Physics, Chemistry and Biology: Post your doubts here!

[Dashexdan]

My last 2 doubts are still unanswered.

1c(ii)

 

[chaotic]

1c(ii)

Broken link.

 

[Dashexdan]

Broken link.

hmm..srry

 

[Dashexdan]

Broken link.

6b(ii)
http://www.webchem.net/notes/chemical_bonding/ionic_bonding.htm

 

[AAnsarii]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w11_qp_32.pdf

Also,
4a (i)
4b (i)
5c
5d
6c
7c

Please need help, I'm bad in chemistry, also still waiting for answer about my past doubt.

4 (a)(i)Refer 2 d periodic tbl 4 d valencies-- Sc3+, F-
so there will b 3 F to make d compound:: ScF3 Draw a circle of Sc3+, no e- around it. draw three F atoms, 7 o's and 1 x around each.
(b)(i) agan valency in PT... Si is 4, O is 2.. Cross them, Si2O4... thus, draw 4 O around evy Si n 2 Si around evy O
5(c) methanol, 1 C atom... CH3OH
C has 4 valency electrons, draw dat
around d C, 3 H n 1 O....
beside d O, one more H (4m OH) Refer 2 d file uploaded
(d) when propanol is oxidised, u get propanoic acid
C3H5COOH
evy C must have 4 bonds, O 2 bonds, H ONLY 1 bond
refer 2 d file uploaded
(ii) u want it 2 b oxidised, leave it open in air (dat contains Oxygen!) n u want it by fermentation, so use microbes/bacteria, etc.
6(c) lo! behold! Stoichiometry....

moles of BaSO4: 1 mol has a mass of 233g, n in reality, 1.398 g r 4med.. so x will give u 1.398g. unitery method--233/1.398 = 0.006
moles fo MgSO4.xH2O: refer 2 d eqn....1 molecule gives 1 molecule, so 0.006 will (sensible, hmm..) give u 0.006, rite?
they've given u d mass of hydrated mg sulfate..1.476....so again 0.006 gives 1.476, so 1 will give u 1.476/0.006 = 246
the anhydrous thing is 120 g so 4m 246, how much is water? i think 126?
Moles = mass/Mr = 126/(16+2(1)) = 126/18 = 7
hp u got it....
7(c) 0.026 mols of Pb + 0.104 mols of C2H5 = ur prod
so 1 mol of Pb(refer 2 d qn, only 1 atom or whatever is there) will use 0.104/0.026 C2H5 = 4......thus n=4


hope u got it..sorry 4 being so bad at xplaining

all d best, n u'll do good, wid the Lord's Help, 4 its only He who CAN help.....

 

[chaotic]

6b(ii)
http://www.webchem.net/notes/chemical_bonding/ionic_bonding.htm

Thanks man.

4 (a)(i)Refer 2 d periodic tbl 4 d valencies-- Sc3+, F-
so there will b 3 F to make d compound:: ScF3 Draw a circle of Sc3+, no e- around it. draw three F atoms, 7 o's and 1 x around each.
(b)(i) agan valency in PT... Si is 4, O is 2.. Cross them, Si2O4... thus, draw 4 O around evy Si n 2 Si around evy O
5(c) methanol, 1 C atom... CH3OH
C has 4 valency electrons, draw dat
around d C, 3 H n 1 O....
beside d O, one more H (4m OH) Refer 2 d file uploaded
(d) when propanol is oxidised, u get propanoic acid
C3H5COOH
evy C must have 4 bonds, O 2 bonds, H ONLY 1 bond
H H O
| | ||
H--C---C---C--O--H
| |
H H
(ii) u want it 2 b oxidised, leave it open in air (dat contains Oxygen!) n u want it by fermentation, so use microbes/bacteria, etc.
6(c) lo! behold! Stoichiometry....

moles of BaSO4: 1 mol has a mass of 233g, n in reality, 1.398 g r 4med.. so x will give u 1.398g. unitery method--233/1.398 = 0.006
moles fo MgSO4.xH2O: refer 2 d eqn....1 molecule gives 1 molecule, so 0.006 will (sensible, hmm..) give u 0.006, rite?
they've given u d mass of hydrated mg sulfate..1.476....so again 0.006 gives 1.476, so 1 will give u 1.476/0.006 = 246
the anhydrous thing is 120 g so 4m 246, how much is water? i think 126?
Moles = mass/Mr = 126/(16+2(1)) = 126/18 = 7
hp u got it....
7(c) 0.026 mols of Pb + 0.104 mols of C2H5 = ur prod
so 1 mol of Pb(refer 2 d qn, only 1 atom or whatever is there) will use 0.104/0.026 C2H5 = 4......thus n=4


hope u got it..sorry 4 being so bad at xplaining

all d best, n u'll do good, wid the Lord's Help, 4 its only He who CAN help.....

Thanks for the hard work, you putted effort in that .

 

[kainat husain]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w11_qp_32.pdf

Also,
4a (i)
4b (i)
5c
5d
6c
7c

Please need help, I'm bad in chemistry, also still waiting for answer about my past doubt.

6c- the num of baso4 formed is 0.006 cux
Mass of barium sulfate formed = 1.398 g
SO n=m/mr so 1.398/233 = 0.006
The number of moles of MgSO4.xH2O = 0.006 because both are 1 ;/ i dunno how to explain :/
The mass of one mole of MgSO4.xH2O = as we know Mass of hydrated magnesium sulfate = 1.476 g
so, n= m/mr......0.006= 1.476/mr
so mr= 246g
The mass of xH2O in one mole of MgSO4.xH2O = as we know The mass of one mole of MgSO4 = 120g
so, 246-120= 126g
x= 7 because 126/18
and we got 18 by H*2+16
so n= m/mr
q7c u jus have to divide 0.104/0.026... i dunno y but i got the answer by checkin the valency from periodic tabel
the answer for others are attached except 5c i dunno tht one
EDIT- the third drawing is wrong it has to be alcohal IGNORE IT

 

[chaotic]

6b(ii)
http://www.webchem.net/notes/chemical_bonding/ionic_bonding.htm

Can you explain how you did this? I got some idea, but still need elaboration.

Thanks in advance.

 

[AAnsarii]

locating agent in chromatography shows u d clr rite?

 

[thats_me]

locating agent in chromatography shows u d clr rite?

Yes but depends on the one u use with uv light u get black spot n with resorcinol and ninhydrin coloured

 

[chaotic]

6c- the num of baso4 formed is 0.006 cux
Mass of barium sulfate formed = 1.398 g
SO n=m/mr so 1.398/233 = 0.006
The number of moles of MgSO4.xH2O = 0.006 because both are 1 ;/ i dunno how to explain :/
The mass of one mole of MgSO4.xH2O = as we know Mass of hydrated magnesium sulfate = 1.476 g
so, n= m/mr......0.006= 1.476/mr
so mr= 246g
The mass of xH2O in one mole of MgSO4.xH2O = as we know The mass of one mole of MgSO4 = 120g
so, 246-120= 126g
x= 7 because 126/18
and we got 18 by H*2+16
so n= m/mr
q7c u jus have to divide 0.104/0.026... i dunno y but i got the answer by checkin the valency from periodic tabel
the answer for others are attached except 5c i dunno tht one
EDIT- the third drawing is wrong it has to be alcohal IGNORE IT

Thank you, but in The number of moles of MgSO4.xH2O and mass of one mole of MgSO4.xH2O, is there something tricky? don't you need the mass of one mole to find the number? but the question asks to find the number of moles first and not the mass of one mole.

 

[mahmouds]

physics doubts !!!!!
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w07_qp_6.pdf
in question 4 (b), I used a protractor and the angle must be 90 degree. is t rejected or can work.
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_s08_qp_6.pdf
question 1 (b). I need more than one possible method if you please.
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Physics (0625)/0625_w09_qp_6.pdf
question 4 (b) (iii), which need a drawing for measuring thickness of a converging lens.
I had posted before but no one had replied, so plz it is urgent !!!!!!

 

[AAnsarii]

http://www.xtremepapers.com/papers/CIE/Cambridge%20IGCSE/Chemistry%20(0620)/0620_w11_qp_33.pdf
6 (b)(i)
Plz xplain all d things dat affect equilibrium..

same ppr, in org chem, u have 2 do d repeat units when drawing polymers...how do u do dat??

 

[Dashexdan]

Can you explain how you did this? I got some idea, but still need elaboration.

Thanks in advance.

lithium oxide has the electronic configuration of 2,1 so it has 1 electron in its outer shell that it can loose or give some other non metal such as oxygen
and oxygen has config. of 2,6 so to complete oxygens outer shell we need 2 more electrons and to cmplete lithiums outer shell we need to remove 1 electron.
thus if we use to li and take one electron from each of them and give it to oxygen so both of the elements outer shell will be complete. thus having formula of Li2O

 

[thats_me]

http://www.xtremepapers.com/papers/CIE/Cambridge%20IGCSE/Chemistry%20(0620)/0620_w11_qp_33.pdf
6 (b)(i)
Plz xplain all d things dat affect equilibrium..

Increase in temp causes equilibrium to shift to the endothermic side
increase in pressure causes the equilibrium to shift to the sides with fewer moles

 

[AAnsarii]

Increase in temp causes equilibrium to shift to the endothermic side
increase in pressure causes the equilibrium to shift to the sides with fewer moles

how do u noe dat its endo or exo? in d qn, its 200 degree C, so i said exo, n it was wrong..

 

[examkiller]

in physics is the r/ohm graph and x/m graph start at 0. the y axis start at 0 ? or at any point. plz help

0625/06/m/j/09
q3b

 

[examkiller]

what is constant variables in paper 6 physics ? is it temperature of surrounding/thermometer/ and conc. of volume ?

 

[kainat husain]

Thank you, but in The number of moles of MgSO4.xH2O and mass of one mole of MgSO4.xH2O, is there something tricky? don't you need the mass of one mole to find the number? but the question asks to find the number of moles first and not the mass of one mole.

no dear nothing tricky jus look at the equation! like eg- 2CO2+C= 3C
now look in this WE have 3 co2 so when we do the cross mu;ltiply to find the mole we do like
CO2 C
2 1
N x
I HOPE U GOT ME? :/
like we can the num of moles by cross multiplying the above example isnt accurate but still try to get :/

 

[AAnsarii]

what is constant variables in paper 6 physics ? is it temperature of surrounding/thermometer/ and conc. of volume ?

i think so. those dat can vary must b kept constant