What Happens When Gelatin is Mixed with Gold Sol?

When gelatin is mixed with gold sol (a colloidal solution of gold particles suspended in water), an interesting interaction occurs. This is often studied in colloidal chemistry and is known as the "Gold Number" test. Here's what happens:

1. Gold Sol Stability

Gold sol consists of tiny gold nanoparticles dispersed in water. These particles are stabilized by an electrical charge on their surface. When gelatin is added to the gold sol, it can affect the stability of the colloidal gold.

2. Gelatin as a Stabilizing Agent

Gelatin contains proteins with charged groups that interact with the gold sol particles. The gelatin molecules may surround the gold particles, providing additional stabilization through physical adsorption, reducing the tendency of the gold particles to aggregate or coagulate. This stabilizing effect is why gelatin is used in the Gold Number test, which measures the ability of a substance (like gelatin) to stabilize the gold sol.

3. Change in Color

When gelatin is mixed with gold sol, the color of the solution may change depending on the concentration of gelatin and the size of the gold particles. This change is due to a phenomenon called scattering and plasmon resonance, where the gold particles interact with light. The addition of gelatin can modify this interaction, leading to visible color changes.

4. Aggregation of Gold Particles

At higher concentrations of gelatin, the gelatin molecules may aggregate the gold particles, leading to the formation of larger clusters. This results in a visible change in the appearance of the gold sol, such as a color change or the formation of precipitates.

Summary

When gelatin is mixed with gold sol, it can stabilize the colloidal suspension of gold particles. However, at higher concentrations of gelatin, the gold particles may aggregate, leading to changes in color and appearance. This interaction is important in the study of colloidal chemistry, particularly in the Gold Number test, which helps determine the amount of gelatin needed to stabilize the gold sol.