Final answer:
When combining 20 mL of alcohol with 90 mL of distilled water, the resulting solution has a concentration of 18.18% v/v.
Step-by-step explanation:
To calculate the percentage volume/volume (% v/v) concentration of alcohol in a solution, you can use the formula:
volume of solute (alcohol) / total volume of solution × 100%
Given that the solution consists of 20 mL of alcohol and 90 mL of distilled water, the total volume of the solution is 20 mL + 90 mL = 110 mL. Using the above formula:
20 mL alcohol / 110 mL solution × 100% = 18.18%
Therefore, when 20 mL of alcohol is combined with 90 mL of distilled water, the resulting solution has an alcohol concentration of 18.18% v/v.