A mixture of solid chlorides was known to contain some or all of the following cations: Ag ,Al^3+Cr^3+,Ca^2+,and/or Zn^2+ . A student performed the following steps: 1.Water was added to the solid and the mixture was stirred well. After several minutes, some of the solid did not dissolve. The mixture was centrifuged and the supernatant was decanted from the solid (solution A). 2. NH4CI(aq) was added to solution A followed by NH3(aq) until the solution was basic to litmus. A gray-green precipitate was formed. The mixture was centrifuged and the supernatant (solution B) was decanted. The solid dissolved in NaOH(aq) and H2O2(aq) to form a light yellow solution. The solution was heated to dryness to remove the H2O2 and the solid was redissolved in HCI(aq). When ammonia was added to make the solution basic, a light yellow solution formed and no solid precipitated. 3. (NH4)2C204(aq) was added to solution B, and a precipitate formed. The mixture was centrifuged and the supernatant (solution C) was decanted. The precipitate from this step dissolved in HCI(aq). A drop of this solution imparted a brick red color to a Bunsen flame. 4. NaOH(aq) was added slowly to (solution C )with constant stirring. A precipitate formed but then dissolved. When a few drops of K4Fe(CN)6(aq) were added to this solution, a grey-blue precipitate formed. For each of the five cations listed on the first line of this question, Identify whether it was definitely present, definitely absent or its presence or absence was unable to be determined in the original solid, after the procedures given above. A confirmatory test for each cation is not required for a determination of definitely present to be made.
A mixture of solid chlorides was known to contain some or all of the following cations: Ag ,Al^3+Cr^3+,Ca^2+,and/or Zn^2+
. A student performed the following steps:
1.Water was added to the solid and the mixture was stirred well. After several minutes, some of
the solid did not dissolve. The mixture was centrifuged and the supernatant was decanted from
the solid (solution A).
2. NH4CI(aq) was added to solution A followed by NH3(aq) until the solution was basic to
litmus. A gray-green precipitate was formed. The mixture was centrifuged and the supernatant
(solution B) was decanted. The solid dissolved in NaOH(aq) and H2O2(aq) to form a light yellow
solution. The solution was heated to dryness to remove the H2O2 and the solid was redissolved in
HCI(aq). When ammonia was added to make the solution basic, a light yellow solution formed
and no solid precipitated.
3. (NH4)2C204(aq) was added to solution B, and a precipitate formed. The mixture was
centrifuged and the supernatant (solution C) was decanted. The precipitate from this step
dissolved in HCI(aq). A drop of this solution imparted a brick red color to a Bunsen flame.
4. NaOH(aq) was added slowly to (solution C )with constant stirring. A precipitate formed but
then dissolved. When a few drops of K4Fe(CN)6(aq) were added to this solution, a grey-blue
precipitate formed.
For each of the five cations listed on the first line of this question, Identify whether it was
definitely present, definitely absent or its presence or absence was unable to be determined in the
original solid, after the procedures given above.
A confirmatory test for each cation
is not required for a determination of definitely present to be made.
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