CBSE Class 12Th Chemistry
(1) Why do solids have a definite volume?
Ans:- The constituents particles in solids are bound to their mean positions by strong forces of attraction. The inter-particle distances remain unchanged even at increased or reduced pressure. Therefore, solids have a definite volume.
(2) What do you mean by vapour pressure? What happens to the vapour , when (I) Volatile happens to the vapour pressure, (ii) non-volatile solute is dissolve in solution ?.
Ans:- Vapour pressure-It is defined as the pressure exerted by a vapour in thermodynamic equilibrium with its condensed phased (solid or liquid) at a given temperature in a closed system.
(i) Volatile solute increases vapour pressure of solvent. (ii) Nonvolatile solute lowers vapour pressure of solvent
(3) How does the activation energy of a reaction affect the rate of reactions?
Ans:- The energy of activation of a reaction determines its rate. The reactions having lower energy of activation are fast, while the reactions having very high activation energy are extremely slow.
(4) Why does the reactivity of nitrogen differ from phosphorous ?
Ans:- The reactivity of Nitrogen differs from P due to (i) small size
(ii) high ionisation enthalpy and electronegativity
(iii) non-availability of d-orbitals with N.
(iv) Nitrogen has unique ability to form p-p multiple bonds with itself and with other elements having small size and higher electronegativity
(5) Any transition series contains only ten elements.why?
Ans:- There are only 10 members because in period left to right atomic number increases and hence after a certain number when D subshell is fully filled the electron has to go in S and P sub-shell hence it ends and P blocks. CBSE Class 12Th Chemistry
(6) What are the anionic detergents? How are they prepared ? Write their two main uses?
Ans:- The detergents which have negative charge on the surface active group in their molecules are called anionic deter- gentsSodium lauryl sulphate is a typical anionic detergentPreparation: Sodium lauryl sulphate is prepared by reacting aliphatic longchain alcohol.
(7) Chloroacetic acid is stronger than acetic acid, Why ? .
Ans:- Chloroacetic acid is stronger than acetic acid, because chlorine atom is an electron withdrawing group, which increases acidity of carboxilic acid. This effect makes more stable conjugate base. CBSE Class 12Th Chemistry
(8) H2O is liquid but H2S is gas, Why?
Ans:- In vapour state (~100 K) Sulphur partly exists as S_{2} molecules like O has two unpaired electrons in the anti-bonding a molecular orbital and exhibits paramagnetism.
(9) Define Point defect.
Ans:- The defects caused by a departure from the periodic arrangement of particles in the vicinity of an atom or group of atoms, are called point defects.
(10) What do you know chemical Adsorption ?
Ans:- Chemical adsorption-When the adsorbate is held to the surface of an adsorbent by forces nearly as strong as a chemical bond, the adsorption is called chemical Adsorption.
(11) Among HF,HCL,HBr and HI, which is the strongest reducing agent ?
Ans:- Among HF, HCI, HBr and HI; HI is the strongest reducing agent because the stability of hydrogen halides decreases on moving from HF to HI, the reducing property increases on moving down the graph. I has a very strong tendency to get oxidised to I_{2} So, It acts as strong reducing agent. CBSE Class 12Th Chemistry
(12) What are enzymes ?
Ans:- All biological reactions are catalysed by special
catalysts called enzymes. Thus enzymes are biological catalyst. enzyme facilitates a biochemical reaction by providing alternate lower activation energy pathways there by increasing the rate of the reaction. Chemically all enzymes are globular proteins. However same enzymes are also associated with same non-protein component called the co- factor for their activity. The enzymes differ from other type of catalyst in being highly specific and selective.
(13) What is semipermeable membrane ?
Ans:- Continuous sheets or films (natural or synthetic) which contain a network of submicroscopic holes or pores through which small solvent molecules (water etc.) can pass, but solute molecules of bigger size cannot pass are called semipermeable membrane.
(14) Define electrode and electrode potential.
Ans:- Electrode Solid electric conductor through which an electric current enters or leaves on electrolytic cell or the medium is called Electrode.
Electrode Potential-The electrical potential difference set up between the metal and its ions in the solution is I called electrode potential.
(15) What is emulsion? What are the different types? Give examples of each type.
Ans:- Liquid-liquid colloidal systems in which finely divided droplets of a liquid are dispersed into other liquid are called emulsions. These are formed by shaking the two immiscible liquids with each other.
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(16) What are artificial sweetening agents ? Give two examples.
Ans:- Sucrose, glucose etc. are natural sugars. They add to calorie intake. To cut down on the intake of calories many people use artifical sweeteners such as saccharine (ortho- Sulpho-benzimide) which is 550 times as sweet as sugar.
CBSE Class 12th Chemistry Sample Paper Solution
(mass to mass) with negligible calories. It is excreted from the body in urine unchanged. It is entirely inert and harmless when taken. It is of great value of diabetic persons and people who need to control intake to calories. Other example of artificial sweeteners are aspartame, sucrolose, alitame.
(17) Cyclohexamine is more basic than aniline.
Ans:- In cyclohexamine, the electron donating group is attached to sp 3d to hybridized cyclohexane ring while in case of aniline it is attached with S * P ^ 2 hybridized carbon containing benzene ringDue to more S-character in benzene ring, here becomes the de localization of л-electrons in the ring and further the N*H_{2} group donates more electron to the ring so that it reduces the +ve charge centers and stablizes the ring and moves it less acidic means basicity
new cyclohexamine, the lone pair of electron donating N*H_{2} group is not de localised over cyclohexane ring and is available for donation, which makes the compound more basic than aniline.
(18) What is a primary cell ? Give an example.
Ans:- The cell which produces electrical energy by virtue of chemical reaction within the cell is called a primary cell. The primary cells cannot be charged for repeated use.
Example: Dry cell, Daniell cell, Mercury cell.
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