A student collects the experimental data above to determine the ions present in

Question

A student collects the experimental data above to determine the ions present in an unknown solution. The unknown solution contains one each of the following cations and anions: Pb^1+, Cd^2+, NH_4^+, H^+ or K^+ and S^2, CO_3^2, I, OH, or NO_3. The anion present can be determined by testing with one solution. Identify the solution to use, and explain why the results of adding that one solution to the unknown will allow you to you eliminate all other possibilities and conclusively identify the anion present. A student is given an unknown solution with the same possible cations and anions listed above in problem #1 above. The student tests his unknown solution first using cadmium nitrate to a fresh sample of the unknown then adding lead (II) nitrate to a fresh sample of the unknown. Both tests result in a cloudy white precipitate. a. Write the formula of the anion present in his unknown: b. Write the formulas for the possible cations present in his unknown: c. Explain how the student can determine the cation present in his unknown using only red litmus paper and a beaker with hot tap water.

Explanation / Answer

1.

Use Pb(NO3) because it gives different result for all 4 types of anions.

2.

a) Anion present in the unknown = OH-

b) Only a relatively stronger base can produce OH- that can precipitate with Pb(NO3) and Cd(NO3). Therefore possible cations are K+ and NH4+. Pb2+ and Cd2+ are sparingly soluble and will not produce enough OH-.

c)

Only KOH will turn red litmus paper blue in hot water.

If the red litmus paper turns blue, the cation is K+ else the cation is NH4+.

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