When a fresh precipitate is turned black in colloidal form, the process is called:

Options

A. Dialysis
B. Coagulation
C. Peptization
D. Electro-osmosis

Answer

To solve the question "When a fresh precipitate is turned black in colloidal form, the process is called:", we can follow these steps:

### Step 1: Understand the terms
- **Precipitate**: A solid that forms and settles out of a liquid mixture.
- **Colloidal form**: A mixture where very small particles are dispersed throughout a medium, which does not settle out.

### Step 2: Identify the process
- The question asks about the transformation of a fresh precipitate into a colloidal form.

### Step 3: Recall the relevant chemical processes
- The process of converting a precipitate into a colloidal form is known as **peptization**. This involves adding an electrolyte to the precipitate, which helps to break it down into smaller particles that can remain suspended in the liquid.

### Step 4: Explain the mechanism of peptization
- When an electrolyte (like FeCl3) is added to a freshly formed precipitate (like Fe(OH)3), the ions from the electrolyte adsorb onto the surface of the precipitate.
- This adsorption increases the repulsion between the particles, preventing them from aggregating and allowing them to remain in a colloidal state.

### Step 5: Conclusion
- Therefore, when a fresh precipitate is turned into a colloidal form, the process is called **peptization**.

### Final Answer:
The process is called **peptization**.

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