Chemistry Class 12 Essays

Chemistry Class 12 Essays Chemistry Class 12 Essay Chemistry Class 12 Essay HIGHER SECONDARY MODEL EXAMINATION HSE II Max. marks: 60 CHEMISTRY Time: 2. 45 hrs General instructions All questions are compulsory Cool-off time is 15 minutes 1] Defects modify the properties of crystals [4 marks] A] Give differences between Schottky and Frenkel defects [2. 0] B] On heating zinc oxide becomes yellow in colour. Why? [1. 0 ] C] Alkali metal halides on heating in presence of alkali metal produce characteristic colours. Give reason [1. 0] 2] Colligative properties depend on the number of solute particles in solution [4 arks] A] Give the name of colligative property suitable for the measurement of molar mass of starch[l . ] B] Give reasons for abnormal colligative properties [1. 0] C] Represent elevation in boiling point graphically [ 2. 0] 3] Cells are used for different purposes [4 marks] A] Differentiate between primary and secondary cells [ 1. 0] B] The voltage given by mercury cell is contant . Why ? [1. 0] C] What are fuel cells ? Give thei r two advantages . [2. 0] 4] Chemical kinetics deals with rates of chemical reactions [4 marks] A] Give two differences between order and molecularity of a chemical reaction [1. B] Draw a graphical representation to show the effect of a positive catalyst on the activation energy[l . 0] C] How rate of reaction increases with increase in temperature ? [1. 0] D] What is the half life of a first order reaction whose rate constant is 200 s-l? [1. 0] 5]Colloids are neterogeneous systems 13 marks] 2 A] Differentiate between Tyndall effect and Brownian movement [2. 0] B] State Hardy- Schulze rule for the coagulation of colloids [1. 0] 6]Metallurgy deals with the extraction of a metal from a suitable ore[3 marks] A] Which method of purification is epresented by the given equation? 1. 0] B] Differentiate between roasting and calcination [1. 0] C] All ores are minerals but all minerals are not ores . Justify the statement [1. 0] 7] Elements belonging from group 13 to group 18 are known as p-bl ock elements [5 marks] A] Draw the structures of phosphorous and sulphur molecules [1. 0] B] What are interhalogen compounds . Give example[l . 0] C] a. Account for the high viscous nature and boiling point of sulphuric acid[l . 0] b. Why are all the halogens usually coloured? [l . 0] D] Why are all bonds in PC15 molecule not equivalent? 1. ] 8]Elements from group 3 to group 12 are known as d block elements [4 marks] A] Explain the following observations: (i) Transition elements generally form coloured compounds. [l . 0] (it) Mercury is a liquid at room temperature [1. 0] B] Give the preparation of potassium permanganate from pyrolusite [2. 0] 9] Co- ordination compounds are addition compounds [4 marks] A] A coordination compound has the formula PtC14 . 3NH3. It does not liberate ammonia, but precipitates chloride ion as silver chloride. [2. 0] i. Write the IUPAC name and the structural formula of the compound. . What is the secondary valency of the compound in part (i)? B] Write do wn the II-PAC nomenclature of the following compounds: [2. 0] 3 i. [C0C12 (erl)2] S04 cr OH cr (NH3)5] C15 10] Halogen compounds reactive compounds [4 marks] A] (i) Why is it that haloalkanes are more reactive than haloarenes towards nucleophiles? [l . 0] (ii) Which one of the following reacts faster in an SNI reaction and why? B] Chloroform is kept in amber coloured bottles. Why? [1. 0] C] Differentiate the action of moist and dry silver oxide on bromomethane [1. 0] 1 1] Alcohols are important industrial solvents [4 marks] A] Which of the following alcohols give ketone on oxidation? [l . 0] B] What happens when dehydration of ethanol is carried at a higher temperature of 443 O] C] a] complete tne reaction b. Write all the possible structural isomers of the compound X [1. 0] 12] Aldehydes and ketones are carbonyl compounds [ 5marks] A] Giving reasons, arrange the following carbonyl compounds in the decreasing order of their reactivity in nucleophilic addition reactions. [2. O] B] Give two chemical tests to distinguish between CH3CHO and CH3COCH 3. . 0] C] Give a commercial method to obtain benzaldehyde from toluene. [l . 0] 4 D] Write the IUPAC name of the following compound. [l . 0] 13] Amines are derivatives of ammonia [3 marks ] A] Between ethylamine and ethyl alcohol, which has a higher boiling point and why? [ 1. 0] B]Giving reasons, arrange the given amines in the decreasing order of their basicity in the follow[ 2. 0] 14] Biomolecules are compl ex organic molecules [ 3 marks ] Match the following Glucose Amylose Reducing sugar Sucrose Aldohexose Zwitterion Starch Invert sugar ketohexose Fructose Glycine Linear polymer Amlnoac10 Denaturation Peptide linkage Proteins Sweetest sugar Non-reducing sugar 15] Polymers are macromolecules formed from monomers [ 3 marks ] a. What was the need for developing biodegradable polymers? [l . 0] b. What does PHBV stand for? Give its uses. [l . 0] c. Write the monomer units of Nylon 2-Nylon- 16] Chemistry plays an important role in our day to day life [ 3 marks ] a) State the function along with one example each of: [2. 0] (i) Antihistamines (it) Antioxidants (b) Give two differences between soaps and synthetic detergents [1. 0]