12th Class Chemistry Short Questions Preparation for Pakistani Students

Question # 1

The oxidation state vary in a period,but remain almost constant in a group.Give reason.

Ans 1: The number of electrons in outermost shells goes on changing in periods from left to the right,So oxidation states go on changing.The number of electrons in the outermost shells remains the same in a group,so the oxidation states remains the same.Anyhow,the process of unpairing of electrons may happen in a group and oxidation states may change.

Question # 2

Why pie bond is more reactive than alpha bond?

Ans 1: In the formation of pie bond,the partially filled p-orbitals overlap in a parallel fashion,the probability of finding electron is thus away from the line joining the two nuclei,due to this reason pei electron are less fimely helf between the nuclei.

Question # 3

Give an idea about Clinker.

Ans 1: The resulting product obtained from the kiln is known as cement clinker,This has the appearance of greenish black or grey coloured balls varying in size from small nuts to peas.

Question # 4

How phenol can be converted into benzene?

Ans 1: Benzene is prepared by the reduction of phenol in the presence of Zn.

Question # 5

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 # 6

Define paramagnetic?Which two transition metal ions have strongest paramagnetic behaviour.

Ans 1: The substance which are weakly attracted by a strong magnetic field are called paramagnetic For example Fe²⁺ and Mn³⁺.

Question # 7

How will you distinguished between 1-propanol and 2-propanol?

Ans 1: 1-propanol is primary alcohol while 2-propanol is a secondary alcohol.
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 # 8

Write the formulas of (a) Phosphorite (b) Chile saltpeter.

Ans 1: a) Phosphorite: Ca₃(PO₄)2
b) Chile saltpeter: NaNO₃

Question # 9

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 # 10

Give the classification of polymer?

Ans 1: IN 1929,W.H Carothers suggested a classification of the polymerization process into two depending upon the way the polymer are formed.
Addition Polymerization:It is free radical addition reaction which involves initiate,propagation and termination steps.For example polymerization of styrene.
Condensation polymerization: The polymerization results from the mutual reaction of two functional groups ,This reaction usually involves the removal of a water molecule or a methanol molecule,It take place at the both end of the growing chain.

Question # 11

What are steroids?

Ans 1: Steroids are naturally occurring lipids.Their parent nucleus has per hydri cyclopentanophenanthrene component which consists of three six members rings and one five membered ring these rings are joined or fused to each other an have a total of 17-C atoms,

Question # 12

What is lithosphere?

Ans 1: It consists of rigid rocky crust of earth and extends to the depth of 100 km,The mantle and core are the heavy interior of the earth,making up most of the earth mass,The 99.5% mass of the lithosphere is made of 11 elements,which are oxygen,Si,Al,Fe,Ca,Na,K,Mg And Ti,H₂and P.The elements in trace amount are C,Mn,S,Ba,CI,Cr,F,Zr,Ni,Sr and V,These elements mostly occur in the form off mineral.

Question # 13

Define coordination number.

Ans 1: The number of lone pair of electrons provided by the ligand to the central metal atom or ion is called the coordination number of the central metal atom or ion.

Question # 14

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 # 15

What is Benedict solution test?

Ans 1: 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 # 16

What is biochemical oxygen demand?

Ans 1: It is the capacity of an organic matter in natural water to consume oxygen within a period of five days.The value of BOD is the amount of oxygen consumed as a result of biological oxidation of dissolved organic matter is a sample.The oxidation reaction is catalyzed by microorganism which are already present in a natural water.It is measured experimentally by calculating the concentration of oxygen at the beginning and at the end of 5 days period in which a sealed water sample is maintained in dark at constant temperature either at 20 degree or 25 degree.

Question # 17

What are the common bleaching agent used in paper industry in Pakistan?

Ans 1: IN Pakistan ,bleaching is done with chlorine dioxide or sodium hypochlorite and hydrogen peroxide.

Question # 18

What is Tin Plating ?

Ans 1: The process of tin plating consists of dipping the clean sheet of iron in a bath of molten tin and then passing it through hot pair of roller.

Question # 19

How Portland cement is made?Why Gypsum is added in the cements?

Ans 1: Portland cement:Portland cement is made by strongly heating a finely powdered mixture of clay and limestone.The final product is known as clinker,is cooled and then ground into a very fine powder.
Ans 2: Addition of gypsum:During the grinding there is added about 2% of gypsum which prevents the cement from hardening too rapidly.The addition of gypsum increases the setting time of cement.

Question # 20

Detergents are threat to aquatic life.Explain.

Ans 1: Detergents are excessively used in industries and households as cleaning agents.The amount of disposed detergents in waste water is increasing day-by day,This waster water when discharge in river or sea,greatly affects the aquatic life.

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