1. Substances A2+, B2+ and C2+ are all in the same chemical family, and all form

Question

1. Substances A2+, B2+ and C2+ are all in the same chemical family, and all form nitrate salts. In aqueous solurion, the nitrate salts of these cations are colorless and very soluble. Hoee when added to different anions in solution, precipitates sometimes form. The following pattern is observed 1 M Na SO4 1 M Na-CO, 0.25 M NH)CO 0.1 M KIO A2+ aq white white aq slightly cloudy slightly cloudy B2+ aq white very cloudy ag C2+ slightly yellow very cloudy white slightly cloudy white faintly blue very cloudy Key: s - solid (precipitate) forms; aq -aqueous (soluble, no precipitate forms) a. Order these cations (A2*, B2*, and C+) in terms of their solubility. most soluble least soluble b. If you assume that the most soluble cation has the smallest atomic number, order these elements as they would appear in their family on the periodic table. largest 2. You are given an unknown that may contain only one cation A2+, B2+, or C2+, each of whose properties are given in Problem 1 above. You have available to you solutions of Na SO, Na,CO, and (NH)CO Using only two of these solutions, develop a simple procedure for identifying the cation that is present in your unknown. Use the space below to describe your procedure.

Explanation / Answer

1. from the data in the table

a. most soluble B^2+ < A^2+ < C^2+ least soluble

b. arrangement in periodic table

smallest B^2+    A^2+      C^2+   largest

2. Separation of cations,

First add Na2SO4, C^2+ precipitates out of solution

separate the precipitate from the filtrate

Then filtrate was treated with (NH4)2C2O4, A^2+ precipitates out of solution

Separate precipitate

The filtrate now has only B^2+ in it.

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