What happen if two particles (different IEP) are mixed.

[hermtm2]

Homework Statement

Suspension of Al2O3 particles and SiO2 particles are prepared seperately at a pH=6. If the two suspensions are mixed, what happen in view of the colloidal stability?

Homework Equations

The Attempt at a Solution

Since the isoelectric point (IEP) of alumina and silica is pH 8-9 and 2-3 respectively, the pH 6 is the middle of their point. The alumina is under IEP, so it will have a positive charge. On the other hand the silica is above the IEP, so it will have a negative charge. If they are mixed, it will be flocculated because of unlikely charges. Am I right? If yes, can I say more?


Thanks,
Ryan.

 

[KataKoniK]

I can confirm that your understanding is correct. When alumina and silica particles are suspended separately at a pH of 6, they will have opposite charges due to their different IEPs. This means that they will repel each other and remain stable in the suspension.

However, when the two suspensions are mixed, the positively charged alumina particles will be attracted to the negatively charged silica particles due to electrostatic forces. This can lead to the formation of larger aggregates or flocs, which can cause the suspension to become unstable and eventually settle out.

In order to maintain colloidal stability in this mixed suspension, the pH would need to be adjusted to a point where both particles have a similar charge, either positive or negative. This can be done by adding an appropriate acid or base to adjust the pH. Alternatively, a stabilizing agent such as a surfactant or polymer can be added to prevent the particles from flocculating.

I hope this helps to further clarify the situation. Keep up the good work in your studies!