QUALITATIVE ANALYSIS....

Question

Give the chemical equation of the following:

-- the pink color of acidified permanganate is decolorized and a yellow-orange toluene layer is obtained.

-- a brown aqueous sol'n and a pink toluene layer upon addition of acidified pemanganate or iron(III)nitrate.

2. in NH3 confirmatory test, only the evolved gas should touch the litmus paper. If the liqiud touches, the result will be a fake positive one. Why? Write the relevant chemical equation and explain.

Answer 1

the pink color of acidified permanganate is decolorized

and a yellow-orange toluene layer is obtained:

first the bromine is produced:

2 KMnO4 & 10 Br-  & 16 H+ --> 2 Mn+2 & 2  K+ & 10 Br2  & 8 H2O

then you shake it with the toluene,  (Bromine dissolved in non-polar solvents like toluene prvoide an orange solution)

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-- a brown aqueous sol'n and a pink toluene layer upon addition of acidified pemanganate or iron(III)nitrate.

first the iodine is produced:

2 KMnO4 & 10 I-  & 16 H+ --> 2 Mn+2 & 2  K+ & 10 I2  & 8 H2O

then you shake it with the toluene,  (Iodine dissolved in non-polar solvents like toluene prvoide a pink to purple  solution)

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2. in NH3 confirmatory test, only the evolved gas should touch the litmus paper. If the liqiud touches, the result will be a fake positive one. Why? Write the relevant chemical equation and explain.

to test whether NH4+ is in the sample we first add NaOH to the sample:

NH4+ & OH- --> NH4OH  --> NH3  & H2O

the NH3 vapor coming out of the NaOH solution in the beaker, dissolves in the water on the litmus, turning it from pink to blue indicating OH- , which we p[resume to have come from:

NH3 & H2O --> NH4OH --> NH4+ & OH-

however if NaOH has splattered & touched the paper ,.. the OH- in its solution will give a false positive , turning the litmus from red to blue.

but the difference is that  OH- from a splattered drop of NaOH touches the paper in one spot & then migrates across the paper.  While the entire paper turns blue at the same time, at the same rate when the beaker is filled with fumes of NH3 & they dissolve into water of the wet litmus