Which colloid can be coagulated by `Al^(+3)`?

Options

A. Haemoglobin
B. `TiO_(2)`
C. `As_(2)S_(3)`
D. CdS

Answer

To determine which colloid can be coagulated by Al^(3+), we need to analyze the nature of the colloids provided in the options and apply the principles of coagulation.

### Step-by-Step Solution:

1. **Understand Coagulation**: Coagulation is the process where colloidal particles aggregate and settle out of the solution. According to the Hardy-Schultz rule, the coagulating power of an ion is directly related to its valency. The higher the valency of the coagulating ion, the greater its ability to cause coagulation.

2. **Identify the Coagulating Ion**: In this case, the coagulating ion is Al^(3+), which has a valency of +3. This means it can effectively coagulate negatively charged colloids.

3. **Analyze the Given Colloids**:
- **Hemoglobin**: Hemoglobin is a protein and typically behaves as a positive colloid.
- **TiO2**: Titanium dioxide (TiO2) is also a positive colloid.
- **As2S3**: Arsenic trisulfide (As2S3) is a negative colloid due to the presence of sulfide ions (S^(2-)).
- **CdS**: Cadmium sulfide (CdS) is similarly a negative colloid because of the sulfide ions.

4. **Determine Which Colloids Can Be Coagulated**: Since Al^(3+) is a positively charged ion, it can coagulate negatively charged colloids. Therefore, As2S3 and CdS can be coagulated by Al^(3+).

5. **Conclusion**: The colloids that can be coagulated by Al^(3+) are As2S3 and CdS.

### Final Answer:
The colloids that can be coagulated by Al^(3+) are As2S3 and CdS.

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