12th Class Chemistry Short Questions Preparation for Pakistani Students

Question # 1

The sigma bonds are inert in alkanes.Explain?

Ans 1: In the alpha bond the electrons are very tightly held between the nuclei which make it very stable bond,A lot of energy is required to break it.The alkanes or paraffins under ordinary condition are inert towards acid,alkalis,oxidizing and reducing agents.

Question # 2

What do you know about reducing smog and oxidizing smog?

Ans 1: The smog contain high content of So₂it is chemically reducing in nature and is known as reducing smog,The main cause of reducing smog is combustion of coal.Photochemical smog consists of higher concentration of oxidants like ozone and is also termed as oxidizing smog,

Question # 3

Name organic compound first of all prepared in the laboratory and how?

Ans 1: Friedrick Wohler synthesized urea,an organic compound from ammonium cyanate ,a substance of known mineral origin.
NH₄CNO ---------- (NH₂)₂CO

Question # 4

Write down important use of lipids?

Ans 1:
1. Lipids are good source of energy and make the food more palatable.
2. Lipids exert an insulting effect on the nervous tissues,.
3. Lipids are good energy reservoirs in the bofy,

Question # 5

Ionization energy of Al³⁺is greater than Mg²⁺.Give the reason.

Ans 1: By moving from left to right in a period,the outer shell remains the same,while the nuclear charge increases effectively that makes the removal of an electron difficult and hence the value of ionization energy increases.Similarly the size of Al is smaller than Mg so Al³⁺it has greater ionization energy than Mg²⁺.

Question # 6

Write a note on Cholesterol?

Ans 1: It is the most abundant animal sterol occur in all animals tissues but it is only in a few higher plants,Cholesterol is present both in the free as well as esterified from in the blood,animals tissues ,egg an yolk,various and fatd and nerve tissue.

Question # 7

Differentiate between homocyclic and heterocyclic compounds?

Ans 1: The compounds in which the ring consists of only carbon atom,These are called carbocyclic compounds,Homocyclic Alicyclic compound are further classified as
1. Alicyclic compound
2. Aromatic compound
Heterocyclic compound: The compound in which the ring consists of atom of more than one kind are called heterocyclic compound,In heterocyclic compound generally one or more atom of element such as nitrogen,oxygen or sulphur are present.

Question # 8

How does an aldehyde react with
1.Hydroxylamine 2.Hydrazine

Ans 1: 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 # 9

What are Chelate and what they contain?

Ans 1: Chelate: When all the donor atoms of a polydentate ligand get coordinated with the same metal ion,a complex is formed which contain one or more rings in its structure and hence is called Chelate.

Question # 10

Why vital force of theory is rejected?

Ans 1: Vital force of theory was rejected by Friedrich Wohler when he synthesized urea an organic compound from ammonium cyanate a substance ok known mineral origin.
Since the synthesis of urea from ammonium cyanate ,million of organic compounds have been prepared and analyzed.

Question # 11

Write down any two characteristics feature of organic compound?

Ans 1: Non Ionic Character of Organic Compound:Organic Compounds are generally covalent compound ,therefore do not give ionic reaction.
Isomerism:Isomerism is a very common phenomena in organic compounds.very often more than one compound are represented by the same molecule formula.However they have different structural formulas.

Question # 12

What is Vital force of theory?

Ans 1: Early scientist believe that the organic compound could be manufactured only by and within living thing and these compounds could be synthesized from inorganic material this theory was referred to as Vital force theory.

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

How do leather tanneries pollute the water?

Ans 1: Many leather tanning units,varying from the cottage scale to big industrial units are working in and around many big cities of Pakistan.They use large quantities of chromium salts for leather tanning,They are producing goof variety of exportable leather but only some units has facing the facilities of waste water treatment by reducing Cr into trivalent state followed by alkaline precipitation by of Cr(OH)3.These industries are the big source of chromium pollution on the environment ,Chromium is highly toxic an is known cause cancer.

Question # 15

What are ferons and Teflons?

Ans 1: Ferons: Fluorine is used for the preparation of freons,Freons is the commercial name of low molecular mass fluoro chloro carbons.These are being used as the refrigerants and aerosol propellants.
Teflons:Fluorine is used for the preparation of Teflon,It is polymerized tetrafluoroethylene compound.It is valuable plastic which resists the action of oxidants,acid and alkalies.

Question # 16

Under what conditions aluminium corrodes?

Ans 1: When aluminium sheet is exposed to moist air it acquires a thin,continuous coating of aluminium oxide,which is product of aluminium corrosion.

Question # 17

Define resonance energy?What is the resonance energy of benzene?

Ans 1: Benzene is more stable than the hypothetical 1,3,5-cyclohexatriene by 150.5 kj/mole.This difference between amount of heat is actually released and that calculated on the basis of the Kekule structure is called Resonance Energy Benzene shows the phenomenon of resonance which makes it more stable than others.In benzene electrons are delocalized making it a very stable molecule.The resonance energy of benzene is 150.5 kj/mole

Question # 18

How Clay Articles are glazed?

Ans 1: Clay articles are glazed by boric acid because borate glazes possesses a higher coefficient of expansion.

Question # 19

What is smog?What are the content of photochemical smog?

Ans 1: The word smog is combination of smoke and fog,Photochemical smog consists of higher concentration of oxidants like ozone and is also termed as oxidizing smog,The main reactants of photochemical smog are nitric oxide NO and unburnt hydrocarbons,Nitric acid is oxidizing to nitrogen dioxide within minutes to hours depending upon the concentration of pollutants gas.

Question # 20

What is landfill?

Ans 1: The municipal solid waste is mainly disposed off by dumping it in landfill,The landfill is large hole in the ground or even a bare piece of land when the landfill becomes full with water it is covered by soil or clay.,

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