An unknown solution may contain some of the cations listed
below. One student preformed a series of experiments to determine
what ions are in the solution. Based upon the experiments performed
by the students, the results are as follows:
a) On addition of 6 M HCl, a white precipitate results. The
white precipitate is then mixed with NH3 where it dissolves.
b) On the addition of 1 ml (20 drops) of 1 M thioacetamide
(CH3CSNH2), the test tube was then heated in a boiling water bath
for 5 mins. Removed from heat to cool, then centrifuged the
contents, remove the supernatant (S1) and keep the precipitate. The
precipitate was then rinse in water. 2ml of distilled water was
then added to the precipitate then followed by 15 drops of 6M
potassium hydroxide (KOH). 1 drop of 1 M thioacetamide (CH3CSNH2)
was then added to the precipitate and heated in a water bath for 3
mins. The contents were then centrifuged and the supernatant (S2).
Distilled water was then added to the precipitate followed by 0.75
ml of 6 M NH3. The precipitate dissolves giving a deep blue
color.
c) The supernatant (that is bolded in b (S2) ), 6 M HCl was
then added until the solution turns acidic. No reaction
occurred.
d) The supernatant (that is bolded in b (S1)), 0.75 ml of 5M
ammonium chloride (NH4Cl), 6M NH3 was added until the solution
turned basic and a precipitate was formed. 1 ml (20 drops) of 1 M
thioacetamide (CH3CSNH2), was then added to the precipitate mixed
an then heated in a water bath for 5 mins. The solution was then
cooled, centrifuged and the supernatant (S3) removed. The
precipitate was then washed three times with distilled water. 3ml
(60 drops) of sulfate/hydrogen sulfate (SO42-/HSO4-) buffer was
then added and all of the precipitate dissolved. 6M NaOH was then
added to the solution and a reddish-brown precipitate was observed.
The contents were then centrifuged and the supernatant (S4) was
removed. 2 ml of distilled water was then added to the
reddish-brown precipitate, followed by 1 ml (20 drops) of 6 M HCl,
then 3 drps of 1M potassium thiocyanate (KSCN) and a dark red
solution was then observed.
e) The supernatant (that is bolded in d (S4)), 6M of HCl was
then added, followed by 3M NH3. The solution was then warmed in a
water bath. No precipitate was observed.
Classify the following ions as present, absent, or
undetermined from the observations made above. (input the whole
word)