4. (8 pts) You are working in a different experiment with a solution that contai
ID: 561910 • Letter: 4
Question
4. (8 pts) You are working in a different experiment with a solution that contains Na,SO, and NaOH. Describe how you would separate the two anions (sulfate and hydroxide) and confirm the presence of each. Answer the following to help you design your procedure a. What reagents could you add to precipitate each one? b. Which reagent should be added first and why? c. Write the equations for the reactions that would take place, and use this link ) to describe the observation you would expect to see to confirm the presence of each ion. d. Clearly describe the procedure you would follow to separate the two anions.Explanation / Answer
a) A solution of barium chloride, BaCl2 can be added to the mixture to precipitate sulfate anion (SO42-) as barium sulfate, BaSO4.
After the solid is filtered off, a solution of ferric chloride, FeCl3 can be added to the solution to precipitate hydroxide anion (OH-) as ferric hydroxide, Fe(OH)3.
b) BaCl2 reacts with both Na2SO4 and NaOH to form BaSO4 and barium hydroxide, Ba(OH)2. Ba(OH)2 is soluble in water and goes into the solution while BaSO4 precipitates out.
We do not add FeCl3 at the beginning because it produces ferric sulfate, Fe2(SO4)3 and Fe(OH)3. Fe2(SO4)3 is sparingly soluble in water and co-precipitates with Fe(OH)3; hence, the purpose will be defeated.
c) The balanced chemical equations for the reactions are shown below.
BaCl2 (aq) + Na2SO4 (aq) --------> BaSO4 (s) + 2 NaCl (aq)
BaCl2 (aq) + 2 NaOH (aq) --------> Ba(OH)2 (aq) + 2 NaCl (aq)
3 Ba(OH)2 (aq) + 2 FeCl3 (aq) --------> 2 Fe(OH)2 (s) + 3 BaCl2 (aq)
d) Take the mixture of Na2SO4 and NaOH in a test tube and add BaCl2 solution dropwise until precipitation is complete. Filter the precipitate and retain the filtrate.
Wash the precipitate with water (or brine) and dry to obtain solid BaSO4.
Add FeCl3 to the filtrate; a precipitate occurs. Continue adding FeCl3 until the precipitation is complete. Filter the precipitate, wash with water and dry to obtain pure Fe(OH)3.
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