Separating mixtures by precipitation
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Intros
Examples
Lessons
- Use tables of solubility to suggest ways to separate ions from aqueous mixtures.
Below is a table of solubilities, showing which combinations of aqueous ions will result in a precipitate when mixed.
A series of experiments were performed with solutions containing different unknown combinations of the four cations in the first column.Cl-/Br-/I-
SO42-
S2-
OH-
PO43-
Ba2+ (aq)
-
Ppt
-
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Pb2+ (aq)
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Ppt
Ppt
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Ag+ (aq)
Ppt
Ppt
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Ni2+ (aq)
-
-
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Sr2+ (aq)
-
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-
-
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Mg2+ (aq)
-
-
-
Ppt
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- The anions (across the first row) are added in the form of soluble salts that dissolve to give the aqueous anion we need.
Explain why sodium salts are a good source of the anions in this experiment. - A solution contains Pb2+(aq), Sr2+(aq) and Ni2+ (aq). Which anions and in which order should be added to separate these cations?
- The anions (across the first row) are added in the form of soluble salts that dissolve to give the aqueous anion we need.
- Use tables of solubility to predict precipitates formed from experiments.
Below is a table of solubilities, showing which combinations of aqueous ions will result in a precipitate when mixed.
A series of experiments were performed with solutions containing different unknown combinations of the four cations in the first column.Cl-/Br-/I-
SO42-
S2-
OH-
PO43-
Ba2+ (aq)
-
Ppt
-
Ppt
Ppt
Pb2+ (aq)
Ppt
Ppt
Ppt
Ppt
Ppt
Ag+ (aq)
Ppt
Ppt
Ppt
Ppt
Ppt
Ni2+ (aq)
-
-
Ppt
Ppt
Ppt
Sr2+ (aq)
-
Ppt
-
-
Ppt
Mg2+ (aq)
-
-
-
Ppt
Ppt
- A solution with two of the above cations present was mixed with the following anions, with the results below:
- Chloride (Cl-) ions were added. No precipitate was observed.
- Sulfate ions (SO42-) were added. No precipitate was observed.
Which two cations must be present in the solution? - A solution with two of the above cations present was mixed with the following anions, with the results below:
- Chloride (Cl-) ions were added. No precipitate was observed.
- Sulfide (S2-) ions were added. A precipitate formed in this mixture and was filtered off.
- Hydroxide (OH-) ions were added. No precipitate was observed.
What is the precipitate formed with the sulfide ion?
What is the identity of the remaining cation?
- A solution with two of the above cations present was mixed with the following anions, with the results below: