What is "gold number"?

6,221

A red gold sol is a colloidal suspension of gold nanoparticles with average size of particles less than 100 nm. The suspension is quite stable — the nanoparticles don't aggregate because of the existence of an electrical double layer on the surface of particles which causes electrostatic repulsion between the particles.

If you add a sufficient amount of an electrolyte (e.g., NaCl) to the colloid, the ions will disrupt the electric double layer which will cause aggregation (coagulation) of gold particles. A stabilizing agent (e.g., citric acid) is a compound that is able to adsorb on the surface of gold nanoparticles and protect them from aggregation (it acts like a shield), even in a high electrolyte concentration.

Share:
6,221
Aakash Kumar
Author by

Aakash Kumar

Love to learn !

Updated on January 28, 2020

Comments

  • Aakash Kumar
    Aakash Kumar almost 4 years

    I was reading about gold number and a book defined gold number as following:

    It is the minimum mass in milligrams of a stabilizing agent which is added to the 10 mL of red gold sol to protect it against coagulation caused by 1 mL of 10% (by mass) NaCl.

    Is this the definition? Because I am not able to understand above definition. Is NaCl used as the standard?

  • Archer
    Archer almost 5 years
    Why does colour change from red to violet?