What is meant by the colloidal state of matter? Explain the following terms:
(i) Multimolecular colloids (ii) electro-dialysis

Answer

### Step-by-Step Text Solution:

**1. Definition of Colloidal State of Matter:**
The colloidal state of matter is a type of mixture where insoluble particles of one substance are dispersed throughout another substance. The size of these dispersed particles typically ranges from 1 nanometer to 1000 nanometers (or 10^3 nanometers). This state is distinct from true solutions and suspensions, as the particles are larger than those found in true solutions but smaller than those in suspensions. Examples of colloidal systems include fog, milk, and smoke.

**2. Explanation of Multimolecular Colloids:**
Multimolecular colloids are formed when particles that are smaller than 1 nanometer come together to form aggregates or clusters. These aggregates have sizes that range from 1 nanometer to 1000 nanometers. The particles are held together by van der Waals forces. An example of multimolecular colloids is colloidal gold, where individual gold atoms cluster together to form larger particles that can be dispersed in a medium.

**3. Explanation of Electro-dialysis:**
Electro-dialysis is a separation process that involves the removal of ionic particles from a colloidal solution using an electric field. In this process, a container with a colloidal solution is set up with two electrodes: one positive and one negative. When an electric current is applied, the positively charged ions move towards the negative electrode, and the negatively charged ions move towards the positive electrode. This separation of charges allows for the effective removal of ionic particles from the colloidal state, making electro-dialysis a faster method compared to traditional dialysis.