How do you prepare 90 alcohol?

To prepare 90% alcohol, you can dilute a higher concentration of alcohol, such as 99% isopropyl alcohol or ethanol. Measure the desired volume of the 99% alcohol and then add distilled water in a calculated amount to achieve the 90% concentration. For example, to make 100 mL of 90% alcohol, mix 90 mL of 99% alcohol with 10 mL of distilled water. Always mix carefully and label the solution properly for safety.