so that they can be used again,The purpose of recycling is to converse sources such as raw material and energy.

Question # 9

Describe the mechanism of base catalyst nucleophillic addition to a carbonyl compound?

Ans 1: A base catalyzed nucleophilic addition will take place with strong nucleophilic reagent which has general mechanism.

Question # 10

Give two used of bromine?

Ans 1: Ethylene dibromide added to gasoline to save the engine from lead oxide and leaf sulphate deposits.Bromide is also used as fungicide,Silver bromide is used in photography.

Question # 11

HF is a weak acid while HCI is strong acid.Give reason.

Ans 1: The strength hydrogen halogen bond is very high in HF,The bond strength is reflected in the case of dissociation of hydrogen and halides,Hydrofluoric acid is a week acid due to limited ionization than hydrochloric acid.

Question # 12

Define lipids.

Ans 1: Lipids are naturally occurring organic compounds of animals and plants origin which are soluble in organic solvents and belong to a very heterogeneous group of substance.

Question # 13

Write a short note on cracking of petroleum?

Ans 1: Breaking of higher hydrocarbons having high boiling point into a variety of lower hydrocarbons which are more volatile (low boiling) is called cracking of petroleum.

Question # 14

What happened when ammonium acetate is heated?

Ans 1: When ammonium acetate is heated it produce acid amide.

Question # 15

Define Primary Alkyl Halides and secondary alkyl Halides.

Ans 1: The alkyl halides in which halogen atom halogen atom is attached with carbon which is further atached to one or no carbon atom is called primary alkyl halide.
Secondry alkyl Halide:The alkyl halides in which halogen atom is attached with a carbon which is durther attached to two carbon atom is called secondry alkyl halide.

Question # 16

Explain d-d transmission?

Ans 1: When d orbitals are involved in bonding,they split up into twip energy levels,one set has a higher energy that the other,The electron residing d orbitals.d orbital a part of the visible light and jump to high energy d orbitals,This process is called d-d transition.

Question # 17

How is methylated spirit prepared?

Ans 1: 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 # 18

Define Thermal cracking.

Ans 1: Breaking down of large molecule by heating at high temperature and pressure is called thermal cracking.It is particularly useful in the production of unsaturated hydrocarbons such as ethane and propene.

Question # 19

How Nylon 6,6 can be obtained?

Ans 1: Nylon 6,6 is obtained by heating adipic acid with hexamethylenediamine.Nylon 6,6 derives its name from its starting materials adipic acid and hexamethylenediamine,both of which have six carbons atoms.

Question # 20

Identify the actual product ,when HBr is added to propene.

Ans 1: Propene is an unsymmetrical alkene,According to Markovnikov rule.the negative part of the adding reagent goes to that carbon,constituting the double bond,which has least number of hydrogen atom.

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