Chemistry Doubts: Paper 1 & 2

[salman1996]

some1 pls explain : Q 31 paper 1 nov 07

 

[salman1996]

Do we need to remember the colours of some compounds like FeSO4, CuO, BaSO4 etc.?

 

[Buland Iqbal]

Do we need to remember the colours of some compounds like FeSO4, CuO, BaSO4 etc.?

Yes, green for FeS04, black for CuO and white for BaS04. Simple as that

 

[sourov97]

thanks for explaining. one more pls: Q 28 http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s07_qp_1.pdf

Firstly, hydrogen is a reducing agent and can reduce compounds of metals less reactive than it.
question says another substance (liquid) was formed after passing H2... means that sth reacted with the powdered solid.
as H2 was passed, the solid must be reduced to produce another product...the solid must be CuO (less reactive than H)
hope it helps

 

[Salman Rahman]

Do we need to remember the colours of some compounds like FeSO4, CuO, BaSO4 etc.?

not really memorize, but u can guess them like most metal oxides are dark in colour (CuO Fe2O3), FeSO4 should be green as the test for Fe2+ is green ppt,
u should know the tests for ions and the colours can be predicted from those (BaSO4 is white solid /test for SO4 radicals, Fe2SO4 is red-brown, NaCl is white/Cl- test)

 

[Shadman Azad]

in displacement reactions for halogen, is there always a colour change? if yes, it means that we have to memorize all the colours of hologens?

 

[sourov97]

in displacement reactions for halogen, is there always a colour change? if yes, it means that we have to memorize all the colours of hologens?

yes...u have to learn the colour of halogens in aqueous compounds...

 

[Shadman Azad]

yes...u have to learn the colour of halogens in aqueous compounds...

do u know the colours changes?...can u post the important ones pls?

 

[sourov97]

do u know the colours changes?...can u post the important ones pls?

In displacement reactions for halogens, the colour change to the colour of more reactive halogen.

Flourine is a pale yellow gas at rtp
Chlorine is a greenish gas at rtp
Bromine is a reddish liquid at rtp
Iodine is black solid at rtp
Astantine is a shiny black solid at rtp

Example: 2KBr + Cl2 = 2KCl + Br2(aq) .... solution turns red
2KI + Br2 = 2KBr + I2(aq) .... solution turns *brown*
*** iodine forms brown solution in water and purple vapour when heated .
hope it helps

 

[Shadman Azad]

In displacement reactions for halogens, the colour change to the colour of more reactive halogen.

Flourine is a pale yellow gas at rtp
Chlorine is a greenish gas at rtp
Bromine is a reddish liquid at rtp
Iodine is black solid at rtp
Astantine is a shiny black solid at rtp

Example: 2KBr + Cl2 = 2KCl + Br2(aq) .... solution turns red
2KI + Br2 = 2KBr + I2(aq) .... solution turns *brown*
*** iodine forms brown solution in water and purple vapour when heated .
hope it helps

thanks surely this helps.

 

[Salman Rahman]

do we need to learn the tests for Ba2+ Ca2+ Pb2+ and I- Br- ions...these are not seen often in past papers?

 

[sourov97]

do we need to learn the tests for Ba2+ Ca2+ Pb2+ and I- Br- ions...these are not seen often in past papers?

For cations, learn the tests for iron (both oxidation state), copper(II), aluminium (which is the same as Pb), Zinc, calcium and ammonium ions
anions: chloride, iodide, bromide, nitrate, sulphate and carbonates.

 

[Anam Iqbal]

please suggest me a good chemistry teacher ........I am gonna fail it really bad

 

[gGazal Niz]

well i was facing the same problem few weeks ago but someone suggested me PACANS. i don't know its a good institute or not for other subjects but for chemistry there's a Female teacher. Her way of teaching is quiet good and i am happy to say that i am now 80% prepared for chemistry paper.

 

[sourov97]

please suggest me a good chemistry teacher ........I am gonna fail it really bad

well i was facing the same problem few weeks ago but someone suggested me PACANS. i don't know its a good institute or not for other subjects but for chemistry there's a Female teacher. Her way of teaching is quiet good and i am happy to say that i am now 80% prepared for chemistry paper.

well....for o level chemistry, our coursebooks are sufficient...besides, to me, this is the easiest science sub...
but if are having problems, u can try out red spot's chemistry key points and topical papers.
the teacher of my school are brilliant in chemistry, though they are not effective for physics...sorry i cant suggest any tutor cause i am from bangladesh
but if u have any queries with any topics u can ask here...i shall try my best

 

[sourov97]

please suggest me a good chemistry teacher ........I am gonna fail it really bad

check this out, sort out ur problems from the detailed syllabus fragments starting page 10 and share it here, sm1 might help

 

[Salman Rahman]

In displacement reactions for halogens, the colour change to the colour of more reactive halogen.

Flourine is a pale yellow gas at rtp
Chlorine is a greenish gas at rtp
Bromine is a reddish liquid at rtp
Iodine is black solid at rtp
Astantine is a shiny black solid at rtp

Example: 2KBr + Cl2 = 2KCl + Br2(aq) .... solution turns red
2KI + Br2 = 2KBr + I2(aq) .... solution turns *brown*
*** iodine forms brown solution in water and purple vapour when heated .
hope it helps

good job! thanks

 

[Salman Rahman]

help please:
(a) why ozone is important in terms of human health? [2]
(b) write the reaction for the conversion ozone to oxygen by CFC?

 

[Shadman Azad]

help please:
(a) why ozone is important in terms of human health? [2]
(b) write the reaction for the conversion ozone to oxygen by CFC?

is this included in our syllabus? ....ozone prevent harmful rays...(b) O3 + Cl2 = Cl2O + O2 (unsure)

 

[Shadman Azad]

sourov97 what are the sources and effects of atmospheric pollutants?