12th Class Chemistry Short Questions Preparation for Pakistani Students

Question # 1

What are the primary pollutants?

Ans 1: The waste product given out from chimneys of industrial units and exhaust of automobiles may contain gases such as sulphur dioxide.sulphur trioxide,nitrogen oxides,carbon monoxide compound of fluorine and radioactive material .The waste products are called primary pollutants.

Question # 2

Define open chain compound.

Ans 1: Open chain may be branched or non branched .Open chain hydrocarbons are also called aliphatic compounds.
Branched chain compounds: Those organic compounds in which the carbon atom are attached on the side of the chain.

Question # 3

Write a note on Lucas Test?

Ans 1: 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 :
1. Tertiary alcohol form an oily layer immediately.
2. Secondary alcohols for an oily layer in five to ten minutes.
3. Primary alcohols form an oily layer only on heating.

Question # 4

Write importance of cracking.

Ans 1: Besides increasing the yield of gasolines,cracking has also produced large amount of useful by products,such as 60 ethane,propane,butane and benzene.These are used for manufacturing drugs,plastic ,detergents ,synthetic fibres,fertilizers weed killer and important chemical like ethanol,phenol and acetone.

Question # 5

Why Alkynes are less reactive than alkenes towards Electrophilic Regents?

Ans 1: A sigma-bond in alkenes is not only weak but its electrons are more expose to an attack by an electrophilic reagent.Both these acts make the alkenes a very reactive class of compounds. Alkynes although contain two sigma-bond are less reactive than alkenes towards electrophilic reagents this is because the bond distance between the two triple bonded carbon atoms is very short and hence the sigma-electrons are not available to be attacked by electrophilic reagents.

Question # 6

How semiconductors are used in transistors?

Ans 1: Semiconductors may joined to other material,which may be a metal or a different semiconductor.The junction between the different materials form a boundary.It allows electricity to pass more properly and is used in transistors.

Question # 7

What reaction were taking place in the first 24 hour during setting of cement?

Ans 1: A short time after the cement is mixed with eater tricalcium aluminate absorbs water and forms a colloidal gel of the composition,
The gel starts crystallizing slowly,reacts with gypsum to form the crystal of calcium sulphoaluminate.

Question # 8

Write down th formula of the Superphosphate and triple phosphate?

Ans 1: Superphosphate :Ca(H₂PO₄)₂
triple phosphate: (NH₄)_2HPO4

Question # 9

Give chemical reaction for preparation of Bakelite?

Ans 1: 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 # 10

What are aromatic hydrocarbons?Give two example.

Ans 1: The carbocyclic compounds containing at least one benzene ring,six carbon atoms with three alternate double and single bonds are called aromatic hydrocarbons.These bonds are usually shown in the form of a circle.
Examples: Toluene,Phenol and Nitrobenzene.

Question # 11

Define lignin?Write its effect on paper?

Ans 1: Lignin is an aromatic polymer and causes paper to become brittle.
Wet sheet is dried in drying section of machine with the help of rotary drum,Water is separated from fiber either by gravity by section or by pressing or by heating,.

Question # 12

What is difference between peptide and protein?

Ans 1: Peptides are the compound formed by the condensation of two or more same or different a amino acids,.The condensation occurs between amino acids with the elimination of water.
The formation of peptide bonds can continue until a molecule containing several hundred thousands amino acids is formed,Such a molecule is called polypeptide or protein.

Question # 13

Give reason for the development of colours in the transition complexes?

Ans 1: In transition example ,the d-orbits are responsible for the colour development in their compounds,When these orbitals are involved in bonding,they split up residing in low energy d orbitals absorb a part of the visible light and jump to the high energy d orbital,This process is called d-d transition.

Question # 14

What is the general pattern of reactivity of benzene towards electrophone?

Ans 1: The highly stable delocalized electron of benzene ring not radley available for the nucleophilic attack like the electrons of alkenes.Therefore the electron of benzene ring do not assist in the attack of weal electrophiles,It means that more powerful electrophiles are required to penetrate and break the continuous sheath of electron cloud in benzene.

Question # 15

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 # 16

Give four common properties of group IVA elements of periodic table.

Ans 1: i) All the elements of this group show a valency of four.
Ans 2: ii) All of them form hydrides,MH₄.
Ans 3: iii) They form tetrachlorides,MCI₄.
Ans 4: iv) They also form the oxides,MO₂

Question # 17

What is the role of Gypsum in Agriculture.

Ans 1: Role of Gypsum in Agriculture: Gypsum is applied to the soil as source of calcium and sulphur. The calcium supplied by gypsum in fertilizer is of importance in crop production in area where soils are subject to extensive leaching. Sulphur compounds had been applied to soils because of their observed beneficial effect on plants,sulphur has an influence on chlorophyll development in plant leaves.Although not a constituent o chlorophyII,plants deficient in sulphur exhibits a pale green color.The root system of several plants have been observed to be greatly enlarged by the application of sulphur containing materials such as gypsum.

Question # 18

Branched hydrocarbons are better as a fuel as compared to straight chain?

Ans 1: Straight chain hydrocarbons have low octane numbers and make poor fuels.

Question # 19

Give reaction of Aluminium with dilute and concentrated H₂SO₄?

Ans 1: Reaction with dilute H₂SO₄:Aluminium does not react with dilute sulphuric acid.
Ans 2: Reaction with Conc.H₂SO₄: Al is oxidized by hot concentrated sulphuric acid to liberate sulphur dioxide gas.
2Al_(s)+ 6H₂SO_4(aq)----->Al₂(SO₄)_3(aq)+ 3H_2(g)

Question # 20

Write names and formulas of oxyacids of nitrogen.

Ans 1: Name Formula
1.Nitrous Acid HNO_{2
2. Nitric Acid}HNO₃

Latest Educational News Stories

Pakistan's Largest Database of Colleges and Universities

BS Programs

University Past Papers

University Results

Exam Results 2024

Study Abroad Programs and Opportunities for Pakistani Students