Reproduce the table shown below and fill in the information for columns 2 and 3 based on the information provided in the following three paragraphs. An unknown solution possibly contains ions from Groups IV and V. Two drops of 6 M HCl are added to 1.0 mL of this unknown solution, and a white precipitate forms. After centrifuging, the precipitate is separated from the supernatant solution.
Water is added to the precipitate and it is heated. After centrifuging, the supernatant is removed. Next, the precipitate is dissolved in 1 M NH4OH. When this solution is acidified with HNO2, a white precipitate appears. Adding K2CrO4(aq) to the supernatant yields a yellow solution. Next, the supernatant solution from the paragraph above is adjusted to buffered basic conditions by the addition of NH4Cl and/or NH4OH. When (NH4)2CO3 is added, a white precipitate forms. After separation, the precipitate is dissolved in HCl. This solution is made basic with NH4OH. When (NH4)2C2O4 is added, a white precipitate forms. Lastly, when this precipitate is re-dissolved and subjected to a flame test, a red-orange flame is observed.
Present Absent No information
Cation
Why? (be specific)
Ag
Pb2+
Hg2^2+
Ca2+
Mg2+
The instructions for Solution IV describe the preparation of a buffer solution. Calculate the pH of this buffer solution if it has an equal concentration of NH4+ and NH3. Does this solution buffer in the acidic, basic, or nearly neutral pH range? Explain how you decided your answer. Explain why it is necessary to provide a buffer solution at this point in the procedure.