Chemistry Class 12

Topics: Reaction rate, Chemistry, Chemical reaction Pages: 5 (737 words) Published: December 10, 2013


Max.marks: 60


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


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 marks] A] Give the name of colligative property suitable for the measurement of molar mass of starch[1.0]
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 their 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 [1.0] B] Draw a graphical representation to show the effect of a positive catalyst on the activation energy[1.0]

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−1? [1.0] 5]Colloids are heterogeneous systems [3 marks]

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 represented 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-block elements [5 marks]
A] Draw the structures of phosphorous and sulphur molecules [1.0] B] What are interhalogen compounds . Give example[1.0]
C] a. Account for the high viscous nature and boiling point of sulphuric acid[1.0] b. Why are all the halogens usually coloured?[1.0]
D] Why are all bonds in PCl5 molecule not equivalent? [1.0]
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.[1.0] (ii) 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 PtCl4 . 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. ii. What is the secondary valency of the compound in part (i)? B] Write down the IUPAC nomenclature of the following compounds: [2.0]

i. [CoCl2 (en)2] SO4
ii.[(NH 3)5 Cr − OH − Cr (NH3)5] Cl5
10] Halogen compounds reactive compounds [4 marks]
A] (i) Why is it that haloalkanes are more reactive than haloarenes towards nucleophiles?[1.0] (ii) Which one of the following reacts faster in an SN1 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] 11] Alcohols are important industrial solvents [4 marks]
A] Which of the following alcohols give ketone on oxidation?[1.0]

B] What happens when dehydration of ethanol is carried at a higher temperature of 443 K?[1.0] C]

a] Complete the reaction [1.0]

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...
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