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Biology; Chemistry; Physics: Post your doubts here!

A

***amd***

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FLRNAB said:
11)B
X2 + H2 --> 2HX.
Just read the question and translate the words into a equation.
"One volume of a gaseous element X2" -> 1X2
"an equal volume of gaseous hydrogen" -> 1H2
"form two volumes of a gaseous hydride" -> 2HY

25) "proton number between 21 and 30" --> See the periodic table and these elements are Transition Metals.
Unique Properties of Transition Metals:
1) Form Colored Compounds --> "4. forms two coloured sulfates."
2) Have variable valencies --> "3. forms two basic oxides"
So D

32) C - See Colors of Cations in Syllabus
Blue color of Cu2+ ions
Zinc will displace Hydrogen from HCL as it is more reactive making ZnCl2. Red-Brown can't be the residue because that is color of Iron (III) ions so only option left is grey.

33) B
1) Ar of Nitrogen = 14
Mr of Urea = 60, Percentage by mass = 14/60 * 100 = 23%
Mr of Ammonium nitrate = 80, Percentage by mass = 14/80 * 100 = 17.5
So proportion of nitrogen by mass in Urea is Higher than Ammonium Nitrate.

2)
Moles of Nitrogen in Urea = CH4[N2]O = 2
Moles of Nitrogen in Amm. = [N]H4[N]O3 = 2
So Equal

A5) B) Vanadium is a transition metal so it will form colored compound so solution will be colored.
B7) A)
gatewaysci_18.gif

+ Stopwatch
B8) G) Carbon Monoxide and Water
Click to expand...
B7 (a), why cant we collect the gas with upward displacement of air in a gas jar? coz CO2 is heavier than air.
 
M.Omar

M.Omar

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***amd*** said:
Cu +H2SO4 ---------> CuSO4 + H2
why does Cu replaces H here? even though H is more reactive than Cu.
Click to expand...
Two responses:
One it cud be tht perhaps its CuO,not Cu;Metals below H in EC series do not react with dil acids,but their oxides do.So,in addition,if u ever were to be asked to detail on preparation of CuSO4 then u will need to state CuO,not the pure metal.
The other cud be due to the concentration of H2SO4(which has to be high) which can by-pass the "norm",i.e the expected result and render,instead,a typical telltale acid reactiom
 
A

***amd***

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M.Omar said:
Two responses:
One it cud be tht perhaps its CuO,not Cu;Metals below H in EC series do not react with dil acids,but their oxides do.So,in addition,if u ever were to be asked to detail on preparation of CuSO4 then u will need to state CuO,not the pure metal.
The other cud be due to the concentration of H2SO4(which has to be high) which can by-pass the "norm",i.e the expected result and render,instead,a typical telltale acid reactiom
Click to expand...
hmm.. thanks bro :)
 
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