Results The project has shown the presence of 5 cations: lead, mercury, bismuth, cobalt, zinc, and calcium. For Project A, the presence of lead and mercury were evident. To confirm lead’s presence, the original precipitate had to be washed and heated. Lead is known to easily dissolve in warm temperatures compared to the other metals present in the precipitate. The supernatant with the lead was separated from the precipitate and acetic acid was quickly added. The acid was used to make the lead more soluble in solution: + ¿ Pb ( s )+ CH ₃ COOH ( aq ) →PbCOOH ( aq )+ C H 3 ❑ ¿ K CrO was added to act as the final confirmation of lead’s presence: ₂ ₄ + ¿ + COOH ⁻ PbCOOH ( aq )+ K 2 CrO 4 ( aq ) →PbCr O 4 ( s )+ 2 K ¿ (1)
To confirm the presence of mercury, ammonia is added to create the mercury precipitate: Hg 2 Cl 2 (s) + NH 3 (aq) → Hg(l) + HgNH 2 Cl(s) + HCl(aq) (2) For Project B, only bismuth was present. It was confirmed by first adding aqueous KOH to the white precipitate isolated from the previous step to create a complex: + ¿ OH ¿ 3 ( aq )+ K ¿ 3 + ¿ ( aq )+ KOH ( aq ) →Bi ¿ Bi ¿ Tin(II)chloride was then added to reduce the bismuth solution to create the precipitate: OH ¿ 3 ( s ) → 2 Bi ( s )+ 3 Sn ( OH ) ₆ ² ⁻ ( aq ) 3 Sn ( OH ) ² ₄ ⁻ ( aq )+ 2 Bi ¿ (2)
For Project C, cobalt and zinc were found in the unknown solution. Since silver was absent in Project A, the only other element that could create a blue hue was cobalt. After separating the cobalt and nickel from one another, ammonium thiocyanate was added to create a cobalt complex which made the solution turn blue: 2 − ¿ + 4 NH ₄ ⁺ NCS ¿ 4 ¿ ¿ Co ¿ 2 + ¿ ( aq )+ 4 N H 4 SCN ( aq ) → ¿ Co ¿ To confirm the presence of zinc, after getting its purified solution formula, aqueous HCl was added to acidify the environment to make zinc more soluble. K [Fe(CN) ] was added to become ₄ ₆ the final confirmation solution for the creation of the zinc precipitate: + ¿ Fe ¿ ( s )+ 4 K ¿ Fe ¿ → Zn 2 ¿ 2 Zn ( s )+ K 4 ¿
For Project D, the procedure confirmed 1 metal: calcium. Calcium ions were extracted after meticulous washings, and steps taken to make the solution turn acidic and then basic. (NH ) C O is added to have the chromate attach to the calcium and create the white precipitate: ₄ ₂ ₂ ₄ N H 4 ¿ 2 C 2 O 4 ( aq ) →Ca ( C 2 O 4 )( s )+ 2 NH ₄ ⁺ 2 + ¿ ( aq )+ ¿ C a ¿ An important thing to note was a very small amount of calcium was extracted, and may be due to impurities removed inappropriately.
Discussion Although students have learned to extract different metal ions, it is important to acknowledge the true purpose of this experiment: to separate elements based on their properties. Some require separation by temperature while others need to be under acidic or alkaline environments. Some can be separated as easy as adding a chemical while others require rigorous cleaning, extractions and multiple chemicals to reveal them. Regardless, it is a critical technique to use and master in an environment where chemicals are highly involved. These techniques can be applied for purification, extraction and isolating components. This experiment has also taught individuals the meticulous attention to detail and time management necessary to complete large jobs. One must
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- Spring '16
- Dr. S. Menon
- Solubility, Ion