The Question is from neet-chemistry basic-chemistry-concepts , and it was created by the author Mr. S M HUSSAIN

Question

A colloidal solution of gold nanoparticles is prepared by reduction of $HAuCl_4$.  Which of the following methods is MOST EFFECTIVE for purifying this solution from excess reactants and small ionic byproducts?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Purification techniques for colloidal solutions
 **Related Topics**: Colloidal chemistry, dialysis, filtration, centrifugation, evaporation
 **Prerequisites**: Understanding of particle size in colloids and the principles behind different separation techniques.
## SOLUTION PATHWAY
**Given Information**:
A colloidal solution of gold nanoparticles is prepared, containing excess reactants and small ionic byproducts.
**Method & Steps**:
1. **Analyze the nature of the impurities:** Excess reactants and small ionic byproducts are much smaller than the gold nanoparticles.
2. **Evaluate separation techniques:**
    * **Filtration:**  Ineffective because the filter pores would be too large to retain the gold nanoparticles and the small ionic impurities would pass through.
    * **Centrifugation:** While centrifugation can separate particles based on size and density, it may not be effective in removing very small ionic impurities completely and could potentially aggregate the gold nanoparticles.
    * **Dialysis:** This technique uses a semi-permeable membrane that allows small ions and molecules (like excess reactants and byproducts) to pass through while retaining larger colloidal particles (gold nanoparticles). This is the most suitable method.
    * **Evaporation:** This would remove the solvent, but would leave behind both the gold nanoparticles and the impurities, not purifying the solution.
3. **Select the most effective method:** Dialysis is the most effective method for removing small ionic impurities while retaining the gold nanoparticles.
  Result: Dialysis
  Verification: Dialysis is a well-established technique for purifying colloids from small impurities.
 ## OPTION ANALYSIS
A :x: Filtration is ineffective for separating small particles from larger ones.
B :x: Centrifugation may not effectively remove small ionic impurities and could aggregate the nanoparticles.
C ✓: Dialysis selectively removes small ions and molecules while retaining the colloidal gold nanoparticles.
D :x: Evaporation removes the solvent but leaves behind both the nanoparticles and the impurities.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing dialysis with filtration: Dialysis uses a semi-permeable membrane, unlike simple filtration.
  2.Assuming centrifugation is always the best option for colloidal purification:  Centrifugation is more effective for larger particles.
 **Quick Tips**:
  1.Remember that dialysis is ideal for separating particles of significantly different sizes.
  2.Consider the size and nature of the impurities when choosing a purification method.

Mr. S M HUSSAIN · Answer

Filtration

Mr. S M HUSSAIN · Answer

Centrifugation

Mr. S M HUSSAIN · Answer

The correct Option is "Dialysis"

Mr. S M HUSSAIN · Answer

Evaporation

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