How much water is to be added to 75 ml of alcohol so that the mixture contains 25% of alcohol?

To find the amount of water needed, we use the principle of dilution where the volume of the solute (alcohol) remains constant. The initial volume of pure alcohol is 75 ml. We want this 75 ml to represent 25% of the final mixture's total volume. Let the total volume of the final mixture be 'V'. According to the percentage formula, 25% of V = 75 ml, which simplifies to 0.25 * V = 75. Solving for V gives V = 75 / 0.25 = 300 ml. The total volume of the mixture is the sum of the alcohol and the added water. Therefore, the volume of water to be added is the total volume minus the initial alcohol volume: 300 ml - 75 ml = 225 ml [1]. This calculation ensures the alcohol concentration is reduced to the target 25% by increasing the solvent volume.

Sources

1. [1] https://www.mathcentre.ac.uk/resources/uploaded/diluting-a-solution.pdf