HBSE Class 12 Chemistry Question Paper 2019 Answer Key
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Q1.(i) What is tincture of iodine ?
(A) 0.2 to 0.4 ppm aqueous solution of chlorine
(B) 2-3% aqueous solution of CH3COOH
(C) 2-3% solution of iodine in alcoholwater
(D) None of the above
Ans. (C) 2-3% solution of iodine in alcoholwater
(ii) What is hybridization of Ni in [NiCl4]²- ?
(A) sp³d
(B) dsp²
(C) sp³d²
(D) sp³
Ans. (D) sp³
(iii) Which of the following organic compounds are formed by Wurtz reaction ?
(A) Alcohols
(B) Hydrocarbons
(C) Haloalkanes
(D) Haloarenes
Ans. (B) Hydrocarbons
(iv) Glycogen is an example of :
(A) Polysaccharide
(B) Disaccharide
(C) Monosaccharide
(D) Protein
Ans. (A) Polysaccharide
(v) According to Hardy-Schulze rule, which of the following has highest flocculating power ?
(A) Al³+
(B) Ba²+
(C) Na+
(D) None of the above
Ans. (A) Al³+
(vi) What type of stoichiometric defect is shown by ZnS ?
Ans. Frenkel Defect
(vii) Give structure of monomer unit of Nylon-6.
Ans.
(viii) What do you mean by Peptide linkage ?
Ans. It is linkage (or bond) by which α-amino acids are connected to each other in a protein.
(ix) Define Azeotrope mixture.
Ans. Azeotropes are binary mixtures having same composition in liquid and vapour phase and boil at constant temperature.
(x) Write the Nernst equation for following cell :
Sn(s) | Sn²+ || H+ | H2 (g)(1bar) | Pt(s)
Ans. E = E⁰ – 0.059/2 log [Sn²+]/[H+]²
(xi) Identify the reaction order from the following rate constant :
k = 3.5 × 10-⁵ L mol-¹ s-¹
Ans. Second Order
(xii) Write the reaction of Cl2 with water.
Ans. 2Cl2 + 2H2O → 4HCl + O2
Or
Cl2 + H2O → 2HCl + [O]
(xiii) Write IUPAC name of (p) O2N–C6H4–OCH3
Ans. 4-Nitroanisole
(xiv) Draw structure of cyclopropanone oxime.
Ans. ∆=NOH
Q2. If the density of some lake water is 1.25 g ml-¹ and contains 92 g of Na+ ions per Kg of water, calculate the molality of Na+ ions in the lake.
Ans. Mass of Na+ ions = 92 g
Moles of Na+ ions = 92/23 = 4
Mass of water = 1 Kg
Molality = 4/1 = 4 m
Q3. If a current of 0.5 ampere flows through a metallic wire for 2 hours, then how many electrons would flow through the wire ?
Ans. Coulombs of electrons = current × time = 0.5A × 2 × 60 × 60s = 3600 C
Now, 96500 C is equivalent to = 6.022 × 10²³ electrons
3600 C is equivalent to = (6.022×10²³ ÷ 96500) × 3600 = 2.246 × 10²² electrons
Q4. Differentiate between cationic and anionic detergents giving suitable examples.
Ans. Cationic detergents– These are quaternary ammonium salt of amines with acetates, chlorides or bromides. e.g. cetyltrimethyl ammonium bromide.
Anionic detergents– Anionic detergents are sod. salt of sulphonated long chain hydrocarbons or alcohols. e.g. Sod. laurylsulphate.
Q5. Explain the term copolymerization and give two examples.
Ans. Process in which two or more monomer combine to form a polymer. e.g.
(i) 1, 3-Butadiene and styrene
(ii) 1, 3-Butadiene and acrylonitrile
Q6. What do you mean by denaturation of a protein ? How does it affect properties of protein ?
Ans. When a protein in its native form is subjected to physical or chemical change, the hydrogen bonds are disturbed. This is called Denaturation of a protein.
Denaturation changes physical and biological properties but chemical properties remains the same.
Q7. It is safe to inject solutions isotonic with blood plasma intravenously. Explain.
Ans. During intravenous injections, the conc. of the solution to be injected should be comparable to blood plasma. If the solution is more conc. then water will flow out of cell & they would shrink. If the solution is less conc. then water will flow into cell & they would burst.
Q8. While giving labelled diagram of dry cell write reactions taking place at cathode and anode.
Ans.
Anode : Zn(s) → Zn²+ + 2e-
Cathode : MnO2 + NH4+ + e- → MnO(OH) + NH3
Q9. Why does nitrogen show catenation properties less than phosphorus ?
Ans. Single N-N bond is weaker than single P-P bond because of high inter electronic repulsion of the non bonding electrons, owing to the small bond length. As a result the catenation tendency is weaker in Nitrogen.
Q10. Although amino group is o- and p- directing in aromatic electrophilic substitution reactions, aniline on nitration gives a substantial amount of m-nitroaniline. Give reason.
Ans. This is because in strongly acidic medium (conc. HNO3 + H2SO4), the aniline is pronated to form anilinium ion which is meta directing. Thus in addition to 0- & p- derivatives, significant amount of m-derivative is also formed.
Q11. Write a short note on Hofmann’s bromamide reaction.
Ans. This is a method for preparation of 1° amines in which an amide is treated with bromine in an aq. or alc. solution of NaOH.
R–C=O–NH2 + Br2 + 4NaOH → R–NH2 + Na2CO3 + 2NaBr + 2H2O
Q12.(a) What is meant by Hydroboration-oxidation reaction ? Illustrate it with an example.
Ans. Diborane (BH3)2 reacts with alkene to give trialkyl boranes as addition product. This is oxidized to alcohol by H2O2 in the presence of aq. NaOH.