Question

Construct the flow diagram for the separation scheme for a solution containing \(\mathrm{Ag}^{+}, \mathrm{Ni}^{2+},\) and \(\mathrm{Zn}^{2+}\). The steps in the procedure are as follows: Step 1. Add \(6 \mathrm{M}\) HCl to precipitate \(\mathrm{Ag}^{+}\) as \(\mathrm{AgCl}\). \(\mathrm{Ni}^{2+}\) and \(\mathrm{Zn}^{2+}\) are not affected. Centrifuge out the AgCI. Step 2. Add 6 M NaOH in excess, precipitating Ni(OH), (s) and converting Zn't to the Zn(OH), \(_{4}^{2-}\) complex ion. Centrifuge out the \(\mathrm{Ni}(\mathrm{OH})_{2}\) Step 3. Neutralize the solution with \(6 \mathrm{M}\) HCl to \(\mathrm{pH}=7 .\) Add \(1 \mathrm{M} \mathrm{Na}_{2} \mathrm{CO}_{3}\), precipitating \(\mathrm{ZnCO}_{3}\) diagram

Short answer

To construct a flow diagram for the separation scheme of a solution containing Ag⁺, Ni²⁺, and Zn²⁺ ions, follow these steps: 1. Initial solution: (Ag⁺, Ni²⁺, Zn²⁺) 2. Add 6M HCl: Precipitate AgCl (Ni²⁺, Zn²⁺ in solution) 3. Centrifuge: Remove AgCl 4. Add 6M NaOH: Precipitate Ni(OH)₂, form Zn(OH)₄²⁻ complex ion 5. Centrifuge: Remove Ni(OH)₂ 6. Add 6M HCl: Neutralize to pH 7 7. Add 1M Na₂CO₃: Precipitate ZnCO₃ 8. Separated ions: Ag⁺ as AgCl, Ni²⁺ as Ni(OH)₂, and Zn²⁺ as ZnCO₃

Step-by-step solution

Add 6M HCl and precipitate AgCl

First, add 6M HCl to the initial solution containing Ag⁺, Ni²⁺, and Zn²⁺ ions. The HCl will react with Ag⁺ to form insoluble AgCl, which will precipitate out of the solution. The other ions, Ni²⁺ and Zn²⁺, will not be affected by this step. Next, centrifuge the mixture to separate the AgCl precipitate from the solution.

Add 6M NaOH and precipitate Ni(OH)₂

Add 6M NaOH in excess to the remaining solution after centrifugation. This will cause the Ni²⁺ ions to react and form insoluble Ni(OH)₂, which will precipitate out of the solution. At the same time, Zn²⁺ ions will form a soluble complex ion Zn(OH)₄²⁻. After this reaction, centrifuge the mixture again to separate Ni(OH)₂ precipitate from the solution.

Neutralize the solution and precipitate ZnCO₃

Neutralize the remaining solution with 6M HCl to adjust its pH to 7. After achieving the desired pH, add 1M Na₂CO₃ to the solution. This will cause the Zn(OH)₄²⁻ ions to react and form insoluble ZnCO₃, which will precipitate out of the solution.

Flow Diagram Representation

Create a flow diagram showing the step-by-step separation process visually: 1. Start with the initial solution containing Ag⁺, Ni²⁺, and Zn²⁺ ions. 2. Show the addition of 6M HCl and the formation of AgCl precipitate. 3. Demonstrate the centrifugation step to remove AgCl. 4. Show the addition of 6M NaOH and the formation of Ni(OH)₂ precipitate and Zn(OH)₄²⁻ ions. 5. Demonstrate the centrifugation step to remove Ni(OH)₂. 6. Show the addition of 6M HCl, neutralization of the solution, and its final pH adjustment to 7. 7. Show the addition of 1M Na₂CO₃ and the formation of ZnCO₃ precipitate. 8. Finish with the final separated ions—Ag⁺ as AgCl, Ni²⁺ as Ni(OH)₂, and Zn²⁺ as ZnCO₃.

Key concepts

Precipitation Reactions

Precipitation reactions are the cornerstones of many separation schemes in chemistry. They occur when two soluble ions react in solution to form an insoluble solid, known as a precipitate. This process is driven by the solubility rules, which predict which combinations of ions will form these insoluble compounds.

In our exercise, we start by adding 6M hydrochloric acid (HCl) to a solution of silver (Ag⁺), nickel (Ni²⁺), and zinc (Zn²⁺) ions. The Ag⁺ ion reacts with Cl- to form silver chloride (AgCl), a white precipitate. This is because AgCl is not soluble in water according to the solubility rules, allowing us to separate silver ions from the mixture. Unlike Ag⁺, Ni²⁺ and Zn²⁺ do not form precipitates with chloride ions and thus remain in solution at this stage.

The practical application of precipitation reactions is vast, spanning from analytical chemistry to wastewater treatment. Their predictability and the straightforward nature of the reactions make them a favorite in many industrial and laboratory processes.

Centrifugation Separation

Centrifugation is a technique used to separate particles based on their size, shape, and density. When the centrifuge spins, it generates a centrifugal force that pushes heavier components to the bottom of the tube, while lighter components stay in the supernatant, the liquid above the solid. It's particularly useful for separating precipitates from a solution because the solid particles typically have a higher density compared to the liquid.

In our problem, centrifugation is used twice. After adding HCl, we separate the AgCl precipitate. Further into the problem, when Ni(OH)₂ forms after the addition of NaOH, we use centrifugation again to separate the Ni(OH)₂ precipitate from the supernatant, which now contains Zn(OH)₄²⁻ ions. It's essential to ensure that all precipitates are adequately separated to avoid contamination in subsequent steps and achieve a high purity of isolated components. Efficient centrifugation is key for this, and parameters such as speed and time must be optimized for different precipitates.

Solution Neutralization

Solution neutralization is the process by which an acidic or basic solution is brought to a neutral pH of around 7. This is typically done by adding an acid to a basic solution or a base to an acidic solution. In the context of chemistry separations, neutralization can be critical for precipitating certain compounds at specific pH levels.

In the final phase of our separation scheme, we neutralize the solution with 6M HCl. After the previous step, our solution is basic due to the presence of NaOH, and we need to adjust the pH to create the right conditions for the precipitation of our final compound, ZnCO₃. By carefully controlling the amount of HCl added, we can precisely target a pH of 7, which is favorable for the addition of 1M sodium carbonate (Na₂CO₃) to precipitate ZnCO₃. The ability to control pH is a useful tool in the chemist's arsenal, allowing for the selective precipitation of compounds from complex mixtures based on their acid-base properties.