Question

,

? – To precipitate their Group C cation- Ca, Ba,

Sr a fellow student adds 1M (NH4)2SO4 and no precipitate forms. The student then

adds saturated ammonium oxalate and a white precipitate forms. What is the most likely identity of the Group C cation?

What would you instruct the student to do to confirm the identity? Specific instructions along with observations are needed.

Background info:

Background Chemistry and Discussion

After removing the Group A and Group B cations from your unknown by precipitation, the Group C and D cations remain in

solution. The three ions; Ca2+, Sr2+ and Ba2+, that make up Group C have soluble chlorides and hydroxides that are reasonably

soluble in ammonia solutions. These three ions can be separated from the Group D ions by selective precipitation.

Identification of your Group C cation based solely upon the color of the precipitate formed is not possible since the

precipitates formed by Ca2+, Sr2+ and Ba2+ do not have colors unique from each other. Identification can be achieved by using

a combination of solubility behavior and flame tests. You are required to develop a scheme that will allow you to separate

and correctly identify the Group C cation present in your unknown solution.

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