Chem Paper 6 Question

[Saturation]

Hi everyone!
Can someone please explain to me how to do question 5
[url=http://www.xtremepapers.net/C...w.xtremepapers.net/CIE/Cambrid ... 7_qp_6.pdf[/url]

Is this question in this paper one of the harder questions compared to the similar ones in other papers?, cause didnt have much trouble with the other papers :roll:

THanks in advance

 

[ibrahim]

in part c CO2 is produced because solid C contained insoluble lead carbonate ,solid D.
so when HNO3 is added a fizz and bubbles of gas can be seen because a the reaction of an acid with a carbonate.
the test for CO2 is limewater, +ve result if turns milky/cloudy.

i dont get part d :S

part f is CO2 as ive already mentioned

part g is ammonia because aq.NaOH, Aluminium foil and gentle heat is test for ammonia gas, and +ve result is when litmus paper turns from red to blue and a gas is given off.

part h is iron 2+ because it has been tested with NaOH and a green ppt. has been formed, and ammonium ions were present becuase ammonia was given off with the given test, and sulphate ions are present becuase dil. HCL and Ba(NO3)2 has been added and a white ppt. was formed.

 

[Saturation]

ThANK You !, I really need to find out part d though :roll:

 

[ibrahim]

welcome xD
ill try to find out too.

 

[Pierre Samy]

will i got a trouble in Nov 2003 ( specimen paper ) Q4(g)
if any one could help
thanks in advance

 

[waleedsmz]

as for part D, the residue is lead carbonate, so when potassium iodide is added in an acidic medium ( made by nitric acid ) , a yellow ppt of lead iodide will be formed. It's as if you're testing for iodide ions, just backwards.

 

[Saturation]

Thank you! I got it!! When they add nitric acid to the reisdue( lead carbonate), lead nitrate is formed. then when potassium iodide is added to the residue, a yellow ppt. of barium iodide is formed!
This is what takes place right?!!

Thank you!

Oh btw, what is the purpose of "acidifying" before testing for an anion? :roll:

 

[waleedsmz]

honestly, I have no idea! but the yellow ppt isn't barium iodide! From where did you get the Barium anyway?

 

[Saturation]

Whoops! Sorry! It's actually a yellow ppt. of lead iodide right?

 

[ibrahim]

yup its lead iodide not barium iodide