A student was given a solid containing a mixture of nitrate salts. The sample co
ID: 589605 • Letter: A
Question
A student was given a solid containing a mixture of nitrate salts. The sample completely dissolved in water, and upon addition of dilute HCI, no precipitate formed. The pH was lowered to about 1 and H2S was bubbled through the solution. No precipitate formed. The pH was adjusted to 8 and H2S was again bubbled in. This time, a precipitate formed Which compounds might have been present in the unknown? Incorrect. Zn(NO3)2 KNO3 Sn(NO3)4 Fe(NO3)3 Ca(NO3)2 AgNO3 Pb(NO3)2 Cr(NO3)3 Start by selecting all choices, then unselect only the ones that you can rule out for sure. Since no precipitate formed upon the addition of HCI, we can rule out any cations that form insoluble chlorides Since the addition of H2S did not yield a precipitate in acidic conditions, we can rule out any cations that form acid-insoluble sulfides See the flowchart in the bottom panel for more detailsExplanation / Answer
If no HCl forms, there are no Ag+, Pb+2, Hg+2 or Hg2+2 present... (GROUP I)
if pH = 1, then H2S is added...(GROUP II) .. Hg2+, Bi3+ , Cu2+ , Cd2+ are not present...
if we adjust pH to 8, then add H2S,
a precipitate forms...
this could be --> Co2+, Ni2+, Fe3+, Mn2+, Cr3+, Al3+, Zn2+
Sn+4 --> Sn+4 could be present
Cr+3 = --> could be
Zn+2 = could be, since group III
Ca+2 = could be since it requires flame test
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