Question

In this experiment, the goal is to separate and isolate groups of cations with similar properties. To isolate the soluble cations of sodium and potassium ions, what method is used to precipitate all other cations?

A. Add hydrochloric acid to precipitate the cations with excess chloride ions.
B. Make the solution basic with aqueous ammonia to precipitate the cations.
C. Reduce the cation with a stannite solution to make a black precipitate of the unwanted cations.
D. Make the solution basic to form insoluble hydroxide salts or oxides.
E. Add hydroxide to the solution to shift the equilibrium, releasing the unwanted cations as a gas.
F. The addition of potassium hexacyanoferrate(II) forms a red-brown precipitate of the excess cations.

Answer 1

To isolate sodium and potassium ions, selective precipitation is used, often by making the solution basic to form insoluble hydroxide salts or oxides, thus precipitating other cations. D. Make the solution basic to form insoluble hydroxide salts or oxides.

Step-by-step explanation:

To isolate soluble cations such as sodium and potassium ions, we can employ the method of selective precipitation. This method involves adding reagents that will cause the precipitation of certain cations while leaving others in solution. One common way to precipitate many cations aside from sodium and potassium is by making the solution basic, which often leads to the formation of insoluble hydroxide salts or oxides that can then be separated from the solution. An example includes Group 1 cations such as Ag+, Pb2+, and Hg22+, which form insoluble chlorides when hydrochloric acid is added, thus falling out of solution as a precipitate.

By carefully controlling the pH and other conditions, selective precipitation can be used to separate metal ions based on their solubility products, or Ksp values. Some cations will precipitate before others based on their unique chemical interactions with the added reagents. The remaining soluble ions, like sodium and potassium, can be further analyzed or used as desired once the other cations have been removed.

Answer 2

To isolate soluble sodium and potassium ions from other similar cations, Option B is correct: Make the solution basic with aqueous ammonia to precipitate the cations. This process relies on selectively precipitating other cations as insoluble hydroxide salts or oxides through controlled pH adjustments.

Step-by-step explanation:

Chemical Separation of Metal Ions

To isolate the soluble cations of sodium and potassium ions, the precipitation method is utilized to separate and remove other cations that have similar properties but are less soluble. When we consider a mixture of metal ions in a solution, it is possible to separate these ions by selectively precipitating them with specific anions such as Cl⁻, Br⁻, SO₄²⁻, CO₃²⁻, S²⁻, Cr₂O⁷²⁻, PO₄³⁻, OH⁻, and so on. This method works because when a metal ion or a group of them forms an insoluble salt with a particular anion, they can be separated from the rest by precipitation.

One example is the selective precipitation of group 1 cations, which involves making the solution basic with aqueous ammonia to precipitate the cations as insoluble hydroxide salts or oxides. This process can separate cations like Ag+, Pb2+, and Hg22+ as insoluble chlorides from sodium and potassium ions. In this specific case, the correct option to precipitate all other cations except the soluble sodium and potassium ions would be Option B, to make the solution basic with aqueous ammonia to precipitate the cations, thus isolating the desired sodium and potassium ions. By carefully controlling the pH of the solution and exploiting the differences in solubility products (Ksp), we can selectively precipitate out the unwanted ions.