12th Class Chemistry Short Questions Preparation for Pakistani Students

Question # 1

Discuss effect of temperature and pH on enzyme activity?

Ans 1: The enzymatic reaction occurs best at or around 37 Degree which is the average normal body temperature,The rate of chemical reaction is increased by a rise in temperature but this is only over a limit range of temperature,The enzymes usually destroyed at high temperature,the activity of enzyme is reduced at low temperature.The temperature at which an enzyme reaction occurs the fastest is called it optimum temperature.

Question # 2

What is peptide bond?

Ans 1: The formation of peptide bonds can continue until a molecule containing several hundred thousand amino acids is formed ,Such a molecule is called polypeptide or protein.

Question # 3

How detergent are treat to aquatic animal?

Ans 1: Detergents are excessively used in industry and household as cleaning agents,The amount of disposed detergent in waste water is increasing day by day,This waste water when discharged in rivers,sea ,greatly affects the aquatic life.Detergent content of waste water mobilize the bound toxic ions of heavy metals.

Question # 4

Write down nitration and sulphonation of benzene?

Ans 1: The introduction of NO₂group in benzene ring is called Nitration,.The nitration of benzene takes place when it is heated with a 1:1 mixture of conc.HNO₃and conc.Sulphuric at 50-55 degree acid reacts with nitrir acid to generate nitronium ion.

Question # 5

How hydrolysis of ester leads the formation of acetic acids?

Ans 1: The ester on boiling with concentrated sodium hydroxide yields sodium salt of the acid,This resulting salt when treated with dilute HCI gives the free carboxylic acid.

Question # 6

How will you distinguished between ethanal and propanal?

Ans 1: Ethanal forms yellow precipitate of iodoform with an alkaline solution of iodoine,Propanal will not give this test.

Question # 7

What is the effect of Acid rain on earth?

Ans 1: Acidification of the soil and rocks can leach metals like aluminium ,mercury ,lead and calcium and discharges them into water bodies.These heavy metals are accumulated in the fished and are health hazards for human and birds they eat these fishes,The elevated concentration of aluminium is harmful for fished as it clogs the gills this causing suffocation,Acidification of the soil can also each nutrient thus damaging leaves and plants and growth of forest.

Question # 8

Why 1^stelectron affinity is negative and 2^ndis positive?

Ans 1: Energy is usually released when electronegative elements absord the first electron and E.A in such case is expressed in negative figure,as in the case of halogens,when a second electron is added to a uni negative ion,the incoming electrons is repelled by the already present negative charge and energy in this process is represented by +ve sign
Ans 2: O+e^------->O^- E.A₁=-141 kj mol^-1O^-+e^-------->O^-2 E.A₂=+780 kj mol^-1

Question # 9

What is reaction of heat on orthoboricacid,H₃BO₃?

Ans 1: When orthoboric acid is heated strongly,it swells to frothy mass losing water molecules.It is first converted into metaboric acid then to tetra boric acid and finally to boric anhydride.
Ans 2: H₃BO₃----->HBO₂+ H₂O
HBO₂------->H₂B₄O₇+ H₂O
H₂B₄O_7------>2B₂O₃+ H₂O

Question # 10

State procedure by which surface of stoneware is made less porous?

Ans 1: Stoneware are usually glazed to give it a less porous surface by throwing salt upon the articles while they are hot.This treatment produces sodium aluminate and sodium aluminium silicate,which melt readily and cover the entire surface.When the article cools,the covering solidifies,producing a compact,smooth,waterproof surface.

Question # 11

What is the role of stability of carbonium ion in deciding the Mechanism of substitution reaction.

Ans 1: The first step involve the breakage of covalent bond so it is slow step as compared to the second step which involves the energetically favourable combination of ions.The first step is therefore called the rate determining step.The mechanism is called unimolecular because one molecule takes part in the rate determining step.

Question # 12

How Clay Articles are glazed?

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

Question # 13

Manipulate the term 'Esterification ' using alcohol.

Ans 1: When carboxylic acids are heated in the presence of concentrated sulphuric acid ester are formed this process is called esterification process.

Question # 14

Why nitrogen is important for plants?

Ans 1: Nitrogen is required during the early stage of plant growth for the development of stems and leaves,It is the main constituents of protein ,impar green colour to the leaves an enhance the yield and quality of the plants.

Question # 15

Describe the natural source of methane in atmosphere.

Ans 1: Methane Is and important mean of energy especially for countries like in Pakistan which are deficient in the production of mineral oil and coal.It is a mixture of low boiling hydrocarbons,Major portion of the natural gas is methane.It is so formed by the decomposition of organic matter,

Question # 16

Write a brief note on geometric isomerism?

Ans 1: Such components which possess the same structural formula,but differ with respect to the position of the identical groups in space are called geometric isomers,and the phenomena is known as the geometric isomers.Two carbons atom joined by a single bond are capable of free rotation about it,However when two carbons atom are joined by a double bond,they cannot rotate freely.As a result the relative and give rise to cis-trans isomers.

Question # 17

What are nucleosides and nucleotides?

Ans 1: Nucleosides : A nucleosidesus a combination of nitrogenous base with a sugar ,Depending upon the presence of ribo or deoxyribo ,nucleoside can either be a ribonucleoside or deoxyribonucleoside.

Nucleotides:Nucleotides are the organic molecule that serve as the monomer units for forming the nuclei acid polymer DNA or RNA,DNA carries the genetic information and RNA is involve inputting this information to work in the cell.

Question # 18

Absolute alcohol can not be prepared by fermentation process Why?

Ans 1: 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 # 19

What are fertilizer and what are they needed?

Ans 1: Fertilizers are the substance added to the soil to make up the deficient of essectial elements like nitrogen,phosphorus and potassium require for the proper growth of plants.Fertilizer enhance the natural fertility of the soil or replenish the chemical elements take up from the soil by the previous crops.

Question # 20

What is silver mirror test?What is its improvement?

Ans 1: 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.