12th Class Chemistry Short Questions Preparation for Pakistani Students

Question # 1

How lime and sand are used to make glass?

Ans 1: Water glass or soluble glass (Sodium Silicate) is prepared by fusing sodium carbonate(Lime) with pure sand (silica).This process is carried out in a furnace called reverberatory furnace.
Na₂CO₃+ SiO₂------>Na₂SiO₃+ CO₂

Question # 2

What is Zwitter ion?

Ans 1: The amino acid exist as dipolar ion called Zwitter ion,It has positive as well as negative ends within the same molecule.In the formation of Zwitter ion,the proton goes from the carboxylic group to amino group.

Question # 3

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 # 4

Give uses of iodine.

Ans 1: The major application of iodine are in pharmaceutical industry,It is used as disinfectants and germicides,Tincture of iodine and iodex are popular preparation of iodine.Diet with insufficient iodine ions leads to an enlargement of the thyroid,To ensure the present of iodine ion in the diet,sodium or potassium iodine is added to the common salt which is known as iodized salt.

Question # 5

Ethers are less reactive than alcohols.Justify

Ans 1: Ethers are comparatively inert substance.The reagents like ammonia,alkalies,dilute acids and metallic sodium have no action no ethers on cold state .Moreover they are not oxidized or reduced easily.
On the other hand alcohols can react with reagents due to C-O and O-H bonds.These can be oxidized and reduced ,Alcohols also undergo dehydration reaction.

Question # 6

Why do metals conduct electricity?

Ans 1: Metals conduct electricity:Metals conduct electricity because metals have loose(free) electrons in their outer most shell and ease of their movement in the solid lattice.

Question # 7

How phenol can be converted into benzene?

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

Question # 8

What is the difference glucose and fructose?

Ans 1: Glucose : Consists of aldehyde group and also called dextrose ,grape sugar or blood sugar ,occur naturally in both combines and free state ,Ib the free state it is present in most sweet fruits and in honey,Small quantity of glucose and also present in human blood and urine.
Fructose: consists of ketone group and is also found in combined and free states,It is used as a sweetening agent in confectionery and as substitute of cane sugar,

Question # 9

Brief about prilling of urea?

Ans 1: The molten urea is sprayed at the prilling tower by means of prilling bucket where it is cooled by the air rising upward,Molten droplets solidify into the form of prills,Urea prills thuis produced are either sent to the bagging section or to the bulk storage.

Question # 10

Why SO₃is dissolved in H₂SO₄and not in water?

Ans 1: SO₃is not directly dissolved in water,since absorption is incomplete and mist of SO₃and H₂SO₄fills the factory,which causes great causes great inconvenience the workers.Therefor,SO₃is absorbed in concentrated H₂SO₄and Oleum(H₂S₂O₇) formed can be converted to sulphuric acid of any strength by mixing adequate quantities of water.

Question # 11

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 # 12

Write the reaction of phenol with methanal.

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 # 13

Water has higher boiling point that ethanol.Explain.

Ans 1: Melting and boiling point of alcohol are higher than corresponding alkanes,Methyl alcohol and ethyl alcohol are liquids while methane and ethane are gases,This is also due to hydrogen bonding which is present in alcohols but absent in alkanes.

Question # 14

Discuss the trend of inoization energy in periodic table.

Ans 1: Trend of ionization energy in periodic table:In groups ionization energy decrease from top to bottom because size of atom and number of electrons causing the shielding effect also increases.
Ans 2: In period by moving from left to right the outer shell remains the same while the nuclear charge increase effectively that makes the removal of an electron difficult and hence the value of ionization energy increases.

Question # 15

How ozone layer in stratosphere is affected by chlorofluorocarbons?

Ans 1: Chlorofluorocarbons used as refrigerants in air conditioning and in aerosol spray are inert in the troposphere but slowly diffuse into stratosphere ,where they are subjected to ultraviolet radiation generating Ci free radicals which react with ozone and cause depletion.

Question # 16

Give reason that fluorine is gas ,iodine is solid?

Ans 1: Iodine molecule has larger size than fluorine,The intermolecular attraction is greater in the larger molecule having greater masses.Due to the larger size of iodine molecule the van der Waal forces are stronger than smaller size molecule of fluorine.

Question # 17

Define the preparation of methanol by reaction of Co and H₂?

Ans 1: First of all mixture of carbon monoxide and hydrogen is purified,It is compressed under a pressure of 200 atmospheres and taken into a reaction chamber by means of coiled pipers. These vapors are passed through a condenser to get methanol Unreacted gasses are recycled though compressor to reaction chamber.

Question # 18

How does HNO₃act as an oxidizing agent?

Ans 1: It acts as a strong oxidizing agent due to the ease with which it is decomposed.
2HNO_3(aq)---------->H₂O + 2NO₂(g) +[O]_(g)

Question # 19

What are amino acids?

Ans 1: Amino acids are organic compound containing both amino and carboxylic group.

Question # 20

Why is restricted rotation necessary to show the geometrical isomerism?

Ans 1: Two carbons atom joined by a single bond are capable of free rotation about it.However when two carbon atom are joined are joined by a double bond they can not rotate freely,As a result the relative position of the various groups attached to these carbons atoms get fixed and give rise to cis-temperature.