Chemistry: 2006:CBSE:[All India]:Set I
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Q1
Name the non-stoichiometric point defect responsible for colour in alkali halides. Marks:1View AnswerAnswer:
F-centers
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Q2
Define ‘mole fraction’ of a substance in a solution. Marks:1View AnswerAnswer:
Mole fraction is defined as the number of moles of a component divided by total number of moles of all components present in the solution.Sum of mole fractions of all the components of the solution is always 1. -
Q3
A reaction is 50% complete in 2 hours and 75% complete in 4 hours. What is the order of the reaction? Marks:1View AnswerAnswer:
First order. -
Q4
Write the IUPAC name of CH3COCH2COCH3. Marks:1View AnswerAnswer:
The IUPAC name of the compound is Pent-2,4-dione. -
Q5
Give a chemical test to distinguish between a primary and a secondary amine. Marks:1View AnswerAnswer:
Carbylamine Test: A primary amine on heating with chloroform and alcoholic KOH gives carbylamine which has foul smell whereas a secondary amine does not respond to this test. -
Q6
Account for the following: (i) N2 has higher bond dissociation energy than NO. (1) (ii) N2 and CO both have same bond order but CO is more reactive than N2. (1) Marks:2View AnswerAnswer:
(i) Molecular orbital theory suggest that Bond order of N2 is 3 and that of NO is 2.5.As we know that higher the bond order,lesser is the bondlength. It means N2 has higher bond dissociation energy than that of NO. (ii) Due to significant electronegativity difference in CO, it is polar in nature whereas N2 is non-polar because of having zero electronegativity difference within molecule.That is why CO is more reactive than N2. -
Q7
At absolute zero, an exothermic reaction is always spontaneous but at temperatures above absolute zero, we have to consider both enthalpy and entropy before we can predict spontaneity. Why? out of syllabus
Marks:2View AnswerAnswer:
G = H – TS
The process is spontaneous only when 
G is -ve
At absolute zero, T = 0. 
TS is zero and thus G = H
As we know that H is –ve for any exothermic reaction.
It means at absolute temperature( T = 0),G is always -ve for exothermic reactions (enthalpy driven process).
At temperature above absolute zero,
TS is no more zero apart this enthalpy change start playing its role . Hence, we have to consider both H and TS to predict spontaneity of the reaction. -
Q8
Write the chemical equations involved in the preparation of the following:
i) XeF4
ii) H3PO3 Marks:2View AnswerAnswer:
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Q9
Why is the +2 oxidation state of manganese quite stable, while the same is not true for iron? [Mn = 25, Fe = 26] Marks:2View AnswerAnswer:
Electronic configurations: Mn = [Ar]3d54s2 and Fe = [Ar]3d64s2 . For +2 oxidation state outer electronic configuration of Mn2+ and Fe2+ are 3d5 and 3d6, respectively. 3d5 is more stable than 3d6 because half-filled orbitals are more stable than partly filled orbitals. Hence, Mn+2 is quite stable. -
Q10
Give reasons for the following:
a.Ortho-nitrophenol is more acidic than ortho-methoxyphenol. (1)
b.Why do sopes not work in hard water?(1) Marks:2View AnswerAnswer:
(a) As we know that proton donors are acids and the substance which gives proton easily, shows more acidic behaviour.Due to -M effect of nitro group, the lone pair of electrons in –OH group is pulled and H+ ion is easily released. Contrary to this methoxy group being electron releasing in nature, increases –ve charge on –OH group and H+ ion is not removed easily. Hence, ortho-nitrophenol is more acidic. (b) Since hard water contains Ca2+ and Mg2+ ions and these ions form insoluble calcium and magnesium soaps and seperate as scum in water.
In fact these stick onto the fibre of the cloth as gummy precipitate and create hinderance to good washing.
