chemistry_9701/1_ppr1_jun04 & nov 04!!

[tweez11]

PLEASE can someone explain me the following questions..wud be thankful!
CHEM PPR1
JUNE 04
Q8,9,16(why not C?),18,28!

NOV 04
Q3,10,12(why not A?),18,23,25,,33(why not A..activation energy dznt get affected by temp or conc?)
,37,38,39!!
plz fully explaination is needed..urgently!!

 

[soumayya]

J 04 No.8
3FeO(s) + 2Al (s) --->
3Fe(s) + Al 2O3(s)

u have to draw a hess cycle with the arrows pointing towards FeO and Al2O3
don't 4get to multiply the enthalpy change of formation of FeO by 3 since there are 3 moles in the equation
reverse the sign for enthalpy change of formation of FeO because u would b going against the direction of the arrow
enthalpy change of rection = 3(266) - 1676 = -878 KJ/mol

 

[soumayya]

J 04 No. 9
It cannot be ethanoic acid because it is a weak acid and will not produce the same amt of H+ in solution as HCl
Sodium hydroxide is an alkali, so will produce OH- in solution, not H+
Sulphuric acid is a dibasic acid producing twice as much H+ in solution compared to HCl
so...HNO3 is the answer...it is a strong monobasic acid, just lyk HCl

 

[soumayya]

J 04 No. 16
Li2+ cation has high polarising effect on the large carbonate anion(like Mg2+), so distorting its electon cloud system....hence LiCO3(like MgCO3) is partly covalent and decomposes at low temperatures...
magnesium does react readily with oxygen..

 

[soumayya]

J 04 No.18
NaCl + H2O ---> NaOH + 1/2 Cl2 + 1/2 H2
58.5 g (1 mole) of NaCl gives 35.5 g (0.5 mole) of Cl2 , 1 g (0.5 mole) of H2 and 40 g (1 mole) of NaOH
58.5 kg of NaCl gives 35.5 kg of Cl2, 1 kg of H2 and 40 kg of NaOH

 

[soumayya]

J 04 No. 28
u just have to put OH and H as u break the C double bond C
only compound D gives a tertiary alcohol (which is generally unreactive towards mild oxidising agent like K2Cr2O7)

 

[soumayya]

N 04 No. 3
10 cm3 of CH3SH will produce 20 cm3 of gases (10 cm3 of CO2 + 10 cm3 of SO2...not counting H2O since it is liquid at room temperature)
only 30 cm3 of O2 will react, so there will be 30 cm3 of O2 remaining
Total volume of gases= 20 + 30 = 50

 

[soumayya]

u've got an explanation for the other numbers...????
btw...u understood my explanations..???