100 ml of a colloidal solution is completely precipitated by addition of 0.5 ml 1M NaCl solution, calculate the coagulation value of NaCl.

Explanation

To calculate the coagulation value of NaCl, we can follow these steps:

### Step 1: Determine the millimoles of NaCl
The formula to calculate millimoles of a substance is given by:
\[ \text{Millimoles} = \text{Molarity} \times \text{Volume (in liters)} \times \text{n factor} \]

Given:
- Molarity of NaCl = 1 M
- Volume of NaCl solution = 0.5 ml = 0.5/1000 = 0.0005 L
- n factor for NaCl = 1 (since it dissociates into Na⁺ and Cl⁻)

Now, substituting the values:
\[ \text{Millimoles of NaCl} = 1 \, \text{mol/L} \times 0.0005 \, \text{L} \times 1 = 0.0005 \, \text{mol} = 0.5 \, \text{mmol} \]

### Step 2: Calculate the coagulation value
The coagulation value is calculated using the formula:
\[ \text{Coagulation value} = \frac{\text{Millimoles of NaCl}}{\text{Volume of colloidal solution (in liters)}} \]

Given:
- Volume of colloidal solution = 100 ml = 100/1000 = 0.1 L

Now substituting the values:
\[ \text{Coagulation value} = \frac{0.5 \, \text{mmol}}{0.1 \, \text{L}} = 5 \, \text{mmol/L} \]

### Final Answer
The coagulation value of NaCl is **5 mmol/L**.

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