Solution:


To make 0.02 M NaCl solution from 0.1 M NaCl solution, water needs to be added. The volume of water to be added can be calculated using the following formula:

M1V1 = M2V2

Where,
M1 = initial concentration of NaCl solution = 0.1 M
V1 = initial volume of NaCl solution = 500 ml
M2 = final concentration of NaCl solution = 0.02 M
V2 = final volume of NaCl solution

Step 1: Calculate the final volume of NaCl solution.

M1V1 = M2V2
0.1 x 500 = 0.02 x V2
V2 = (0.1 x 500) / 0.02
V2 = 2500 ml

Therefore, the final volume of NaCl solution is 2500 ml.

Step 2: Calculate the volume of water to be added.

The volume of water to be added is the difference between the final volume of NaCl solution and the initial volume of NaCl solution.

Volume of water = final volume – initial volume
Volume of water = 2500 ml – 500 ml
Volume of water = 2000 ml

Therefore, 2000 ml of water needs to be added to 500 ml of 0.1 M NaCl solution to make it 0.02 M NaCl solution.

Explanation:
When water is added to a solution, the concentration of the solution decreases. In this case, we need to decrease the concentration of 0.1 M NaCl solution to 0.02 M NaCl solution. So, we need to add water to the 0.1 M NaCl solution. The formula M1V1 = M2V2 is used to calculate the volume of water to be added. This formula is based on the principle of the conservation of mass. According to this principle, the mass of the solute before and after the dilution remains the same. Therefore, the product of the initial concentration and volume of the solute is equal to the product of the final concentration and volume of the solute. By using this formula, we can calculate the final volume of the solution and the volume of water to be added.