Chemistry: Post your doubts here!

[daredevil]

can any 1 give explanations for the following mcqs:
m/j 2010 mcq 8 , 12:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s10_qp_12.pdf
o/n 2010 mcq 7 , 12, 13 ,18, 40 :
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
o/n 2011 mcq 30 :
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_12.pdf
m/j 2011 mcq 40 , 23 , 11:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s11_qp_12.pdf
Thanks in advance.

when u get the answers to the rest of the questions... plz tag me 2 bcuz they were mighty DIFICULT O__O x.x

 

[daredevil]

What do u get on heating:
MgCl2
MgCO3
Mg(NO3)2
Mg(OH)2

??

 

[littlecloud11]

At a total pressure of 1.0 atm dinitrogen tetraoxide is 50% dissociated at a temperature of 60 degree Celcius. according to the following equation:
N2O4-------------2NO2( reversible reaction)
what is the value of the equilibrium constant Kp, for this reaction at 60 degree Celcius?
A:1/3 atm
B:2/3 atm
C: 4/3 atm
D:2 atm
Common Guyz Someone reply please

Consider Initial moles of N2O4 as 1 and that of NO2 as zero.

Decomposition of one mole of N2O4 gives 2 moles of NO2
50% of N2O4 dissociates means that 1 moles of NO2 is formed. So total number of moles = 1.5

Partial pressure of N2O4 = 0.5/1.5 = 1/3
Partial pressure of NO2= 1/1.5 = 2/3

So Kp = (2/3)^2 divided by (1/3). So 4/3 is the answer.

 

[Ahmedraza73]

H2O(g)+C(s)________H2(g)+CO(g) deltaH= +131 kj/mol ( the reaction is reversible

When steam was passed over coke at 730 degree celcius,the following partial pressures were measured at equilibrium :
p(H2O)= 90 KPa
p(H2)= 183 KPa
(1) State what equilibrium partial pressure of carbon monoxide is and hence calculate the equilibrium constant.

Please Can anyone solve this?

 

[Ahmedraza73]

Consider Initial moles of N2O4 as 1 and that of NO2 as zero.

Decomposition of one mole of N2O4 gives 2 moles of NO2
50% of N2O4 dissociates means that 1 moles of NO2 is formed. So total number of moles = 1.5

Partial pressure of N2O4 = 0.5/1.5 = 1/3
Partial pressure of NO2= 1/1.5 = 2/3

So Kp = (2/3)^2 divided by (1/3). So 4/3 is the answer.

how u did the partial pressure step and why the 1.5 moles taken for both?

 

[littlecloud11]

What do u get on heating:
MgCl2
MgCO3
Mg(NO3)2
Mg(OH)2

??

The heating of course requires varying degrees of temperature, most of the reaction below does not take place with gentle heating.

MgCl2 -------> Mg + Cl2
MgCO3 ------> MgO + CO2
Mg(NO3)2 ------> Mg(NO2)2 + O2
Mg(OH)2 --------> MgO + H2O

 

[littlecloud11]

how u did the partial pressure step and why the 1.5 moles taken for both?

Initial moles of N2O4 was 1, 50% decomposed so .5 moles decomposed and .5 remained.
1 mole N2O4 gives 2 moles NO2, so .5 moles N2O4 gives 1 mole NO2.
total no of moles of gases at equilibrium is therefore .5+1 = 1.5

For partial pressure,the total pressure remains the same so you can use the mole ratio to calculate the partial pressure for each gas.
partial pressure= no of moles of a particular gas/ total no of moles of gas present.
Foe N2O4 this is .5/1.5 =1/3
for NO2 it is = 1/1.5 = 3/2

 

[ashiqbal]

What do u get on heating:
MgCl2
MgCO3
Mg(NO3)2
Mg(OH)2

??

The heating of course requires varying degrees of temperature, most of the reaction below does not take place with gentle heating.

MgCl2 -------> Mg + Cl2
MgCO3 ------> MgO + CO2
Mg(NO3)2 ------> Mg(NO2)2 + O2
Mg(OH)2 --------> MgO + H2O

only the second and third reactions take place on heating gently.
and the third reaction would go like this:
2 Mg(NO3)2 -----> 2 MgO+ 4 NO2 + O2

 

[sweetjinnah]

q 18:
is B the answer??
well u see it does vaporise because it it is a gas but when kept in a gas jar it does not stay above air.

atleast that's what i think...

ms stated mcq 18 correct answer D: gaseous bromine is purple.
seriously i dont get it.isnt gaseous bromine orange??

 

[sweetjinnah]

when u get the answers to the rest of the questions... plz tag me 2 bcuz they were mighty DIFICULT O__O x.x

so it is good for u and ur exam preparation . isn't it?

 

[daredevil]

ms stated mcq 18 correct answer D: gaseous bromine is purple.
seriously i dont get it.isnt gaseous bromine orange??

nahi... aqueous bromine vapours are brown but the gaseous bromine vapours are purple. just like pure iodine is dark purple while aqueous iodine we use in the labs is orange.

 

[daredevil]

so it is good for u and ur exam preparation . isn't it?

you bettt it waas!! it made freakin mind mince out of my head :O

 

[yubakkk]

 

[yubakkk]

llz answer my above question

 

[PhyZac]

llz answer my above question

8A ( Kindly, it would be more approriate to post this in math thread )
a) Friction=coefficient * normal contact
therefore, F = 0.25 * 94* 9.8 ( normal = mass x g )
=230.3 N
b) WD = Distance x force
= 230.3 x 5.2
=1197.56 J
c) PW = Speed x Force
=0.4 x 230.3
=92.12 W

 

[PhyZac]

llz answer my above question

8B
a)Mass = Mr in grams
Ca = 40.1 N=14 O=16
therefore Mr = 40.1 + (14 x 2) + (16 x 6)
=164.1 g
b) For every 1 mole of Ca(No3)2 there is 1 Ca2+
therefore, 0.05moles of Ca(NO3)2 gives 0.05 moles of Ca2+
number of particles = moles x Avogadro number
=0.05 x 6.022 x 10^23
=3.011 x 10^22
c)mole = mass / Mr
Mr of NaCl = 23 + 35.5 =58.5
therefore, 450 / 58.5 = 7.69 moles

 

[strangerss]

At a total pressure of 1.0 atm dinitrogen tetraoxide is 50% dissociated at a temperature of 60 degree Celcius. according to the following equation:
N2O4-------------2NO2( reversible reaction)
what is the value of the equilibrium constant Kp, for this reaction at 60 degree Celcius?
A:1/3 atm
B:2/3 atm
C: 4/3 atm
D:2 atm
Common Guyz Someone reply please

I hope you understand from me . If 50% of the nitrogen tetraoxide dissociate then 0.5 moles remain if it was one mole , if 0.5 remains from nitogen tetraoxide then 1 mole of the product is formed because the ratio of moles is 1:2 . so the pressure constant would be the partial pressure of the product which is 1/1.5 multiplied with one , raised to the power 2 because that's the number of moles from the equation. the answer is then divided into the partial pressure of the reactant which is 0.5/1.5 x 1 , thus the answer is 4/3 ... any one correct me if I'm wrong please

 

[Raiyan3]

Help me in Question no. 8 and 40
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf

 

[snowbrood]

nahi... aqueous bromine vapours are brown but the gaseous bromine vapours are purple. just like pure iodine is dark purple while aqueous iodine we use in the labs is orange.

i am afraid u are wrong aqueous bromine vapours or gaseous bromine vapours both are brown or orange... gaseous bromine is never purple but yeah aqueous iodine is orange

 

[daredevil]

i am afraid u are wrong aqueous bromine vapours or gaseous bromine vapours both are brown or orange... gaseous bromine is never purple but yeah aqueous iodine is orange

o right... but then can u plz answer that question sweetninjah asked?? and tag me in the answer too