Physics, Chemistry and Biology: Post your doubts here!

[thats_me]

w04, q 21
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w04_qp_1.pdf
help plz

Look
Ion X is tested , No precipitate is formed so it's not Al3+
It's not SO42- as Bacl2/Ba(NO3)2 is not used
Now , NH4+ or NO3- ?
For NH4+ when we add NaOH ammonia is released and ammonia turs red litmus blue which is not happening here so it's not NH4+
The Ans is NO3-
because :
When NaOH is heated with NO3- there is no visible observation so red litmus stays red
Then when Aluminium powder (i.e metal powder) is added and heated ammonia is evolved which turns red litmus blue

 

[EpicLol]

qn 31; n 32, i noe it's D but y? plz hlp

galvanisation is coating a metal with like zinc to stop rusting and steel mainly contains iron with some carbon and the zinc coz its galvanized therefore its D
I dont know about the other question sry....

 

[AAnsarii]

Look
Ion X is tested , No precipitate is formed so it's not Al3+
It's not SO42- as Bacl2/Ba(NO3)2 is not used
Now , NH4+ or NO3- ?
For NH4+ when we add NaOH ammonia is released and ammonia turs red litmus blue which is not happening here so it's not NH4+
The Ans is NO3-
because :
When NaOH is heated with NO3- there is no visible observation so red litmus stays red
Then when Aluminium powder (i.e metal powder) is added and heated ammonia is evolved which turns red litmus blue

wow

 

[Lost_Life]

ASSISTANCE, PLEASE, ASSISTANCE...
MAY JUNE 2011 VARAINT 12
NUMBER 17 WHY IS IT C NOT A???
X is a monatomic gas.
gas X
Which statement about X is correct?
A X burns in air.
B X is coloured.
C X is unreactive.
D X will displace iodine from potassium iodide.

 

[EpicLol]

ASSISTANCE, PLEASE, ASSISTANCE...
MAY JUNE 2011 VARAINT 12
NUMBER 17 WHY IS IT C NOT A???
X is a monatomic gas.
gas X
Which statement about X is correct?
A X burns in air.
B X is coloured.
C X is unreactive.
D X will displace iodine from potassium iodide.

because monatomic gases are the noble gases(unreactive) and they do not react as they already have 8 valence electrons......so they are unrective....so its C

 

[Maz]

ASSISTANCE, PLEASE, ASSISTANCE...
MAY JUNE 2011 VARAINT 12
NUMBER 17 WHY IS IT C NOT A???
X is a monatomic gas.
gas X
Which statement about X is correct?
A X burns in air.
B X is coloured.
C X is unreactive.
D X will displace iodine from potassium iodide.

The answer's C, since monoatomic gases are usually noble gases.

 

[AAnsarii]

because monatomic gases are the noble gases(unreactive) and they do not react as they already have 8 valence electrons......so they are unrective....so its C

d only monoatomic gases r noble gases?

 

[Maz]

d only monoatomic gases r noble gases?

As far as i know. (excluding compounds of course)

 

[EpicLol]

d only monoatomic gases r noble gases?

yea think so ....

 

[Lost_Life]

another, what about 20?
A solution contains barium ions and silver ions.
What could the anion be?
A chloride only
B nitrate only
C sulfate only
D chloride or nitrate or sulfate

 

[fishcook]

another, what about 20?
A solution contains barium ions and silver ions.
What could the anion be?
A chloride only
B nitrate only
C sulfate only
D chloride or nitrate or sulfate

when the say ions in solutions they mean they are soluble. so the answers B as all nitrates are soluble plus barium sulphate and silver chloride arent soluble.

 

[AAnsarii]

another, what about 20?
A solution contains barium ions and silver ions.
What could the anion be?
A chloride only
B nitrate only
C sulfate only
D chloride or nitrate or sulfate

here u need 2 noe soluble salts, coz of "solun", so AgCl(not balanced) is not soluble, n barium sulfate is insoluble, so ans is B, as all nitrates r soluble, as far as i noe

 

[fishcook]

is the O-level syllabus the same as IGCSE?

 

[fishcook]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w09_qp_11.pdf
why is 13 D?

 

[AAnsarii]

is the O-level syllabus the same as IGCSE?

u takin o level?

 

[Lost_Life]

why

here u need 2 noe soluble salts, coz of "solun", so AgCl(not balanced) is not soluble, n barium sulfate is insoluble, so ans is B, as all nitrates r soluble, as far as i noe

why do you need to soluble salts? i dont get what the question is asking?

 

[AAnsarii]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w09_qp_11.pdf
why is 13 D?

anode is +ve electrode, where Cl ions r attracted. Cl bleaches litmus, so ans is D, as nowhere else it's going clrls

 

[fishcook]

why
why do you need to soluble salts? i dont get what the question is asking?

the Q says they are 'ions' in a solution therefore they have to be soluble otherwise they would be a precipitate. so you just need to determine which compounds are soluble and which are insolube

 

[fishcook]

anode is +ve electrode, where Cl ions r attracted. Cl bleaches litmus, so ans is D, as nowhere else it's going clrls

but Cl2 bleaches litmus paper.. is it the same for universal indicator?

 

[AAnsarii]

why
why do you need to soluble salts? i dont get what the question is asking?

c, they just want 2 c dat u notice solution, so solution will only b d case where d dissolved solute(s) is/r soluble. here comes d soluble/insoluble stuff. i hp u noe what salts r soluble n the rest which arent, if u dont tell