Chemistry: Post your doubts here!

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

Q3,31,

 

[ZaqZainab]

Combustion of PbO is when it reacts with O2. This is not the combustion of Pb but PbO.
Formation of PbO is when Pb and O2 react to form PbO.

opps i mean A and D are the same thing right then?

 

[Suchal Riaz]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w13_qp_13.pdf

Q3,31,

H3 + means three hydrogen bonded to each other with a positive charge. so it has three protons. no neutrons. and 2 electrons are there is a positive charge on it.
L + is one lithium ion with one lithium-6 which has lost one electron. lithium has 3 protons. 6-3=3 neutrons. and has lost one electron so total 2 electrons.
now we have data. both contains three protons. both contain 2 electrons. but they do not contain same number of neutrons. (1) and (2) is correct. (3) is wrong. answer B

 

[Suchal Riaz]

opps i mean A and D are the same thing right then?

enthalpy change of combustion of lead means complete oxidation. until it oxidises to Pb3O4. that is same as formation of Pb3O4 not of PbO

 

[Suchal Riaz]

What factor decides that in finding enthalpy change of a reaction do we need the formation data or combustion data?!

enthalpy change of combustion means COMPLETE combustion. Carbon can form two products when burning: CO2 or CO.
enthalpy change of combustion of C is same as enthalpy change of formation of CO2 but not same as enthalpy change of formation of CO

 

[Suchal Riaz]

ahmed faraz

 

[crazytaylorfanXD]

Can someone please help me with a few questions
JUN 12 P13 ( Qs. 1 , 12 , 16 , 21 , 33 , 34 , 35 , 37)
i really need help urgently

 

[Suchal Riaz]

Can someone please help me with a few questions
JUN 12 P13 ( Qs. 1 , 12 , 16 , 21 , 33 , 34 , 35 , 37)
i really need help urgently

question number 1:
there is limited amount of nitrogen, hydrogen and ammonia.
at equilibrium N2 and H2 react to form NH3 and the reverse also happens. if you take away NH3 the backward reaction stops. so the concentration of reactants N2 and H2 will decrease. so the rate of forward reaction will occur.

 

[Suchal Riaz]

Can someone please help me with a few questions
JUN 12 P13 ( Qs. 1 , 12 , 16 , 21 , 33 , 34 , 35 , 37)
i really need help urgently

q12:
when heated CO2 was released so a metal carbonate decomposed.
effervescence indicate a metal carbonate was still present to react. so one metal carbonate must have decomposed and other could not decompose because it required higher temperature than bunsen burner to decompose. it means one is a Mg or Ca carbonate and other is a lower-in-group2-metal cabonate. only C fits the conditions.
q16
h2so4 will react with KCL to make HCL which will react with KI to make HI and KCL both are soluble and colorless
AGNO3 and Cl- will give a white ppt but it is soluble in even dilute NH3(aq) so a colorless solution again

 

[ZaqZainab]

enthalpy change of combustion of lead means complete oxidation. until it oxidises to Pb3O4. that is same as formation of Pb3O4 not of PbO

how do i deduce that? or should i just learn this?

 

[Suchal Riaz]

how do i deduce that? or should i just learn this?

no need to complicate the things. if you don't know anything you atleast know you need the enthalpy change which produces PbO but combustion of lead can give any lead oxide. we don't know which one but it can be PbO, PbO2 or whatever.

 

[GCE As and a level]

Guys
How much r u scoring ?? ........I am scoring in 20's

 

[Suchal Riaz]

Guys
How much r u scoring ?? ........I am scoring in 20's

i recently scored 40/40 in 31 minutes(physics paper) and then 39/40 in 41 minutes(chemistry)
when i started doing papers i was at 27. the marks increased with practice till maximum of 36/40. with more and more practice and if only i am totally awake when doing paper i score 38+ otherwise 37 is an average.

 

[kitkat <3 :P]

i recently scored 40/40 in 31 minutes(physics paper) and then 39/40 in 41 minutes(chemistry)
when i started doing papers i was at 27. the marks increased with practice till maximum of 36/40. with more and more practice and if only i am totally awake when doing paper i score 38+ otherwise 37 is an average.

*FAINTS* *WAKES UP* *READ THE POST AGAIN* *DIES* -_-

 

[Suchal Riaz]

*FAINTS* *WAKES UP* *READ THE POST AGAIN* *DIES* -_-

i started from 27/40. if you practice you can also reach 40/40. it was supposed to encourage you not to befuddle you.

 

[AbbbbY]

i recently scored 40/40 in 31 minutes(physics paper) and then 39/40 in 41 minutes(chemistry)
when i started doing papers i was at 27. the marks increased with practice till maximum of 36/40. with more and more practice and if only i am totally awake when doing paper i score 38+ otherwise 37 is an average.

Funny. I was at 36+ before my exams began. Now I'm at 28-30. Stupid 20 day gap that I wasted.

 

[kitkat <3 :P]

i started from 27/40. if you practice you can also reach 40/40. it was supposed to encourage you not to befuddle you.

.........
2 days

 

[GCE As and a level]

i recently scored 40/40 in 31 minutes(physics paper) and then 39/40 in 41 minutes(chemistry)
when i started doing papers i was at 27. the marks increased with practice till maximum of 36/40. with more and more practice and if only i am totally awake when doing paper i score 38+ otherwise 37 is an average.

So do u mean that i will fail and that i am a loser
JOKING..I know ur trying to give me a push
THNX
I solved many papers but still i am ranging in 20's
BTW i am only talking CHEMISTRY
BEST OF LUCK BRO

 

[Suchal Riaz]

Funny. I was at 36+ before my exams began. Now I'm at 28-30. Stupid 20 day gap that I wasted.

i was at 38 too when i did 2000-2006 papers for my mocks. and with gap i got to 27 because i just forgot studies and started programming.

 

[GCE As and a level]

Funny. I was at 36+ before my exams began. Now I'm at 28-30. Stupid 20 day gap that I wasted.

WE** Not I