Chemistry Paper4 discussion

[srukhan]

Okay peeps, It's much easier to follow this way. Get down your doubts and troubles together and lets get cracking
I'll do the honours and start with my dispute which atm is with Q8 from June 2009, part c) ii)

 

[WellWIshER]

GUYS WTH!!!

oct 07 q3 part c 2 and 4

how IS IT POSSIBLE TO OXIDIZE CL AND REDUCE CHROMATE WHEN DA E VALUE OF CL IS GREATER THAN CR+


wt is going on????

 

[zeebujha]

It is possible when we use CONENTRATED HCl. The standard E values apply for concentration of 1mol/dm3. However, is we use the concentration far greater in excess of 1mol/dm3 , the E value of Cl2/Cl- becomes less positive as the equilibrium lies well to the left dude to the very high concn of Cl- (Le chateleier's principle). So, while the standard E values would give cell potential of -0.03, the smaller value of the Cl2/Cl- in this particular case, makes the cell potential positive.

The question does hint at this by asking later why we cannot do this using DILUTE HCl!

 

[zeebujha]

Okay peeps, It's much easier to follow this way. Get down your doubts and troubles together and lets get cracking
I'll do the honours and start with my dispute which atm is with Q8 from June 2009, part c) ii)

(i)4
The cross given is useful to start the thought process. Draw a horizontal line in the figure from the cross. The first separation would have resulted in separation along the line
That line becomes the initial starting point for the second chromatography.
Thus, the number of columns of dots arising from the second chromatography is in fact equal to the number of spots from the first run.

(ii)the first column (on the left). The spot on the top

(iii) the fourth column (on the right). The only spot.

 

[kugs]

can someone please explain how to solve q8 c (ii) and d (iv)?
http://www.xtremepapers.me/CIE/International A And AS Level/9701 - Chemistry/9701_w09_qp_42.pdf

and also
http://www.xtremepapers.me/CIE/Internat ... _qp_42.pdf
q6, d

 

[devilishangel]

Can someone please answer d following

Q: Discuss the benefits of using bacterial leaching over the use of cyanide

 

[stxjunk]

About the Cyanide versus bacterial leaching:

• Bacterial leaching has helped extract gold from the ore with an efficiency of 80-100% while cyanide has proved to be only a maximum of around 10% efficient.
  Bacterial leaching avoids complicated extraction processes, mainly because you use only a batch fermenter for aiding the bacteria.
  It is a less complicated process, and more economically beneficial way of gold extraction. Considering the 12 principles of green chemistry, it can be said that it supports almost all of those rules.

 

[MukeshG93]

About the Cyanide versus bacterial leaching:

• Bacterial leaching has helped extract gold from the ore with an efficiency of 80-100% while cyanide has proved to be only a maximum of around 10% efficient.
  Bacterial leaching avoids complicated extraction processes, mainly because you use only a batch fermenter for aiding the bacteria.
  It is a less complicated process, and more economically beneficial way of gold extraction. Considering the 12 principles of green chemistry, it can be said that it supports almost all of those rules.

Also, no labor force required. There are no toxic wastes and complicated machinery is not required, which SHARPLY cuts down the danger of the process.