CBSE Class 12 Chemistry Solved Question Paper: 2017

Get completely Solved CBSE Class 12th Chemistry 2017 board exam paper in PDF format. Download link is available at the end of this article. This paper was held on 25th March 2017.

With this solved paper, students can easily understand the level of questions which can be asked in coming CBSE Class 12th Chemistry board exam 2018.

Analysis & Review of CBSE Class 12 Chemistry Board Exam 2017

If you want to learn about the latest Examination Pattern of CBSE Class 12 Chemistry board exam 2018 then please go through latest CBSE 12^th Chemistry Sample Paper. This paper is recently released by CBSE.

CBSE Class 12 Chemistry Sample Paper: 2018

Some randomly selected questions from solved paper of 12^th Chemistry 2017 board exam are given below:

Question:

What is the effect of adding a catalyst on

(a) Activation energy (E_a), and

(b) Gibbs energy (ΔG) of a reaction?

Solution:

(a) Activation energy decreases as catalyst provide a new reaction path in which a lower activation is offered.

(b) There will be no effect of Gibbs free energy, as for catalyzed & uncatalyzed reaction, the equilibrium constant is not affected and equilibrium constant is a function of Gibbs free energy.

CBSE Class 12 Chemistry Syllabus 2017 – 2018

Question:

What type of colloid is formed when a liquid is dispersed in a solid? Give an example.

Solution:

Gel.

Example:  Cheese.

Question:

Write the name of the cell which is generally used in hearing aids. Write the reactions taking place at the anode and the cathode of this cell.

Solution:

Mercury cell are used.

Anode:

Zn (Hg) + 2 OH ^̶ → ZnO (s) + H₂O + 2e ^̶

Cathode:

HgO + H₂O + 2e ^̶ → Hg (l) + 2 OH ^̶

Question:

Using IUPAC norms write the formulae for the following :

(a) Sodium dicyanidoaurate (I)

(b) Tetraamminechloridonitrito-N-platinum (IV) sulphate

Solution:

(a) Sodium dicyanidoaurate (I):  Na[Au(CN)₂]

(b) TetraamminechloridonitritoN-platinum (IV) sulphate: [Pt(NH₃)₄Cl(NO₂)](SO₄)

Question:

(a) What type of isomerism is shown by the complex [Co(NH₃)₅ (SCN)]²⁺ ?

(b) Why is [NiCl₄]^{2 ̶}  paramagnetic while [Ni(CN)₄] ^{2 ̶}   is diamagnetic ? (Atomic number of Ni = 28)

(c) Why are low spin tetrahedral complexes rarely observed?

Solution:

(a) Linkage isomerism

(b) [NiCl₄]^{2 ̶}  paramagnetic while [Ni(CN)₄] ^{2 ̶}   is diamagnetic because in [NiCl4]^2-, due to the presence of Cl^- , a weak field ligand no pairing occurs whereas in [Ni(CN)4]^2- , CN^- is a strong field ligand and pairing takes place.

(c) Low spin tetrahedral complexes are rarely observed because the orbital splitting energies are not sufficiently large for forcing pairing. Due to which electron always goes to higher states avoiding pairing.

Question:

Write one difference in each of the following:

(a) Multimolecular colloid and Associated colloid

(b) Coagulation and Peptization

(c) Homogeneous catalysis and Heterogeneous catalysis

Solution:

(a)

Multimolecular Colloid	Associated Colloid
It is Aggregation of large number of small atoms or molecules.	It is aggregation of large number of ions in concentrated solutions.

(b)

Coagulation	Peptization
Settling down of colloidal particles.	Conversion of precipitate into colloidal sol by adding small amount of electrolyte.

(c)

Homogenous catalysis	Heterogeneous catalysis
Reactants and catalyst are in same phase	Reactants and catalyst are in different phases.

Question:

Write the principle of the following:

(a) Zone refining

(b) Froth floatation process

(c) Chromatography

Solution:

(a) Zone Refining – It is based on the principal that the impurities are more soluble in molten state than in the solid state. It is used to obtain metal of high purity.

(b) Froth floatation process – 

In this process, mineral particles are wetted by oils forming froth while gangue particles are wetted by water and settle down. A rotating paddle agitates the mixture and draws air in it. As a result froth is formed which carries the mineral particles. It is used to concentrate sulphide ore.

(c) Chromatography – It is based on the principle that different components of a mixture are differently adsorbed on an adsorbent. After which the adsorbed component are removed by using suitable solvents.

Question:

Give reasons for the following:

(a) Red phosphorus is less reactive than white phosphorus.

(b) Electron gain enthalpies of halogens are largely negative.

(c) N₂O₅ is more acidic than N₂O₃.

Solution:

(a)

Red phosphorous being polymeric is less reactive than white phosphorous which has discrete tetrahedral structure. White phosphorus posses angle strain in the P₄ molecule where the angle are only 60^o.

(b)

Electron gain enthalpies of halogens are largely negative because they readily accept an electron to attain noble gas configuration.

(c)

N₂O₅ is more acidic then N₂O₃ because in N₂O₅ the N is in +5 oxidation state whereas in N₂O₃ it is in +3 oxidation state. Higher the oxidation state of central atom in a given oxide, higher will be acidic character.

Question:

After watching a programme on TV about the presence of carcinogens (cancer causing agents) Potassium bromate and Potassium iodate in bread and other bakery products, Rupali a Class XII student decided to make others aware about the adverse effects of these carcinogens in foods. She consulted the school principal and requested him to instruct the canteen contractor to stop selling sandwiches, pizzas, burgers and other bakery products to the students. The principal took an immediate action and instructed the canteen contractor to replace the bakery products with some protein and vitamin rich food like fruits, salads, sprouts, etc. The decision was welcomed by the parents and the students. After reading the above passage, answer the following questions:

(a) What are the values (at least two) displayed by Rupali ?

(b) Which polysaccharide component of carbohydrates is commonly present in bread?

(c) Write the two types of secondary structures of proteins.

(d) Give two examples of water soluble vitamins.

Solution:

(a) Rupali is concerned, caring and socially alert.

(b) The polysaccharide component of carbohydrates commonly present in bread is Starch.

(c) α -Helix and β-pleated sheets

(d) Vitamin B and Vitamin C.

Question:

(a) Account for the following:

(i) Transition metals show variable oxidation states.

(ii) Zn, Cd and Hg are soft metals. 

(iii) E° value for the Mn^3+/Mn²⁺ couple is highly positive (+ 1·57 V) as compared to Cr³⁺/Cr²⁺.

(b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements.

Solution:

(a)

(i)

Transition metals show variable oxidation states due to the availability of partially filled d-orbitals / comparable energies of ns and (n-1) d orbitals.

(ii)

Group 12 elements (Zn, Cd, Hg) have Completely filled d-orbitals and there is absence of unpaired d electrons cause weak metallic bonding due to which they are soft.

(iii)

Eº value for the Mn⁺³/Mn⁺² is high because Mn²⁺ has d⁵ as a stable configuration whereas Cr³⁺ is more stable due to stable t³_2g.

Similarity:

• Both series elements are stable in +3 oxidation state.

• Both series elements show contraction.

Difference:

• Actinoids are radioactive whereas Lanthanoids are not radioactive.

• Actinoids show wide range of oxidation states but lanthanoids don’t show wide range of oxidation states.

Download CBSE Solved Paper for Class 12 Chemistry 2017 Board Exam in PDF format