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Chemistry: Post your doubts here!

biba

biba

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VinnCh said:
Hello, I need help here. For 9701_w09_qp_42 , question 2d (ii), I don't quite get how the question is done.
Click to expand...
um in c (i) we calculated [Ag+] = 7.1x10^-7
now they are asking us to calculate [NH3] that wil give us this value of [Ag+].. and they have given ys the concentration on silver nitrate... here we have to assume that due to ligand substitution silver nitrate got converted into the complex [Ag(NH3)2] so the concentration of this complex is also 0.1 mol/dm3...
ur expression for kc is kc = [Ag(NH3)2] / [Ag+][NH3]^2
u know kc,[Ag+] and [Ag( NH3)2].... find [NH3] (y)
 
VinnCh

VinnCh

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biba said:
um in c (i) we calculated [Ag+] = 7.1x10^-7
now they are asking us to calculate [NH3] that wil give us this value of [Ag+].. and they have given ys the concentration on silver nitrate... here we have to assume that due to ligand substitution silver nitrate got converted into the complex [Ag(NH3)2] so the concentration of this complex is also 0.1 mol/dm3...
ur expression for kc is kc = [Ag(NH3)2] / [Ag+][NH3]^2
u know kc,[Ag+] and [Ag( NH3)2].... find [NH3] (y)
Click to expand...

Ah.. So it it based on an assumption. I understand now. Thanks alot! =)

littlecloud11 said:
When R=H, RNH2= NH3 and [Ag(RNH2)2]+ = [Ag(NH3)2]+
So your Kc expression is -
Kc= [Ag(NH3)2]+/[Ag+] [NH3]^2
The question asks you to find the conc of NH3 when the conc. of silver ions is the same as you answer to ci.
So [Ag+] = ci = 7.1* 10^-7
[Ag(NH3)2] =.1 (given in dii)
therefore
1.7*10^7 = .1/ (7.1*10^-7) * [NH3]^2
[NH3]= .091 mol/dm^3
Click to expand...

Hello, thanks for replying too, but I was actually wondering why do they use [Ag(NH3)2] as 0.1 , but biba explained it to me already, so thanks anyways! =)
 
biba

biba

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VinnCh said:
Ah.. So it it based on an assumption. I understand now. Thanks alot! =)



Hello, thanks for replying too, but I was actually wondering why do they use [Ag(NH3)2] as 0.1 , but biba explained it to me already, so thanks anyways! =)
Click to expand...
welcum !
 
Nab900

Nab900

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iKhaled said:
F
For 4bi..u never did that titration in ur life ?
Click to expand...
i did but wht i actually want to know is that why doesn't the colour change from green to red-brown??? y is it changing to colourless or pale yellow???
 
iKhaled

iKhaled

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Nab900 said:
i did but wht i actually want to know is that why doesn't the colour change from green to red-brown??? y is it changing to colourless or pale yellow???
Click to expand...
idk man thats how i see it when i did the titration and then when u add excess of KMno4 it goes completely dark purple
 
R

raamish

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hey guys can anybody tell me the different purposes of glc, mass spectrometry, nmr, hplc and tlc
 
biba

biba

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raamish said:
hey guys can anybody tell me the different purposes of glc, mass spectrometry, nmr, hplc and tlc
Click to expand...
NMR is used to obtain the information about the number of hydrogen atoms and their chemical environment (to predict the structure of organic molecules ).
MASS SPECTROMETER is used to predict the relative atomic mass of the element,the different isotopes of the element and the relative abundance of the isotopes..
All chromatography techniques are used separate the different components in a copmound by using a mobile phase and a stationary phase..
but in each technique better mobile and stationary phases are used to make the results more reproducible and the separation more efficient.
TLC is similar to paper chromatography (PC) it has the same mobile phase (a polar solvent) as PC but a different stationary phase (slurry of silica or Al2O3),but the separation in TLC is better than that of PC because of the small size of the particles of stationary phase.
GLC uses an inert gas (N2 or Ne) as the mobile phase whereas stationary phase is inert porous diatomaceous rock which is packed in a glass column of narrow diameter (2mm), again the separation in GLC is better than TLC as the narrow diameter ensures the components to b in close contact with both stationary and moblie phase that increases the efficiency of separation... GLC is used to detect drugs in blood.
HPLC uses a high purity solvent as mobile phase that is puped under high pressures in the HPLC instrument , the stationary phase are the porous silica beads packed in a glass column of a narrow diameter, the results of HPLC is better than GLC... HPLC is used in the detection of explosive residues on the skin, it is used in the detection of pesticides in vegetables and fruits!
 
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