An unknown is treated according to the procedure of this experiment. At each ste
ID: 1056275 • Letter: A
Question
An unknown is treated according to the procedure of this experiment. At each step described below, state what Group I cation may be present, which are definitely present, and which are definitely absent. Remember, these are sequential steps! (Use a flow chart to answer the questions >) The white chloride precipitate is washed and treated with hot water. A white precipitate and colorless suppurate results. The supernatant from step a is treated with K_2CrO_4. A clear, yellow solution results. The precipitate from step a is treated with NH_3(aq). A black precipitate and a colorless solution result. The solution from (c) is treated with HNO_3. A white precipitate forms. Ions definitely In the step where Ag^+ and Hg_2^2+ are being separated by addition of 6M NH_3. a student obtains a black precipitate and a clear, colorless supemate. The student concludes that both captions are definitely present Assess the student's conclusions for their accuracy. Explain why the student is correct or incorrect forExplanation / Answer
Step a:
When the white chloride precipitate is washed and treated with hot water, PbCl2 can be separated from the other two chlorides by adding hot water. In hot water, PbCl2 will dissolve while AgCl and Hg2Cl2 remain insoluble.
Ions definitely present is: Pb2+
Ions definitely absent is: Ag+ and Hg22+
Step b:
The supernate from step a is treated with K2CrO4, results a clear yellow solution.
Ions definitely present is: Pb2+
Ions definitely absent is: Ag+ and Hg22+
Step c:
The precipitate from step a is treated with NH3, results a black precipitate and a colorless solution.
Ions definitely present: Hg22+
Ions definitely absent is: Ag+ and Pb2+
Step d:
The solution from (c) is treated with HNO3, forms a white precipitate.
Ions definitely present: Ag+
Ions definitely absent is: Hg22+ and Pb2+
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