Solution Preparation:

To prepare a solution containing 80% (v/v) ethanol, we need to determine the volume of ethanol required to be added to 250 ml of water.

Calculating the Volume of Ethanol:

To calculate the volume of ethanol, we can use the formula:

Volume of ethanol = (Percentage of ethanol / 100) x Total volume of solution

Here, the percentage of ethanol is 80% and the total volume of the solution is 250 ml.

Volume of ethanol = (80 / 100) x 250 ml
= 0.8 x 250 ml
= 200 ml

Therefore, 200 ml of ethanol should be added to 250 ml of water to obtain a solution containing 80% (v/v) ethanol.

Explanation:

When we say a solution is 80% (v/v) ethanol, it means that for every 100 ml of the solution, 80 ml of it is ethanol. Thus, to prepare the solution, we need to determine the volume of ethanol required.

The formula mentioned above is used to calculate the volume of a solute (ethanol in this case) when the percentage is given. By substituting the given values into the formula, we can find the volume of ethanol needed.

In this case, 200 ml of ethanol is needed because 80% of the total volume (250 ml) is ethanol. By adding 200 ml of ethanol to 250 ml of water, the resulting solution will contain 80% (v/v) ethanol.

Summary:

To prepare a solution containing 80% (v/v) ethanol, 200 ml of ethanol should be added to 250 ml of water. This can be calculated using the formula Volume of ethanol = (Percentage of ethanol / 100) x Total volume of solution. By substituting the given values, we find that 200 ml of ethanol is required.