You are given an unknown solution that only contains one of the two listed cations. Describe a simple test to distinguish between aqueous solutions of the following cations. State the distinguishing outcomes of the test and the indication of which cation is present. a: Al^3+ and Fe^3+ b: Fe(OH)3(s) and Ni(OH)2(s) c: Cr^3+ and CrO4^2- d: Ni^2+ and Fe^3+
Al^3+ and Fe^3+. Most iron(III) solution are lightly colored while Al&3+ solutions are not; however, if you want a more definitive test, add OH^-. Iron(III) hydroxide is red/brown while aluminum hydroxide is white.
Fe(OH)3 and NI(OH)2 --not the same color.
Cr^3+ and CrO4^2- --not the same color.
Ni^2+ and Fe^3+. -different color.
To distinguish between aqueous solutions of different cations, you can perform various tests or experiments that exploit the unique chemical properties of each cation. Here are simple tests for each pair of cations you mentioned:
a. Al^3+ and Fe^3+:
To distinguish between Al^3+ and Fe^3+ ions, you can use a reagent called sodium hydroxide (NaOH).
Test: Add a few drops of NaOH solution to the unknown solution containing either Al^3+ or Fe^3+ cations.
Distinguishing Outcomes:
- Al^3+ cation: When NaOH is added to an Al^3+ solution, a white precipitate of aluminum hydroxide (Al(OH)3) will form.
- Fe^3+ cation: When NaOH is added to an Fe^3+ solution, a reddish-brown precipitate of iron (III) hydroxide (Fe(OH)3) will form.
The presence of a white precipitate indicates the presence of Al^3+ ions, while the formation of a reddish-brown precipitate confirms the presence of Fe^3+ ions.
b. Fe(OH)3(s) and Ni(OH)2(s):
To distinguish between Fe(OH)3 and Ni(OH)2, you can use acid to test the solubility of the precipitates formed.
Test: Add a dilute acid, such as hydrochloric acid (HCl), to the solid precipitates of either Fe(OH)3 or Ni(OH)2.
Distinguishing Outcomes:
- Fe(OH)3: When HCl is added to Fe(OH)3, the precipitate of iron (III) hydroxide will dissolve, forming a yellowish solution.
- Ni(OH)2: When HCl is added to Ni(OH)2, the precipitate of nickel (II) hydroxide will not dissolve.
The dissolution of the precipitate and the formation of a yellowish solution confirm the presence of Fe(OH)3. The lack of dissolution indicates the presence of Ni(OH)2.
c. Cr^3+ and CrO4^2-:
To distinguish between Cr^3+ and CrO4^2-, you can use a reagent called silver nitrate (AgNO3).
Test: Add a few drops of AgNO3 solution to the unknown solution containing either Cr^3+ or CrO4^2-.
Distinguishing Outcomes:
- Cr^3+ cation: When AgNO3 is added to a Cr^3+ solution, no visible reaction occurs.
- CrO4^2- anion: When AgNO3 is added to a CrO4^2- solution, a bright yellow precipitate of silver chromate (Ag2CrO4) will form.
The absence of any visible reaction indicates the presence of Cr^3+ ions. The formation of a bright yellow precipitate confirms the presence of CrO4^2-.
d. Ni^2+ and Fe^3+:
To distinguish between Ni^2+ and Fe^3+, you can use a reagent called sodium hydroxide (NaOH).
Test: Add a few drops of NaOH solution to the unknown solution containing either Ni^2+ or Fe^3+.
Distinguishing Outcomes:
- Ni^2+ cation: When NaOH is added to a Ni^2+ solution, a light green precipitate of nickel (II) hydroxide (Ni(OH)2) will form.
- Fe^3+ cation: When NaOH is added to an Fe^3+ solution, a reddish-brown precipitate of iron (III) hydroxide (Fe(OH)3) will form.
The formation of a light green precipitate indicates the presence of Ni^2+ ions, while the presence of a reddish-brown precipitate suggests the presence of Fe^3+ ions.
Remember, these are general tests that can help distinguish between the given cations. However, it is always advisable to consult specific lab protocols and reference materials for accurate identification of cations.